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[vsnet-grb-info 39467] GRB 250818B: GOTO optical counterpart candidate
by GCN Circulars 18 Aug '25

18 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41406 SUBJECT: GRB 250818B: GOTO optical counterpart candidate DATE: 25/08/18 05:44:49 GMT FROM: Amit Kumar at Royal Holloway - UoL/ U of Warwick, UK <amitkundu515(a)gmail.com> A. Kumar, S. Belkin, B. P. Gompertz, R. Starling, K. Ackley, M. J. Dyer, J. Lyman, K. Ulaczyk, D. O'Neill, B. Godson, D. Steeghs, D. K. Galloway, V. Dhillon, P. O'Brien, G. Ramsay, K. Noysena, R. Kotak, R. P. Breton, L. K. Nuttall, and J. Casares report on behalf of the GOTO collaboration: We report on observations with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022, Dyer et al. 2024) in response to SVOM/ECLAIRs GRB 250818B (sb25081801, Wang et al. GCN 41405). Targeted observations were performed at 2025-08-18 from 04:01:34 UT to 05:09:40 UT (from +0.54 to 1.67 h post-trigger, respectively). Each observation consisted of 4x90s exposures in the GOTO L-band (400-700 nm). Images were processed immediately after acquisition using the GOTO pipeline. Difference imaging was performed using deeper template observations. Source candidates were initially filtered using a classifier (Killestein et al. 2021) and cross-matched against a variety of contextual and minor planet catalogs. Human vetting was carried out in real time on any candidates that passed the above checks. We identify GOTO25fzq/AT 2025ukm as a new candidate optical counterpart within the SVOM/ECLAIRs 90% localisation region. We find no evidence of this source prior to the GRB trigger time in previous GOTO observations, the ZTF observations provided by the Lasair broker (Smith et al. 2019), or the ATLAS forced photometry server (Shingles et al. 2021). The GOTO observations, obtained 9.23 hours before the trigger, show no source at this position, with a 3-sigma limiting magnitude of L > 20.3 (AB). The source shows a clear decay and is a strong candidate optical counterpart to GRB 250818B. Name | RA(J2000) | Dec(J2000) | T-T0 (h) | Filter | Mag (AB) GOTO25fzq | 03:04:13.52 | -03:07:30.82 | 0.54 | L | 18.71 ± 0.14 | 1.67 | L | 19.49 ± 0.18 Magnitudes were calibrated using ATLAS-REFCAT2 (Tonry et al. 2018) and not corrected for Galactic extinction. GOTO (https://goto-observatory.org) is a network of telescopes that is principally funded by the STFC and operated at the Roque de los Muchachos Observatory on La Palma, Spain, and Siding Spring Observatory in NSW, Australia, on behalf of a consortium including the University of Warwick, Monash University, Armagh Observatory & Planetarium, the University of Leicester, the University of Sheffield, the National Astronomical Research Institute of Thailand (NARIT), the University of Turku, the University of Portsmouth, the University of Manchester and the Instituto de Astrofisica de Canarias (IAC). View this GCN Circular online at https://gcn.nasa.gov/circulars/41406. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39466] GRB 250818B: SVOM detection of a short burst
by GCN Circulars 18 Aug '25

18 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41405 SUBJECT: GRB 250818B: SVOM detection of a short burst DATE: 25/08/18 04:00:21 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Z. Q. Wang (GXU), Y. F. Liang (PMOC), W. J. Xie, D. H.Zhao (NAOC), F. Robinet (IJCLab), L. Zhang (IHEP), report on behalf of the SVOM mission team: At 2025-08-18T03:29:09 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 250818B (SVOM burst-id sb25081801). The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network. The burst was detected both by the Count-Rate Trigger (CRT) and the Image Trigger (IMT), which produced a sequence of 8 alerts. CRT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 10.74 in the [5-20] keV energy band over a time window of 2.50 seconds starting at 2025-08-18T03:29:08. The localization of the best alert is R.A., Dec. 46.0666, -3.1784 degrees: R.A. (J2000) = 3h04m15.99s Dec. (J2000) = -3d10m42.10s with a 90% confidence level (C.L.) radius of 7.44 arcmin (including systematic error of 2 arcmin added in quadrature). This burst also triggered SVOM/GRM at 2025-08-18T03:29:08 on a timescale of 1 seconds with an SNR of 6.80. https://www.bursthub.cn//admin/static/svgrb250818B.png SVOM slewed to the burst. However, the MXT was occulted by the Earth. The burst localization results will be published later in another GCN circular. A SVOM ToO has been programmed for follow-up. The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. SVOM/ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC. SVOM/GRM was developed by the Institute of High Energy Physics (IHEP) of CAS. SVOM/MXT was developed jointly by CNES, CEA-IRFU, CNRS-IJCLab, University of Leicester, MPE. The Burst Advocate (BA) on shift for this alert is Ziqi.Wang: ziqi.wang(a)st.gxu.edu.cn. Please contact the BA by email if you require additional information. View this GCN Circular online at https://gcn.nasa.gov/circulars/41405. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39465] LIGO/Virgo/KAGRA S250818t: Identification of a GW compact binary merger candidate
by GCN Circulars 18 Aug '25

18 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41404 SUBJECT: LIGO/Virgo/KAGRA S250818t: Identification of a GW compact binary merger candidate DATE: 25/08/18 02:52:38 GMT FROM: Jiyoon Sun <jiyoon.sun.h(a)gmail.com> The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report: We identified the compact binary merger candidate S250818t during real-time processing of data from LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) at 2025-08-18 02:08:58.392 UTC (GPS time: 1439518156.392). The candidate was found by the GstLAL [1], MBTA [2], and PyCBC Live [3] analysis pipelines. S250818t is an event of interest because its false alarm rate, as estimated by the online analysis, is 1.7e-11 Hz, or about one in 1e3 years. The event's properties can be found at this URL: https://gracedb.ligo.org/superevents/S250818t The classification of the GW signal, in order of descending probability, is BBH (>99%), Terrestrial (<1%), BNS (<1%), or NSBH (<1%). Assuming the candidate is astrophysical in origin, the probability that at least one of the compact objects is consistent with a neutron star mass (HasNS) is <1%. [4] Using the masses and spins inferred from the signal, the probability of matter outside the final compact object (HasRemnant) is <1%. [4] Both HasNS and HasRemnant consider the support of several neutron star equations of state for maximum neutron star mass. The probability that either of the binary components lies between 3 and 5 solar masses (HasMassGap) is 2%. The source chirp mass falls with highest probability in the bin (5.5, 11.0) solar masses, assuming the candidate is astrophysical in origin. Two sky maps are available at this time and can be retrieved from the GraceDB event page: * bayestar.multiorder.fits,0, an initial localization generated by BAYESTAR [5], distributed via GCN and SCiMMA notices about 32 seconds after the candidate event time. * bayestar.multiorder.fits,1, an initial localization generated by BAYESTAR [5], distributed via GCN and SCiMMA notices about 5 minutes after the candidate event time. The preferred sky map at this time is bayestar.multiorder.fits,1. For the bayestar.multiorder.fits,1 sky map, the 90% credible region is 377 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 1311 +/- 350 Mpc (a posteriori mean +/- standard deviation). For further information about analysis methodology and the contents of this alert, refer to the LIGO/Virgo/KAGRA Public Alerts User Guide https://emfollow.docs.ligo.org/. [1] Tsukada et al. PRD 108, 043004 (2023) doi:10.1103/PhysRevD.108.043004 and Ewing et al. PRD 109, 042008 (2024) doi:10.1103/PhysRevD.109.042008 [2] Alléné et al. CQG 42, 105009 (2025) doi:10.1088/1361-6382/add234 [3] Dal Canton et al. ApJ 923, 254 (2021) doi:10.3847/1538-4357/ac2f9a [4] Chatterjee et al. ApJ 896, 54 (2020) doi:10.3847/1538-4357/ab8dbe [5] Singer & Price PRD 93, 024013 (2016) doi:10.1103/PhysRevD.93.024013 View this GCN Circular online at https://gcn.nasa.gov/circulars/41404. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39464] GRB 250818A: Swift detection of a burst
by GCN Circulars 18 Aug '25

18 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41403 SUBJECT: GRB 250818A: Swift detection of a burst DATE: 25/08/18 01:48:57 GMT FROM: K.L. Page at U Leicester <klp5(a)leicester.ac.uk> S. B. Cenko (GSFC), C. Gronwall (PSU), R. Gupta (NASA GSFC), H. A. Krimm (NSF), A. Y. Lien (U Tampa), K. L. Page (U Leicester), D. M. Palmer (LANL) and M. H. Siegel (PSU) report on behalf of the Neil Gehrels Swift Observatory Team: At 01:31:22 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 250818A (trigger=1343270). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 213.833, -58.007 which is RA(J2000) = 14h 15m 20s Dec(J2000) = -58d 00' 26" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). Due to a communications gap, only the BAT light curve after T+8s is available. This later lightcurve shows a complex structure out to at least T+150s. The peak count rate in the available lightcurve was ~5500 counts/sec (15-350 keV), at ~80 sec after the trigger. The XRT began observing the field at 01:33:00.6 UT, 97.9 seconds after the BAT trigger. XRT found a bright, uncatalogued X-ray source located at RA, Dec 213.8002, -58.0134 which is equivalent to: RA(J2000) = 14h 15m 12.05s Dec(J2000) = -58d 00' 48.2" with an uncertainty of 4.9 arcseconds (radius, 90% containment). This location is 66 arcseconds from the BAT onboard position, within the BAT error circle. Despite the onboard localisation, no X-ray source was detected in 45 s of promptly-downlinked data, suggesting that the initial centroid may equally have been a cosmic ray. This position should therefore be treated with caution. The initial flux in the 0.1 s image was 1.09e-07 erg cm^-2 s^-1 (0.2-10 keV). UVOT took a finding chart exposure of 250 seconds with the U filter starting 162 seconds after the BAT trigger. No credible afterglow candidate has been found in the initial data products. The 2.7'x2.7' sub-image covers none of the XRT error circle. The 8'x8' region for the list of sources generated on-board covers 100% of the XRT error circle. Because of the density of catalogued stars, further analysis is required to report an upper limit for any afterglow in the region. No correction has been made for the large, but uncertain, extinction expected. Burst Advocate for this burst is S. B. Cenko (brad.cenko AT nasa.gov) Please contact the BA by email if you require additional information regarding Swift followup of this burst. In extremely urgent cases, after trying the Burst Advocate, you can contact the Swift PI by phone (see Swift TOO web site for information: http://www.swift.psu.edu/) View this GCN Circular online at https://gcn.nasa.gov/circulars/41403. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39463] GRB 250818A: Fermi GBM Final Real-time Localization
by GCN Circulars 18 Aug '25

18 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41402 SUBJECT: GRB 250818A: Fermi GBM Final Real-time Localization DATE: 25/08/18 01:42:02 GMT FROM: Fermi GBM Team at MSFC/Fermi-GBM <do_not_reply(a)GIOC.nsstc.nasa.gov> The Fermi GBM team reports the detection of a likely LONG GRB At 01:31:22 UT on 18 Aug 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250818A (trigger 777173487.99771 / 250818063). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 232.7, Dec = -62.9 (J2000 degrees, equivalent to J2000 15h 30m, -62d 53'), with a statistical uncertainty of 7.8 degrees. The angle from the Fermi LAT boresight is 140.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250818063/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250818063/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250818063/… View this GCN Circular online at https://gcn.nasa.gov/circulars/41402. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39462] sb25081602: Swift-XRT observations
by GCN Circulars 17 Aug '25

17 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41401 SUBJECT: sb25081602: Swift-XRT observations DATE: 25/08/17 11:56:08 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> P.A. Evans (U. Leicester), J.A. Kennea (PSU), E. Ambrosi (INAF-IASFPA) , A.P. Beardmore (U. Leicester), M.G. Bernardini (INAF-OAB), R. Brivio (INAF-OAB), D.N. Burrows (PSU), S. Campana (INAF-OAB), M. Capalbi (INAF-OAR), A. D'Ai (INAF-IASFPA), P. D'Avanzo (INAF-OAB), V. D'Elia (SSDC & INAF-OAR), S. Dichiara (PSU), M. Ferro (INAF-OAB), A. Melandri (INAF-OAR), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), M. Perri (SSDC & INAF-OAR), C. Salvaggio (INAF-OAB), T. Sbarrato (INAF-OAB), B. Sbarufatti (INAF-OAB), M.A. Williams (PSU) report on behalf of the Swift-XRT team: Swift-XRT has performed follow-up observations of the SVOM/ECLAIRs-detected source sb25081602, collecting 1.7 ks of Photon Counting (PC) mode data between T0+1.8 ks and T0+7.3 ks after the trigger. We have detected 2 sources. These have been automatically classified as follows: * 0 likely counterparts * 0 candidate counterparts * 0 uncatalogued X-ray sources * 2 known X-ray sources Known X-ray sources ------------------- Source 1 (SWIFT J051406.2-400234): ================================== RA (J2000.0): 78.5261 = 05h 14m 06.26s Dec (J2000.0): -40.0430 = -40d 02' 34.8" Error: 3.5 (arcsec, radius, 90% confidence). Detect flag: GOOD Distance: 3.7 arcmin from the SVOM/ECLAIRs position. Mean rate: 3.58 +/- 0.14 ct s^-1 Mean flux: (1.474 +/- 0.058)e-10 erg cm^-2 s^-1 Peak rate: 6.7 +/- 1.5 ct s^-1 Peak flux: (2.75 +/- 0.62)e-10 erg cm^-2 s^-1 ECF: 4.11e-11 erg cm^-2 ct^-1 assuming NH=9.61e+20 cm^-2, gamma=1.65 determined from a spectral fit. This matches a catalogued X-ray source LSXPS J051406.5-400237 in the LSXPS catalogue. Details: Separation: 4.4" from the XRT source Cat Rate: 5.0e+00 +/- 2.1e-02 ct s^-1 Cat Flux: 2.1e-10 +/- 8.6e-13 erg cm^-2 s^-1 (0.3-10 keV) so the source is 1.1-sigma above the catalogued flux. There is no evidence for fading. This is 3.05" from the SIMBAD position of 4U 0513-40, noted by Magnani et al. (GCN Circ. 41399). There are 10 2MASS objects within the source's 3-sigma error radius. Source 2 (SWIFT J051413.9-395933): ================================== RA (J2000.0): 78.5583 = 05h 14m 13.99s Dec (J2000.0): -39.9927 = -39d 59' 33.7" Error: 5.8 (arcsec, radius, 90% confidence). Detect flag: REASONABLE Distance: 2.1 arcmin from the SVOM/ECLAIRs position. Mean rate: (-1.0 +/- -1.0)e0 ct s^-1 Mean flux: (-2.2 +/- -2.2)e-11 erg cm^-2 s^-1 Peak rate: (4.5 [+2.6, -2.1])e-3 ct s^-1 Peak flux: (9.6 [+5.6, -4.4])e-14 erg cm^-2 s^-1 ECF: 2.16e-11 erg cm^-2 ct^-1 assuming NH=1.21e+22 cm^-2, gamma=9.85 determined from a spectral fit. This matches a catalogued X-ray source LSXPS J051414.3-395936 in the LSXPS catalogue. Details: Separation: 4.6" from the XRT source Cat Rate: 0.0e+00 +/- 2.3e-04 ct s^-1 Cat Flux: 0.0e+00 +/- 5.1e-15 erg cm^-2 s^-1 (0.3-10 keV) so the source is 1.9-sigma above the catalogued flux. There is no evidence for fading. All fluxes are 0.3-10 keV, observed. For all flux conversions and comparisons with catalogues and upper limits from other missions, we assumed a power-law spectrum with NH=3x10^20 cm^-2 and photon index (Gamma)=1.7 unless otherwise stated. The results of the XRT-team automatic analysis of the XRT observations, including a position-specific upper limit calculator, are available at https://www.swift.ac.uk/SVOM/SVOM_FIELD00030. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/41401. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39461] GRB 250816A: SVOM/GRM observation of a short burst
by GCN Circulars 17 Aug '25

17 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41400 SUBJECT: GRB 250816A: SVOM/GRM observation of a short burst DATE: 25/08/17 07:41:19 GMT FROM: Chenwei Wang at IHEP <cwwang(a)ihep.ac.cn> SVOM/GRM team: Chen-Wei Wang, Zheng-Hang Yu, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Olivier GODET (IRAP) Report on behalf of the SVOM team: SVOM/GRM was triggered in-flight by a short burst GRB 250816A (SVOM trigger reference: sb25081601) at 2025-08-16T01:30:10.600 UTC (T0), which is also detected by Fermi/GBM (Fermi GBM Team, GCN #41397). With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of a single pulse with a T90 of 0.9 +0.5/-0.4 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb250816A.png In addition, the position of this burst, as determined by Fermi/GBM (RA= 156.7, DEC= 58.9, GCN #41397), is located at about 115 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view. ECLAIRs was not collecting data at the time of this burst. With this localization, the time-averaged spectrum from T0-0.3 to T0+0.2 s is best fitted by a power law function. The power law index is -2.17 +/-0.15. The event fluence (10-1000 keV) in this time interval is (1.97 +/-0.24)E-06 erg/cm^2. The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. GRM is developed by the Institute of High Energy Physics (IHEP) of CAS. The SVOM point of contact for this burst is: Chen-Wei Wang (IHEP)(cwwang(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/41400. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39460] SVOM/sb25081602: detection of a likely X-ray transient
by GCN Circulars 16 Aug '25

16 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41399 SUBJECT: SVOM/sb25081602: detection of a likely X-ray transient DATE: 25/08/16 16:22:46 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> F. Magnani (CPPM), D. Dornic (CPPM), O. Godet (IRAP), H. Goto (Kanazawa Univ.) report on behalf of the SVOM mission team: At 2025-08-16T15:31:20 UTC (T0), SVOM/ECLAIRs triggered and located a likely X-ray transient (SVOM burst-id sb25081602). The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network. The burst was only detected by the Count-Rate Trigger (CRT), which produced a sequence of 3 alerts. CRT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 9.53 in the [5-20] keV energy band over a time window of 20.40 seconds starting at 2025-08-16T15:31:10. The localization of the best alert is R.A., Dec. 78.514, -39.982 degrees: R.A. (J2000) = 5h14m03.43s Dec. (J2000) = -39d58m56.04s with a 90% confidence level (C.L.) radius of 8.33 arcmin (including systematic error of 2 arcmin added in quadrature). The LMXB 4U 0513-40 is located at 3.75 arcmin from the ECLAIRs position. We note that there are other X-ray sources within the ECLAIRs error circle. SVOM did not slew. No X-ray observation could be performed by SVOM/MXT for the time being. No optical observation could be performed by SVOM/VT for the time being. The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. SVOM/ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC. SVOM/GRM was developed by the Institute of High Energy Physics (IHEP) of CAS. SVOM/MXT was developed jointly by CNES, CEA-IRFU, CNRS-IJCLab, University of Leicester, MPE. The Burst Advocate (BA) on shift for this alert is F. Magnani (francesco.magnani.work(a)gmail.com) Please contact the BA by email if you require additional information. View this GCN Circular online at https://gcn.nasa.gov/circulars/41399. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39459] Fermi GRB 250814B: Global MASTER-Net observations report
by GCN Circulars 16 Aug '25

16 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41398 SUBJECT: Fermi GRB 250814B: Global MASTER-Net observations report DATE: 25/08/16 03:56:27 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A.Sosnovskij (CrAO), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-Kislovodsk robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) started inspect of the Fermi GRB 250814B ( Fermi GBM team, GCN 41366) errorbox 47497 sec after notice time and 47527 sec after trigger time at 2025-08-14 23:34:17 UT, with upper limit up to 16.5 mag. The observations began at zenith distance = 119 deg. The sun altitude is -74.1 deg. The galactic latitude b = -6 deg., longitude l = 181 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2968279 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 47557 | 2025-08-14 23:34:17 | MASTER- | (05h 18m 51.95s , +23d 45m 27.2s) | C | 60 | 14.0 | 47557 | 2025-08-14 23:34:17 | MASTER-Kislovodsk | (05h 14m 32.17s , +24d 08m 32.4s) | C | 60 | 16.5 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. View this GCN Circular online at https://gcn.nasa.gov/circulars/41398. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39458] GRB 250816A: Fermi GBM Final Real-time Localization
by GCN Circulars 16 Aug '25

16 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41397 SUBJECT: GRB 250816A: Fermi GBM Final Real-time Localization DATE: 25/08/16 01:40:45 GMT FROM: Fermi GBM Team at MSFC/Fermi-GBM <do_not_reply(a)GIOC.nsstc.nasa.gov> The Fermi GBM team reports the detection of a likely SHORT GRB At 01:30:10 UT on 16 Aug 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250816A (trigger 777000615.453666 / 250816063). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 156.7, Dec = 58.9 (J2000 degrees, equivalent to J2000 10h 26m, 58d 53'), with a statistical uncertainty of 3.0 degrees. The angle from the Fermi LAT boresight is 40.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250816063/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250816063/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250816063/… View this GCN Circular online at https://gcn.nasa.gov/circulars/41397. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39457] GRB 250814A: Swift-BAT refined analysis
by GCN Circulars 15 Aug '25

15 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41396 SUBJECT: GRB 250814A: Swift-BAT refined analysis DATE: 25/08/15 21:11:04 GMT FROM: Amy <yarleen(a)gmail.com> H. A. Krimm (NSF), S. D. Barthelmy (GSFC), R. Caputo (GSFC), R. Gupta (GSFC), S. Laha (GSFC/UMBC), A. Y. Lien (U Tampa), C. B. Markwardt (GSFC), M. J. Moss (GSFC), D. M. Palmer (LANL), T. Parsotan (GSFC), D. Sadaula (GSFC/UMBC), T. Sakamoto (AGU) (i.e. the Swift-BAT team): Using the data set from T-239 to T+963 sec from the recent telemetry downlink, we report further analysis of BAT GRB 250814A (trigger #1342439) (Caputo et al., GCN Circ. 41358). The BAT ground-calculated position is RA, Dec = 306.313, 48.406 deg which is RA(J2000) = 20h 25m 15.2s Dec(J2000) = +48d 24' 23.1" with an uncertainty of 1.9 arcmin, (radius, sys+stat, 90% containment). The partial coding was 54%. The mask-weighted light curve shows a single-pulse structure that starts at ~T0 and peaks at ~T+10 s. The main pulse ends at ~T+25 s, but there is some weak emission that lasts till ~T+100 s. T90 (15-350 keV) is 110.11 +- 47.90 sec (estimated error including systematics). The time-averaged spectrum from T+1.06 to T+125.36 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.91 +- 0.21. The fluence in the 15-150 keV band is 1.4 +- 0.2 x 10^-06 erg/cm2. The 1-sec peak photon flux measured from T+10.22 sec in the 15-150 keV band is 0.8 +- 0.2 ph/cm2/sec. All the quoted errors are at the 90% confidence level. The results of the batgrbproduct analysis are available at https://swift.gsfc.nasa.gov/results/batgrbcat/BAT_refined_circular/1342439 View this GCN Circular online at https://gcn.nasa.gov/circulars/41396. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39456] GRB 250815A: Fermi GBM Final Localization
by GCN Circulars 15 Aug '25

15 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41395 SUBJECT: GRB 250815A: Fermi GBM Final Localization DATE: 25/08/15 15:51:47 GMT FROM: Utkarsh Pathak at IIT Bombay <utkarshpathak.07(a)gmail.com> The Fermi GBM team reports the detection of a likely SHORT GRB "At 11:49:10.84 UT on 15 August 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250815A (trigger 776951355/250815492). The duration and the spectrum suggest an SGR flare, but it is not near the galactic plane, so further follow-up is encouraged. The on-ground calculated location, using the Fermi GBM trigger data, is RA = 221.57, Dec = -1.10 (J2000 degrees, equivalent to J2000 14h 46m, -1d 6'), with a statistical uncertainty of 7.79 degrees. The angle from the Fermi LAT boresight is 30 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250815492/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250815492/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250815492/…" View this GCN Circular online at https://gcn.nasa.gov/circulars/41395. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39455] GRB 250813B: Liverpool Telescope optical upper limits
by GCN Circulars 15 Aug '25

15 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41394 SUBJECT: GRB 250813B: Liverpool Telescope optical upper limits DATE: 25/08/15 14:54:03 GMT FROM: Amit Kumar at Royal Holloway - UoL/ U of Warwick, UK <amitkundu515(a)gmail.com> A. Kumar, J. R. Maund (RHUL), N. C. Sun (UCAS), W. X. Li, Y. N. Wang (NAOC), and K. Wiersema (Herts) report: Using the IO:O imager on the 2.0 m Liverpool Telescope, we observed the field of the SVOM/ECLAIRs–triggered GRB 250813B (Xie et al., GCNs 41352, 41354), also detected by EP–FXT (Wu et al., GCN 41361), SVOM/MXT (Götz et al., GCN 41368), Fermi/GBM (Smith et al., GCN 41376), and SVOM/GRM (Tan et al., GCN 41383). Observations in the r and z bands were obtained on 2025-08-15 at 02:42:32.1 UT and 03:13:37.8 UT, corresponding to ~1.16 and ~1.18 days post-trigger, respectively. Each band consisted of 3 × 600 s exposures. We do not detect the optical afterglow of GRB 250813B (Jelinek et al., GCN 41355; de Ugarte Postigo et al., GCN 41356; Schneider et al., GCN 41363; Xin et al., GCN 41369; Corcoran et al., GCN 41370) down to limiting magnitudes of r >22.0 and z >20.6. Photometric calibration was performed using Pan-STARRS stars. The quoted magnitudes are not corrected for Galactic extinction in the direction of the GRB. View this GCN Circular online at https://gcn.nasa.gov/circulars/41394. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39454] GRB 250814A: Further COLIBRÍ optical upper limit
by GCN Circulars 15 Aug '25

15 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41393 SUBJECT: GRB 250814A: Further COLIBRÍ optical upper limit DATE: 25/08/15 14:48:30 GMT FROM: Alan Watson at UNAM <alan(a)astro.unam.mx> Enrique Moreno Méndez (UNAM), Francesco Magnani (CPPM), Jean-Grégoire Ducoin (CPPM), Alan M. Watson (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Fredd Sánchez Álvarez (UNAM), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (OCA), Jean-Luc Atteia (IRAP), Rosa L. Becerra (U Roma), Nathaniel R. Butler (ASU) , Damien Dornic (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Benjamin Schneider (LAM), and Antonio de Ugarte Postigo (LAM) report: We imaged the field of the Fermi and Swift GRB 250814A (Fermi team, GCN Circ. 41357, Caputo et al. GCN Circ. 41358) using the DDRAGO wide-field imager on the COLIBRÍ telescope. We observed from 2025-08-15 03:20 to 04:48 UTC (from 19.8 to 21.2 hours after the trigger) and obtained 64 minutes of exposure in the r filter. The data were reduced and coadded with the COLIBRÍ pipeline and analysed with STDWeb/STDPipe (Karpov 2025). The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction. In the stacked image, we do not detect any new source at the XRT source position (Caputo et al. GCN Circ. 41358) or possible optical and infrared counterpart position (Karambelkar et al. GCN Circ. 41377; Castro-Tirado et al., GCN Circ. 41381; Ahumada et al. GCN Circ. 41382; D'Avanzo et al. GCB Circ. 41391; Kumar et al. GCN Circ. 41392) down to the following 3-sigma limit: r > 23.6 We thank the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir and the COLIBRÍ and DDRAGO engineering teams. COLIBRÍ is an astronomical observatory developed and operated jointly by France (AMU, CNES and CNRS) and Mexico (UNAM and SECIHTI). It is located at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, Mexico. View this GCN Circular online at https://gcn.nasa.gov/circulars/41393. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39453] GRB 250814A: detection of the afterglow candidate with Liverpool Telescope
by GCN Circulars 15 Aug '25

15 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41392 SUBJECT: GRB 250814A: detection of the afterglow candidate with Liverpool Telescope DATE: 25/08/15 13:59:44 GMT FROM: Amit Kumar at Royal Holloway - UoL/ U of Warwick, UK <amitkundu515(a)gmail.com> A. Kumar, J. R. Maund (RHUL), N. C. Sun (UCAS), W. X. Li, Y. N. Wang (NAOC), and K. Wiersema (Herts) report: We observed the field of the Fermi/GBM and Swift/BAT GRB 250814A (Fermi GBM Team, GCN 41357; Caputo et al., GCN 41358), which is spatially coincident with the sub-threshold GW trigger S250814bg (LVK, GCN 41364), using the IO:O imager on the 2.0m Liverpool Telescope. Multi-band (B, g, V, r, i, and z bands) imaging was obtained between 2025-08-14 23:34:48.3 UT and 2025-08-15 01:29:02.2 UT (corresponding to ~15.99 and 17.90 hours post-trigger, respectively). Based on our preliminary analysis, we detect the counterpart candidate in our stacked z-band image obtained ~16.86 hours post-trigger at RA = 20:25:13.8 and Dec = +48:23:56.5 (J2000), within the Swift-XRT localisation region (Salvaggio et al., GCN 41379); see also Karambelkar et al. (GCN 41377), Castro-Tirado et al. (GCN 41381), Ahumada et al. (GCN 41382) and Source 1 of D'Avanzo et al. (GCN 41391). No source is detected at this position in the B, g, V, r, and i bands. A summary of our observations and preliminary photometric results is provided below. T_obs (start time) T_obs - T0 Exp Filter Mag -------------------------------------------------------------------------------------------- 2025-08-15T00:26:48.9 16.86 2x600 s z 21.3 ± 0.3 2025-08-14T23:34:48.3 15.99 600 s g >21.9 2025-08-14T23:45:18.2 16.16 2x600 s r >22.1 2025-08-15T00:06:03.3 16.51 2x600 s i >21.8 2025-08-15T00:47:35.3 17.21 2x600 s V >22.2 2025-08-15T01:08:24.4 17.55 3x600 s B >20.5 Photometric calibration was performed using stars from the Pan-STARRS (for g, r, i and z bands), USNO-B1 (for B band), and APASS (for V band) catalogues. The quoted magnitudes are not corrected for Galactic extinction in the direction of the GRB. This circular may be cited. View this GCN Circular online at https://gcn.nasa.gov/circulars/41392. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39452] GRB 250814A: GRAWITA TNG NIR observations
by GCN Circulars 15 Aug '25

15 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41391 SUBJECT: GRB 250814A: GRAWITA TNG NIR observations DATE: 25/08/15 12:07:02 GMT FROM: Paolo D'Avanzo at INAF - OAB <paolo.davanzo(a)inaf.it> P. D'Avanzo, (INAF-OAB), M.T. Botticella, L. Izzo (INAF - OACn), A. Rossi (INAF-OAS), V. D’Elia (ASI-SSDC), G. Greco (INFN), M.G. Bernardini (INAF-OAB), B. Patricelli (Univ. Pisa), E. Cappellaro (INAF-OAPd), E. Brocato (INAF-OAR), V. Lorenzi, G Mainella (INAF-TNG), on behalf of GRAWITA report: We observed the field of GRB 250814A detected by Swift/BAT and Fermi/GBM (Caputo et al. GCN Circ. 41358; Fermi team, GCN Circ. 41357) and possibly associated with the sub-threshold GW trigger S250814bg (LVK, GCN Circ. 41364) with the Italian 3.6m TNG telescope, located in Canary Islands (Spain), equipped with the near-infrared camera NICS in imaging mode. A series of images were obtained with the H filter starting on 2025-08-14T20:33:39 UT (i.e. 13.0 hours post T0) and with the K filter starting on 2025-08-14T22:06:25 UT (i.e. 14.5 hours post T0), centered at the position of the X-ray afterglow detected by Swift/XRT (Caputo et al. GCN Circ. 41358; Salvaggio et al., GCN Circ. 41379). Within the Swift/XRT error circle (Salvaggio et al., GCN Circ. 41379) we detect two sources. Below we report the source positions and AB magnitudes derived from preliminary photometry (calibrated against the 2MASS catalogue). Source 1 RA (J2000) = 20:25:13.86 Dec (J2000) = +48:23:56.3 +/- 0.3" H = 21.3 +/- 0.2 mag K = 21.4 +/- 0.3 mag Source 2 RA (J2000) = 20:25:14.06 Dec (J2000) = +48:23:54.8 +/- 0.3" H = 21.8 +/- 0.2 mag K = 21.2 +/- 0.2 mag We note that Source 1 is the same reported by several authors in both the NIR and optical bands (Karambelkar et al. GCN Circ. 41337; Castro-Tirado et al. GCN Circ. 41381; Ahumada et al. GCN Circ. 41382). Compared with the results reported so far, our preliminary photometry suggests that this source has not varied, in agreement with the findings of Ahumada et al. (GCN Circ. 41382). Further NIR observations are encouraged to check for any brightness evolution of Source 2. View this GCN Circular online at https://gcn.nasa.gov/circulars/41391. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39451] GRB 250812A: SVOM/VT optical continued observation
by GCN Circulars 15 Aug '25

15 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41390 SUBJECT: GRB 250812A: SVOM/VT optical continued observation DATE: 25/08/15 10:57:59 GMT FROM: Yinuo Ma <mayn(a)bao.ac.cn> Y. N. Ma, Z. H. Yao, L. P. Xin, Y. L. Qiu, C. Wu, H. L. Li, X. H. Han, Y. Xu, J. Wang, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA), Z. M. Wang (BNU) report on behalf of the SVOM/VT team. SVOM/VT conducted continued observations of GRB 250812A detected by SVOM/ECLAIRs（Xin et al., GCN 41322). The magnitudes of the optical afterglow (He et al., GCN 41324; Xin et al., GCN 41326; Rakotondrainibe et al., GCN 41328; Freeberg et al., GCN 41331; Siegel et al., GCN 41344; Santos et al., GCN 41346; van Dalen et al., GCN 41347; de Ugarte Postigo et al., GCN 41348) are: mid time (h) | exposure time (s) | band | mag (AB) | mag err -------------|-------------------|-- ---|----------|-------- 66.572 | 20*70 | VT_R | 21.25 | 0.07 66.572 | 20*70 | VT_B | 21.81 | 0.09 Our photometry was not corrected for Galactic extinction. The optical afterglow initially rises with a temporal slope of 0.5, reaching its peak at approximately 18 hours, followed by a rapid decay with a slope of -2.0. The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Centre for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS. View this GCN Circular online at https://gcn.nasa.gov/circulars/41390. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39450] GRB 250814A: Mondy optical observations of the candidate counterpart to LVK S250814bg
by GCN Circulars 15 Aug '25

15 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41389 SUBJECT: GRB 250814A: Mondy optical observations of the candidate counterpart to LVK S250814bg DATE: 25/08/15 10:55:07 GMT FROM: Nicolai Pankov at HSE, IKI RAS <colinsergesen(a)gmail.com> N. Pankov (HSE, IKI), A. Pozanenko (IKI), E. Klunko (ISTP) report on behalf of IKI-GRB-FuN: We observed the field of GRB 250814A detected by Fermi/GBM (The Fermi GBM team, GCN 41357), Swift/BAT (Caputo et. al, GCN 41358), which was temporally and spatially coincident with a GW event S250814bg detected by LVK (GCN 41364). The observations were carried out with the 1.5m AZT-33IK telescope of the Solar Sayan Observatory (Mondy). The series of 30x120 s images were captured in the R-filter starting on 2025-08-14 at 17:49 UT, i.e. ~0.44 days after the GBM trigger. In the co-add image of 28x120 s we do not detect any optical source at the position of the IR candidate (Karambelkar et. al, GCN 41377; Castro-Tirado et. al, GCN 41381; Ahumada et. al, GCN 41382). The preliminary upper limit on a candidate optical counterpart in the co-add image is presented below: Date UT start t-T0 Exp. Filter OT Err UL (mid, days) (n x s) (3sigma) 2025-08-14 17:51:08 0.44721 28x120 R n/d n/d 22.7 The photometry was calibrated using nearby stars from the PS1 DR2 catalog (R mags were obtained via Lupton 2005 transformations) and not corrected for the Galactic extinction. The candidate counterpart position was also observed in the optical and IR bands by (Becerra et. al, GCN 41362; de Ugarte Postigo et. al, GCN 41367; Karambelkar et.al, GCN 41372; Salazar Manzano et. al, GCN 41375; Jiang et. al, GCN 41387), which resulted in upper limits. View this GCN Circular online at https://gcn.nasa.gov/circulars/41389. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39449] GRB 250813B: Calapai Observatory, Massa S. Giorgio (Messina), upper limit
by GCN Circulars 15 Aug '25

15 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41388 SUBJECT: GRB 250813B: Calapai Observatory, Massa S. Giorgio (Messina), upper limit DATE: 25/08/15 10:13:58 GMT FROM: Giovanni Calapai at Calapai Astronomical Observatory, Massa S. Giorgio, Messina, Italy <giovannicalapai(a)tiscali.it> Giovanni Calapai at Calapai Astronomical Observatory, Massa S. Giorgio, (Messina) Italy Member of: GRB/UAI Gamma Ray Burst Section of Unione Astrofili Italiani. Report: We imaged the field of GRB 250813B detected by SVOM/ECLAIRs telescope (Xie et al. GCN 41352 - 41354), with the 11 inches Schmidt-Cassegrain (Celestron 11) telescope F/D=6,3. The observations were started at 2025-08-14 00:02 UT (approximately 1.19 hours after burst) stacking a set of unfiltered CCD image. The observations were carried out with partially clear skies and Moon (illumination: 74%, distance: 42°). We co-added 93 exposures of 60 sec each. Start T0+ End T0+ CR lim 1.19 hour 4.44 hour 20.1 We did not found any optical counterpart in the error box of the XRTcandidate (Page et al. GCN 41359). Magnitudes were estimated with the PanSTARRS cat. and are not corrected for galactic dust extinction. Our observations are consistent with other already reported Jelinek et al. (GCN 41355), Gill et al. (GCN 41356), Corcoran et al. (GCN 41370). The message may be cited. View this GCN Circular online at https://gcn.nasa.gov/circulars/41388. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39448] GRB250814A: TRT optical upper limits
by GCN Circulars 15 Aug '25

15 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41387 SUBJECT: GRB250814A: TRT optical upper limits DATE: 25/08/15 09:39:01 GMT FROM: sqjiang at NAOC <sqjiang(a)bao.ac.cn> S.Q. Jiang (NAOC), K. Noysena, K. Chanchaiworawit, S. Tinyanont (NARIT), L.B. He, J. An, X. Liu, Z.P. Zhu, D. Xu (NAOC), S. Y. Fu (HUST) report on behalf of a large collaboration: We observed the field of GRB 250814A detected by Swift (Caputo et al., GCN 41358) and Fermi (Fermi GBM team, GCN 41357), using the 0.7-m telescope of the Thai Robotic Telescope network (TRT), located at Sierra Remote Observatories in California. We obtained several 180 s frames in the R and I filters. The observation started at 07:44:15.35 UTC on 2025-08-14, i.e., 9.27 mins after the Swift/BAT trigger time. No new optical source is detected within the Swift/XRT enhanced error circle (Caputo et al., GCN 41358) down to R > 20.7 and I > 19.7 at about 17.3 mins post-burst, calibrated with nearby Pan-STARRS DR2 stars and not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/41387. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39447] GRB 250814B: SVOM/GRM observation
by GCN Circulars 15 Aug '25

15 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41386 SUBJECT: GRB 250814B: SVOM/GRM observation DATE: 25/08/15 09:29:26 GMT FROM: Chenwei Wang at IHEP <cwwang(a)ihep.ac.cn> SVOM/GRM team: Chen-Wei Wang, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Hui Yang (IRAP), Stéphane Schanne (CEA) Report on behalf of the SVOM team: SVOM/GRM was triggered on-ground by GRB 250814B at 2025-08-14T10:22:10.500 UTC (T0), which is also detected by Fermi/GBM (Fermi GBM Team, GCN #41366). With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of a single pulse with a T90 of 9.0 +2.0/-3.0 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb250814B.png The SVOM/GRM on-ground localization of this burst is (J2000): RA: 73.9 deg DEC: 22.2 deg Error: 7.1 deg (1sigma, statistical only) We caution that the calibration of SVOM/GRM is undergoing and this localization is subject to systematic errors. The SVOM/GRM on-ground localization is consistent with Fermi/GBM (Fermi GBM Team, GCN #41366) In addition, the position of this burst, as determined by SVOM/GRM, is located at about 71 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view, and is consistent with no indication for subthreshold targets either from CRT and IMT of ECLAIRs. With this localization, the time-averaged spectrum from T0-5 to T0+7 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.46 +0.16/-0.22 and the cutoff energy, parameterized as Epeak, is 250 +395/-91 keV. The event fluence (10-1000 keV) in this time interval is (2.99 +0.43/-0.41)E-06 erg/cm^2. Thus GRB 250814B is consistent with Type II GRBs in the 'Amati' relation diagram, as shown at: https://www.bursthub.cn//admin/static/grb250814B_amati.png The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. GRM is developed by the Institute of High Energy Physics (IHEP) of CAS. The SVOM point of contact for this burst is: Chen-Wei Wang (IHEP)(cwwang(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/41386. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39446] GRB 250814C: SVOM/GRM observation of a short burst
by GCN Circulars 15 Aug '25

15 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41385 SUBJECT: GRB 250814C: SVOM/GRM observation of a short burst DATE: 25/08/15 09:18:33 GMT FROM: Chenwei Wang at IHEP <cwwang(a)ihep.ac.cn> SVOM/GRM team: Chen-Wei Wang, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Hui Yang (IRAP), Stéphane Schanne (CEA) Report on behalf of the SVOM team: SVOM/GRM was triggered in-flight by a short burst GRB 250814C (SVOM trigger reference: sb25081402) at 2025-08-14T03:24:23.000 UTC (T0), which is also detected by Konus-Wind and Swift/BAT. With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of multi-pulses with a T90 of 1.20 +0.20/-0.30 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb250814C.png There is no indication of any subthreshold target from both CRT and IMT triggers onboard ECLAIRs close to the time of this event, suggesting that it is either too weak to be detected or outside the FoV of ECLAIRs. The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. GRM is developed by the Institute of High Energy Physics (IHEP) of CAS. The SVOM point of contact for this burst is: Chen-Wei Wang (IHEP)(cwwang(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/41385. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39445] LIGO/Virgo/KAGRA S250813k: Swift XRT observations, 2 X-ray sources
by GCN Circulars 15 Aug '25

15 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41384 SUBJECT: LIGO/Virgo/KAGRA S250813k: Swift XRT observations, 2 X-ray sources DATE: 25/08/15 07:26:06 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> K.L. Page (U. Leicester), P.A. Evans (U. Leicester), J.A. Kennea (PSU), A. Tohuvavohu (U. Toronto), S.B. Cenko (NASA/GSFC), R.A.J. Eyles-Ferris (U. Leicester), A.P. Beardmore (U. Leicester), M.G. Bernardini (INAF-OAB), A.A. Breeveld (UCL-MSSL), S. Campana (INAF-OAB), J.J. Delaunay (PSU), M. De Pasquale (University of Messina), S. Dichiara (PSU), P. D’Avanzo (INAF-OAB), A. D’Aì (INAF-IASFPA) , V. D’Elia (ASI-SSDC & INAF-OAR), C. Gronwall (PSU), D. Hartmann (Clemson University), N. Klingler (NASA-GSFC / UMBC / CRESST II), N.P.M. Kuin (UCL-MSSL), S. Laha (NASA/GSFC), S.R. Oates (U. Birmingham), J.P. Osborne (U. Leicester), P. O’Brien (U. Leicester), M.J. Page (UCL-MSSL), G. Raman (PSU) S. Ronchini (PSU), T. Sbarrato (INAF-OAB), B. Sbarufatti (INAF-OAB), M.H. Siegel (PSU), G. Tagliaferri (INAF-OAB), E. Troja (U Tor Vergata, INAF) report on behalf of the Swift team: Swift has carried out 109 observations of the LVK error region for the GW trigger S250813k convolved with the 2MPZ catalogue (Bilicki et al. 2014, ApJS, 210, 9), using the 'BAYESTAR' (version BAYESTAR.fits.gz) GW localisation map. As this is a 3D skymap, galaxy distances were taken into account in selecting which ones to observe. The observations currently span from 2.0 ks to 164 ks after the LVK trigger, and the XRT has covered 7.9 deg^2 on the sky (corrected for overlaps). This covers 70% of the probability in the 'ligo-skymap-from-samples' (version ligo-skymap-from-samples.fits.gz) skymap, and 71% after convolving with the 2MPZ galaxy catalogue, as described by Evans et al. (2016, MNRAS, 462, 1591). We have detected 2 X-ray sources. Each source is assigned a rank of 1-4 which describes how likely it is to be related to the GW trigger, with 1 being the most likely and 4 being the least likely. The ranks are described at https://www.swift.ac.uk/ranks.php. We have found: * 0 sources of rank 1 * 0 sources of rank 2 * 1 source of rank 3 * 1 source of rank 4 RANK 3 sources ============== These are uncatalogued X-ray sources, however they are not brighter than previous upper limits, so do not stand out as likely counterparts to the GW trigger. | Source ID | RA | Dec | Err90 | Detection Flag | | S250813k_X12 | 08h 54m 56.80s | +71d 23' 19.9" | 8.3" | GOOD | RANK 4 sources ============== These are catalogued X-ray sources, showing no signs of outburst compared to previous observations, so they are not likely to be related to the GW trigger. | Source ID | RA | Dec | Err90 | Detection Flag | | S250813k_X11 | 09h 17m 14.09s | +75d 30' 53.0" | 7.1" | GOOD | For all flux conversions and comparisons with catalogues and upper limits from other missions, we assumed a power-law spectrum with NH=3x10^20 cm^-2, and photon index (Gamma)=1.7, unless otherwise stated. The results of the XRT automated analysis, including details of the sources listed above, are online at https://www.swift.ac.uk/LVC/S250813k This circular is an official product of the Swift XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/41384. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39444] GRB 250813B: SVOM/GRM observation
by GCN Circulars 15 Aug '25

15 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41383 SUBJECT: GRB 250813B: SVOM/GRM observation DATE: 25/08/15 07:23:53 GMT FROM: tanwj(a)ihep.ac.cn SVOM/GRM team: Wen-Jun Tan, Chen-Wei Wang, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Stéphane Schanne Report on behalf of the SVOM team: SVOM/GRM was triggered in-flight by GRB 250813B (SVOM burst-id sb25081303) at 2025-08-13T22:51:12UTC (T0), which is also detected by SVOM/ECLAIRs (W.J. XIE et al., GCN #41354), Swift-XRT (K.L. Page et al., GCN #41359), EP-FXT (Q. Y. Wu et al., GCN #41361), SVOM/MXT (D. Götz et al., GCN #41368) and FERMI/GBM (Jacob Smith et al., GCN #41376) With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of multiple pulses with a T90 of 24.9 +/-0.76 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb250813B.png With this localization given by SVOM/ECLAIRs (RA= 336.728, DEC= 12.498, GCN #41354), the time-averaged spectrum from T0-6 to T0+35 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -0.84 +/-0.07 and the cutoff energy, parameterized as Epeak, is 109 +6/-5 keV. The event fluence (10-1000 keV) in this time interval is (1.35 +/-0.20)E-05 erg/cm^2. With the redshift z = 1.752 by VLT/X-shooter (B. Schneider et al., GCN#41363), the Eiso (from 1 keV to 10 MeV in rest frame) of this burst is (1.16 +0.20/-0.18)E53 erg. GRB 250813B is consistent with Type II GRBs in the 'Amati' relation diagram, as shown at: https://www.bursthub.cn//admin/static/grb250813B_amati.png The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. GRM is developed by the Institute of High Energy Physics (IHEP) of CAS. The SVOM point of contact for this burst is: Wen-Jun Tan (IHEP)(tanwj(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/41383. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39443] GRB 250814A: P200/WIRC observations of the afterglow candidate
by GCN Circulars 15 Aug '25

15 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41382 SUBJECT: GRB 250814A: P200/WIRC observations of the afterglow candidate DATE: 25/08/15 06:11:05 GMT FROM: Tomas Ahumada Mena at Caltech <tahumada(a)caltech.edu> Tomás Ahumada (Caltech), Viraj Karambelkar (Caltech), Mansi Kasliwal (Caltech), Iver Warburton (Yale), Alessandro Peca (Yale), and Vishwajeet Swain (IITB) report: We observed the field of the Fermi and Swift GRB 250814A (Fermi team, GCN Circ. 41357; Caputo et al., GCN Circ. 41358, Salvaggio et al. GCN Circ. 41379), which is spatially coincident with the sub-threshold GW trigger S250814bg (GCN Circ. 41364), in the near-infrared J and Ks bands using the Wide-field Infrared Camera (WIRC; Wilson et al. 2003) on the Palomar 200-inch telescope. Observations began on 2025-08-15 at 03:20 UT and consisted of 1350 s in the Ks band, followed by J-band imaging starting at 04:00 UT with a total exposure time of 1200 s. We clearly detect the source announced in Karambelkar et al. (GCN Circ. 41337) and observed in i-band by Castro-Tirado et al. (GCN Circ. 41381) at RA = 20:25:13.9, Dec = +48:23:55.9 (J2000), in both bands. This position is consistent with the enhanced X-ray position reported by Salvaggio et al. (GCN Circ. 41379). Aperture photometry yields: Ks = 21.3 ± 0.2 mag (AB) J = 21.72 ± 0.15 mag (AB) These values are consistent, within the uncertainties, with those reported in Karambelkar et al. (GCN Circ. 41337) in both bands. We therefore conclude that this source shows no significant variability and is likely unrelated to the GRB. View this GCN Circular online at https://gcn.nasa.gov/circulars/41382. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39442] GRB 250814A: possible optical afterglow candidate at Spanish observatories
by GCN Circulars 15 Aug '25

15 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41381 SUBJECT: GRB 250814A: possible optical afterglow candidate at Spanish observatories DATE: 25/08/15 00:40:01 GMT FROM: I. Perez-Garcia at Institute of Astrophysics of Andalusia <ipg(a)iaa.es> A.J. Castro-Tirado, I. Perez-Garcia, F. J. Aceituno, M. D. Caballero-Garcia, S. Guziy, R. Sanchez-Ramirez, E. Fernandez-Garcia, S.-Y. Wu (IAA-CSIC), Y.-D. Hu (GXU), J. Becerra (IAC), M. Gritsevich (Univ. of Helsinki), A. Sintes (Univ. Illes Balears), J. A. Font (Univ. de Valencia), S. B. Pandey (ARIES), B.-B. Zhang (NJU), J. Flores (CAHA), D. Garcia (GTC, IAC) and A. Romero (GTC), on behalf of a larger collaboration, report: We initially observed the field of the GRB 250814A detected by both Fermi (Fermi GBM team, GCNC 41357) and Swift (Caputo et al. GCNC 41358) using the 1.5m OSN telescope at Observatorio de Sierra Nevada in Granada (clear filter, starting on Aug 14, 20:30 UT). In addition to this facility, we also used both the 2.2m telescope at the Calar Alto Observatory (z-band, starting at 21:55 UT) and the 10.4 GTC telescope (griz-band, starting on Aug 15, 00:00 UT). This event was proposed to be temporally and spatially coincident with the subthreshold GW trigger S250814bg (the LVK Collaboration, GCNC 41364), which occurred 3.7 s prior to the Fermi GBM trigger (de Barra et al., GCNC 41378). At the position of the X-ray afterglow detected by Swift/XRT (Salvaggio et al. GCNC 41379), we identify an optical source in our data (in particular on the GTC i-band image) at coordinates (J2000): RA = 20:25:13.87 Dec = +48:23:56.5 (+/- 0.5"), for which we measure i = 23.3 +/- 0.3, which could be the optical counterpart to GRB250814A. This object is consistent with the proposed NIR candidate (Karambelkar et al. GCNC 41377). Further optical observations would be needed in order to confirm whether this object is the electromagnetic counterpart to S250814bg. View this GCN Circular online at https://gcn.nasa.gov/circulars/41381. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39441] GRB 250814A: KAIT optical upper limit
by GCN Circulars 14 Aug '25

14 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41380 SUBJECT: GRB 250814A: KAIT optical upper limit DATE: 25/08/14 22:30:47 GMT FROM: Weikang Zheng at UC Berkeley <weikang(a)berkeley.edu> WeiKang Zheng (UCB) and Alexei V. Filippenko (UCB) report on behalf of the KAIT GRB team: The 0.76-m Katzman Automatic Imaging Telescope (KAIT), located at Lick Observatory, observed the field of GRB 250814A (Fermi GBM team, GCN 41357; Caputo et al., GCN 41358) starting at 07:50:38, Aug. 14 UT, 939 seconds after the burst. A set of 120x60s clear (roughly R) filter images were obtained. Preliminary analysis do not reveal any new optical counterpart candidate within the Swift/XRT error circles (Caputo et al., GCN 41358), neither in single image, nor in the co-add images. Also no object was found at the afterglow candidate position reported by Karambelkar et al. (GCN 41377). Our upper limit is about 21.5 (Vega) mag at a mid time of 1.27 hours after the burst. Our result is consistent with the upper limit reported by other groups (Becerra et al., GCN 41362; Postigo et al., GCN 41367; Karambelkar et al., GCN 41372; Salazar et al., GCN 41375). View this GCN Circular online at https://gcn.nasa.gov/circulars/41380. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39440] GRB 250814A: Swift-XRT refined Analysis
by GCN Circulars 14 Aug '25

14 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41379 SUBJECT: GRB 250814A: Swift-XRT refined Analysis DATE: 25/08/14 21:31:37 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> C. Salvaggio (INAF-OAB), M. Ferro (INAF-OAB), S. Dichiara (PSU), J.A. Kennea (PSU), D.N. Burrows (PSU), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), R. Brivio (INAF-OAB) and P.A. Evans report on behalf of the Swift-XRT team: We have analysed 6.7 ks of XRT data for GRB 250814A, from 163 s to 40.1 ks after the trigger. The data comprise 184 s in Windowed Timing (WT) mode (the first 10 s were taken while Swift was slewing) with the remainder in Photon Counting (PC) mode. The best available XRT position (using the promptly downlinked event data, the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue) is RA, Dec = 306.30792, 48.39903 which is equivalent to: RA (J2000): 20h 25m 13.90s Dec(J2000): +48d 23' 56.5" with an uncertainty of 2.2 arcsec (radius, 90% confidence). The light curve can be modelled with an initial power-law decay with an index of alpha=1.49 (+0.27, -0.28), followed by a break at T+338 s to an alpha of 3.15 (+0.26, -0.20). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 1.33 (+0.24, -0.22). The best-fitting absorption column is 1.2 (+0.4, -0.3) x 10^22 cm^-2, in excess of the Galactic value of 6.5 x 10^21 cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 1.9 (+/-0.4) and a best-fitting absorption column of 1.0 (+0.4, -0.3) x 10^22 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 5.5 x 10^-11 (9.3 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 1.0 (+0.4, -0.3) x 10^22 cm^-2 Galactic foreground: 6.5 x 10^21 cm^-2 Excess significance: 1.8 sigma Photon index: 1.9 (+/-0.4) If the light curve continues to decay with a power-law decay index of 3.15, the count rate at T+24 hours will be 1.3 x 10^-7 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 7.0 x 10^-18 (1.2 x 10^-17) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01342439. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/41379. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39439] GRB 240814A: Fermi GBM Observation
by GCN Circulars 14 Aug '25

14 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41378 SUBJECT: GRB 240814A: Fermi GBM Observation DATE: 25/08/14 20:20:15 GMT FROM: Cuán de Barra at UCD <cuan.debarra(a)ucdconnect.ie> C. de Barra (University College Dublin), P. McDermott (University College Dublin), and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 07:35:09.28 UT on 14 August 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250814A (trigger 776849714/250814316) which was also detected by Swift BAT (R. Caputo et al. 2025, GCN 41358). The Fermi GBM on-ground location is consistent with the Swift BAT position. The GBM trigger was temporally coincident with the non-significant compact binary merger candidate S250814bg (LVK Collaboration, GCN 41364) with GBM triggering 3.7s after S250814bg. The angle from the Fermi LAT boresight is 25 degrees. The GBM light curve consists of a single emission episode with a duration (T90) of about 22 s (50-300 keV). The time-averaged spectrum from T0-6.1 to T0+16.4 s is best fit by a simple power law function with index -1.63 +/- 0.04.The spectrum is equally well fit by a power law function with an exponential high-energy cutoff. The power law index is -1.15+/- 0.15 and the cutoff energy, parameterized as Epeak, is 132 +/- 24 keV. The event fluence (10-1000 keV) in this time interval is (2.9 +/- 0.2)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0+3.6 s in the 10-1000 keV band is 1.4 +/- 0.2 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog: https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html For Fermi GBM data and info, please visit the official Fermi GBM Support Page: https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/" View this GCN Circular online at https://gcn.nasa.gov/circulars/41378. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39438] GRB 250814A: Possible afterglow candidate from P200/WIRC
by GCN Circulars 14 Aug '25

14 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41377 SUBJECT: GRB 250814A: Possible afterglow candidate from P200/WIRC DATE: 25/08/14 19:35:32 GMT FROM: Viraj Karambelkar at Indian Inst of Tech,Bombay <karambelkarvraj21197(a)gmail.com> Viraj Karambelkar (Caltech), Mansi Kasliwal (Caltech), Steven Giacalone (Caltech), Emily Gilbert (IPAC), Matt Lastovka (UMD), Vishwajeet Swain (IITB), Gaurav Waratkar (IITB), Tomas Ahumada (Caltech) report: We observed the field of the Fermi and Swift GRB 250814A (Fermi team, GCN Circ. 41357, Caputo et al. GCN Circ. 41358) coincident with the sub-threshold GW trigger S250814bg (GCN Circ. 41364) in the near-infrared J and Ks bands with the Wide-field infrared Camera (WIRC, Wilson et al. 2003) on the Palomar 200-inch telescope. Observations started on 2025-08-14 at 11:31:29 UT and lasted for 1665 seconds in the J-band, and started at 12:09:12 UT and lasted for 810 seconds in the Ks-band. We marginally detect a faint source in the Ks-band image at RA=20:25:13.9, Dec=48:23:55.9 (J2000), ~0.6 arcsec from the enhanced position of the X-ray counterpart reported by Caputo et al (GCN 41358). We also detect a marginal source at this location in the more sensitive J-band image, however, it is blended with several faint sources and is near the detection limit of the image. We performed aperture photometry at the location of this source and measured the following magnitudes Ks ~ 21.2 +/- 0.35 mag (AB), J ~ 21.6 mag +/- 0.4 mag (AB) We encourage deep NIR observations to trace the brightness evolution and confirm the nature of this source. View this GCN Circular online at https://gcn.nasa.gov/circulars/41377. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39437] GRB 250813B: Fermi GBM Observation
by GCN Circulars 14 Aug '25

14 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41376 SUBJECT: GRB 250813B: Fermi GBM Observation DATE: 25/08/14 19:17:11 GMT FROM: Jacob Smith at Fermi-GBM Team <jrs0118(a)uah.edu> Jacob Smith (UAH) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team: At 22:51:11.24 UT on 13 August 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250813B (trigger 776818276/250813952), which was also detected by SVOM/ECLAIRs (W.J. Xie, et al. 2025, GCN 41354). The Fermi GBM on-ground location is consistent with the SVOM/ECLAIRs position. An optical afterglow was first reported by Ondrejov D50 (M. Jelinek, et al. 2025, GCN 41353) which also reports an extremely rapid decay (M. Jelinek, et al. 2025, GCN 41355). A redshift of z=1.752 was report by the VLT (B. Schneider, et al. 2025, GCN 41363). The angle from the Fermi LAT boresight is 99 degrees. The GBM light curve consists of multiple emission episodes with a duration (T90) of about 24.1 s (50-300 keV). The time-averaged spectrum from T0-3.8 to T0+31.0 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -0.82 +/- 0.04 and the cutoff energy, parameterized as Epeak, is 114 +/- 3 keV. A Band function fits equally well with Epeak = 112 +/- 4, alpha = -0.81 +/- 0.04, and beta = -3.67 +/- 0.79. The event fluence (10-1000 keV) in this time interval is (1.30 +/- 0.02)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+11 s in the 10-1000 keV band is 8.1 +/- 0.3 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog: https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html For Fermi GBM data and info, please visit the official Fermi GBM Support Page: https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/ View this GCN Circular online at https://gcn.nasa.gov/circulars/41376. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39436] GRB 250814A: Optical observations with MDM Hiltner 2.4m telescope
by GCN Circulars 14 Aug '25

14 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41375 SUBJECT: GRB 250814A: Optical observations with MDM Hiltner 2.4m telescope DATE: 25/08/14 18:24:24 GMT FROM: Janet Chen at National Central University <janetstars(a)gmail.com> L. E. Salazar Manzano (Umich), H.-W. Lin (UMich), A. Aryan, T.-W. Chen (both NCU), and S. Yang (HNAS) report: We observed the field of the GRB 250814A (Fermi GBM team, GCN41357) using the 2.4m Hiltner telescope (HT) at the Michigan-Dartmouth-MIT (MDM) Observatory in Arizona, United States. The Swift-XRT detection of GRB 250814A was proposed to be temporally and spatially coincident with the subthreshold GW trigger S250814bg, which occurred 6 s after the BAT trigger (Caputo et al., GCN41358). The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration, with the Fermi GBM team and Swift team, reported the identification of a GW candidate possibly associated with this GRB (GCN41364). The first epoch of observations started at 10:22 UTC on the 14th of August 2025 (MJD = 60901.432), 2.79 hr after the Swift trigger. We do not find any credible evidence of a new and uncataloged source in the difference images (subtraction using the Pan-STARRS1 template images) within the 2.2 arcseconds uncertainty circle of Swift-XRT localization. We utilized the Python-based package AutoPhOT (Brennan & Fraser, 2022, A&A, 667, A62) to perform template subtraction using the 'hotpants' (Becker A., 2015, ascl.soft. ascl:1504.004) algorithm and perform the PSF photometry. The details of the observations and the measured 3-sigma upper limits (in the AB system) are as follows: Telescope | Filter | MJD (start) | t-t0 (hr) | Exposure (s) | Magnitude | avg. Seeing 2.4m HT | g | 60901.432 | 2.79 | 300 * 5 | > 22.03 | 1".32 2.4m HT | r | 60901.436 | 2.88 | 300 * 7 | > 22.98 | 0".99 2.4m HT | i | 60901.462 | 3.51 | 300 * 4 | > 21.96 | 1".21 Our (detection) limits are consistent with those reported by Becerra et al. (GCN41362), Postigo et al. (GCN41367), and Karambelkar et al. (GCN41372). The presented magnitudes are calibrated using the field stars from the PanStarrs1 catalog and are not corrected for the expected Galactic foreground extinction corresponding to a reddening of A_g = 3.5 mag, A_r = 2.4 mag, and A_i = 1.8 mag in the direction of the transient (Schlafly & Finkbeiner 2011). View this GCN Circular online at https://gcn.nasa.gov/circulars/41375. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39435] Fermi trigger No 776818276: Global MASTER-Net observations report
by GCN Circulars 14 Aug '25

14 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41374 SUBJECT: Fermi trigger No 776818276: Global MASTER-Net observations report DATE: 25/08/14 16:14:45 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A.Sosnovskij (CrAO), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-Kislovodsk robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) started inspect of the Fermi GRB250813.95 (trigger No 776818276,22h 11m 00.00s , +19d 13m 58.8s, R=7.28) errorbox 2746 sec after notice time and 2777 sec after trigger time at 2025-08-13 23:37:29 UT, with upper limit up to 18.0 mag. The observations began at zenith distance = 34 deg. The sun altitude is -24.0 deg. The galactic latitude b = -30 deg., longitude l = 79 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2967904 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 2808 | 2025-08-13 23:37:29 | MASTER-Kislovodsk | (22h 08m 10.03s , +18d 25m 11.7s) | C | 60 | 17.7 | 2808 | 2025-08-13 23:37:29 | MASTER- | (22h 03m 28.88s , +18d 46m 39.1s) | C | 60 | 14.8 | 2984 | 2025-08-13 23:40:25 | MASTER-Kislovodsk | (22h 07m 29.43s , +20d 20m 47.2s) | C | 60 | 17.8 | 2984 | 2025-08-13 23:40:25 | MASTER- | (22h 02m 44.88s , +20d 42m 11.9s) | C | 60 | 14.9 | 3156 | 2025-08-13 23:43:17 | MASTER-Kislovodsk | (22h 10m 24.38s , +16d 32m 57.3s) | C | 60 | 17.5 | 3157 | 2025-08-13 23:43:17 | MASTER- | (22h 05m 45.98s , +16d 54m 29.9s) | C | 60 | 14.6 | 3339 | 2025-08-13 23:46:19 | MASTER-Kislovodsk | (22h 24m 10.71s , +18d 27m 26.3s) | C | 60 | 17.5 | 3339 | 2025-08-13 23:46:19 | MASTER- | (22h 19m 27.90s , +18d 49m 00.7s) | C | 60 | 14.5 | 3418 | 2025-08-13 23:47:39 | MASTER-Kislovodsk | (22h 08m 15.78s , +18d 25m 52.8s) | C | 60 | 17.9 | 3418 | 2025-08-13 23:47:39 | MASTER- | (22h 03m 36.62s , +18d 47m 14.6s) | C | 60 | 14.8 | 3591 | 2025-08-13 23:50:32 | MASTER-Kislovodsk | (22h 07m 30.54s , +20d 19m 04.2s) | C | 60 | 17.7 | 3591 | 2025-08-13 23:50:32 | MASTER- | (22h 02m 47.85s , +20d 40m 34.3s) | C | 60 | 14.7 | 3773 | 2025-08-13 23:53:33 | MASTER-Kislovodsk | (22h 10m 21.49s , +16d 31m 09.9s) | C | 60 | 17.6 | 3773 | 2025-08-13 23:53:33 | MASTER- | (22h 05m 44.59s , +16d 52m 43.6s) | C | 60 | 14.5 | 3853 | 2025-08-13 23:54:53 | MASTER-Kislovodsk | (22h 23m 41.95s , +20d 20m 32.4s) | C | 60 | 17.8 | 3853 | 2025-08-13 23:54:53 | MASTER- | (22h 18m 59.12s , +20d 42m 15.9s) | C | 60 | 14.7 | 3933 | 2025-08-13 23:56:13 | MASTER-Kislovodsk | (22h 08m 08.08s , +22d 13m 26.1s) | C | 60 | 17.7 | 3933 | 2025-08-13 23:56:13 | MASTER- | (22h 03m 21.71s , +22d 35m 08.2s) | C | 60 | 14.6 | 4012 | 2025-08-13 23:57:33 | MASTER-Kislovodsk | (22h 24m 09.79s , +18d 26m 53.9s) | C | 60 | 17.7 | 4012 | 2025-08-13 23:57:33 | MASTER- | (22h 19m 30.00s , +18d 48m 52.6s) | C | 60 | 14.4 | 4092 | 2025-08-13 23:58:53 | MASTER-Kislovodsk | (22h 08m 13.06s , +18d 25m 21.0s) | C | 60 | 17.9 | 4092 | 2025-08-13 23:58:53 | MASTER- | (22h 03m 32.84s , +18d 46m 59.0s) | C | 60 | 15.1 | 4172 | 2025-08-14 00:00:13 | MASTER-Kislovodsk | (22h 13m 51.74s , +14d 36m 31.5s) | C | 60 | 18.0 | 4172 | 2025-08-14 00:00:13 | MASTER- | (22h 09m 21.28s , +14d 57m 54.6s) | C | 60 | 14.4 | 4252 | 2025-08-14 00:01:33 | MASTER-Kislovodsk | (22h 07m 28.98s , +20d 18m 32.7s) | C | 60 | 17.8 | 4252 | 2025-08-14 00:01:33 | MASTER- | (22h 02m 45.07s , +20d 40m 23.5s) | C | 60 | 14.8 | 4332 | 2025-08-14 00:02:52 | MASTER-Kislovodsk | (22h 26m 12.78s , +16d 32m 27.6s) | C | 60 | 17.7 | 4332 | 2025-08-14 00:02:52 | MASTER- | (22h 21m 35.76s , +16d 54m 11.5s) | C | 60 | 14.6 | 5035 | 2025-08-14 00:14:36 | MASTER-Kislovodsk | (22h 10m 18.04s , +16d 32m 03.7s) | C | 60 | 17.6 | 5035 | 2025-08-14 00:14:36 | MASTER- | (22h 05m 43.29s , +16d 53m 37.3s) | C | 60 | 14.4 | 5115 | 2025-08-14 00:15:56 | MASTER-Kislovodsk | (22h 23m 41.08s , +20d 19m 17.0s) | C | 60 | 17.7 | 5115 | 2025-08-14 00:15:56 | MASTER- | (22h 18m 57.71s , +20d 41m 09.0s) | C | 60 | 14.7 | 5195 | 2025-08-14 00:17:15 | MASTER-Kislovodsk | (22h 08m 06.96s , +22d 11m 39.9s) | C | 60 | 17.6 | 5195 | 2025-08-14 00:17:15 | MASTER- | (22h 03m 22.97s , +22d 33m 19.9s) | C | 60 | 14.4 | 5275 | 2025-08-14 00:18:35 | MASTER-Kislovodsk | (22h 24m 14.86s , +18d 24m 30.7s) | C | 60 | 17.6 | 5275 | 2025-08-14 00:18:35 | MASTER- | (22h 19m 35.72s , +18d 46m 14.2s) | C | 60 | 14.6 | 5354 | 2025-08-14 00:19:55 | MASTER-Kislovodsk | (22h 08m 10.37s , +18d 25m 29.3s) | C | 60 | 17.8 | 5354 | 2025-08-14 00:19:55 | MASTER- | (22h 03m 35.00s , +18d 46m 54.5s) | C | 60 | 14.7 | 5434 | 2025-08-14 00:21:15 | MASTER-Kislovodsk | (22h 13m 55.03s , +14d 36m 10.9s) | C | 60 | 17.8 | 5434 | 2025-08-14 00:21:15 | MASTER- | (22h 09m 26.62s , +14d 57m 29.9s) | C | 60 | 14.4 | 5514 | 2025-08-14 00:22:35 | MASTER-Kislovodsk | (22h 07m 30.65s , +20d 19m 20.6s) | C | 60 | 17.8 | 5514 | 2025-08-14 00:22:35 | MASTER- | (22h 02m 51.61s , +20d 40m 54.7s) | C | 60 | 14.9 | 5594 | 2025-08-14 00:23:55 | MASTER-Kislovodsk | (22h 26m 09.86s , +16d 31m 01.7s) | C | 60 | 17.6 | 5594 | 2025-08-14 00:23:55 | MASTER- | (22h 21m 34.79s , +16d 52m 40.2s) | C | 60 | 14.6 | 5673 | 2025-08-14 00:25:14 | MASTER-Kislovodsk | (22h 10m 17.52s , +16d 31m 26.8s) | C | 60 | 17.7 | 5673 | 2025-08-14 00:25:14 | MASTER- | (22h 05m 43.53s , +16d 52m 58.7s) | C | 60 | 14.4 | 5753 | 2025-08-14 00:26:34 | MASTER-Kislovodsk | (22h 23m 41.53s , +20d 18m 44.5s) | C | 60 | 17.8 | 5753 | 2025-08-14 00:26:34 | MASTER- | (22h 19m 01.61s , +20d 40m 23.1s) | C | 60 | 14.8 | 5833 | 2025-08-14 00:27:53 | MASTER-Kislovodsk | (22h 08m 06.39s , +22d 11m 07.6s) | C | 60 | 17.7 | 5833 | 2025-08-14 00:27:53 | MASTER- | (22h 03m 23.24s , +22d 32m 45.0s) | C | 60 | 14.6 | 5913 | 2025-08-14 00:29:13 | MASTER-Kislovodsk | (22h 24m 14.63s , +18d 24m 10.0s) | C | 60 | 17.7 | 5913 | 2025-08-14 00:29:13 | MASTER- | (22h 19m 36.26s , +18d 45m 52.2s) | C | 60 | 14.5 | 5992 | 2025-08-14 00:30:33 | MASTER-Kislovodsk | (22h 08m 11.02s , +18d 24m 45.7s) | C | 60 | 17.9 | 5992 | 2025-08-14 00:30:33 | MASTER- | (22h 03m 36.46s , +18d 46m 08.9s) | C | 60 | 14.7 | 6072 | 2025-08-14 00:31:53 | MASTER-Kislovodsk | (22h 13m 55.87s , +14d 35m 37.3s) | C | 60 | 17.8 | 6072 | 2025-08-14 00:31:53 | MASTER- | (22h 09m 28.10s , +14d 56m 52.3s) | C | 60 | 14.4 | 6152 | 2025-08-14 00:33:12 | MASTER-Kislovodsk | (22h 07m 29.61s , +20d 18m 28.1s) | C | 60 | 17.8 | 6152 | 2025-08-14 00:33:13 | MASTER- | (22h 02m 51.28s , +20d 39m 56.7s) | C | 60 | 15.0 | 6232 | 2025-08-14 00:34:32 | MASTER-Kislovodsk | (22h 26m 07.82s , +16d 30m 36.5s) | C | 60 | 17.7 | 6232 | 2025-08-14 00:34:32 | MASTER- | (22h 21m 34.79s , +16d 52m 23.4s) | C | 60 | 14.3 | 6312 | 2025-08-14 00:35:53 | MASTER-Kislovodsk | (22h 10m 18.37s , +16d 30m 59.9s) | C | 60 | 17.8 | 6312 | 2025-08-14 00:35:53 | MASTER- | (22h 05m 47.66s , +16d 52m 15.6s) | C | 60 | 14.4 | 6392 | 2025-08-14 00:37:13 | MASTER-Kislovodsk | (22h 23m 40.10s , +20d 18m 20.1s) | C | 60 | 17.8 | 6392 | 2025-08-14 00:37:13 | MASTER- | (22h 18m 58.10s , +20d 40m 04.6s) | C | 60 | 14.9 | 6472 | 2025-08-14 00:38:32 | MASTER-Kislovodsk | (22h 08m 06.07s , +22d 10m 41.2s) | C | 60 | 17.7 | 6472 | 2025-08-14 00:38:32 | MASTER- | (22h 03m 21.72s , +22d 31m 59.9s) | C | 60 | 14.4 | 6552 | 2025-08-14 00:39:53 | MASTER-Kislovodsk | (22h 24m 15.13s , +18d 23m 33.6s) | C | 60 | 17.7 | 6552 | 2025-08-14 00:39:53 | MASTER- | (22h 19m 38.79s , +18d 45m 23.9s) | C | 60 | 14.0 | 6632 | 2025-08-14 00:41:13 | MASTER-Kislovodsk | (22h 08m 09.79s , +18d 24m 27.6s) | C | 60 | 17.9 | 6632 | 2025-08-14 00:41:13 | MASTER- | (22h 03m 35.86s , +18d 45m 46.2s) | C | 60 | 14.8 | 6712 | 2025-08-14 00:42:33 | MASTER-Kislovodsk | (22h 13m 55.82s , +14d 35m 22.4s) | C | 60 | 17.9 | 6712 | 2025-08-14 00:42:33 | MASTER- | (22h 09m 28.63s , +14d 56m 38.2s) | C | 60 | 14.3 | 6792 | 2025-08-14 00:43:53 | MASTER-Kislovodsk | (22h 07m 28.23s , +20d 18m 24.3s) | C | 60 | 17.9 | 6792 | 2025-08-14 00:43:53 | MASTER- | (22h 02m 50.64s , +20d 39m 51.8s) | C | 60 | 14.8 | 6872 | 2025-08-14 00:45:13 | MASTER-Kislovodsk | (22h 26m 07.62s , +16d 30m 11.5s) | C | 60 | 17.6 | 6872 | 2025-08-14 00:45:13 | MASTER- | (22h 21m 33.88s , +16d 51m 45.9s) | C | 60 | 14.6 | 6952 | 2025-08-14 00:46:33 | MASTER-Kislovodsk | (22h 10m 18.06s , +16d 30m 32.1s) | C | 60 | 17.6 | 6952 | 2025-08-14 00:46:33 | MASTER- | (22h 05m 45.53s , +16d 52m 01.0s) | C | 60 | 14.6 | 7032 | 2025-08-14 00:47:53 | MASTER-Kislovodsk | (22h 23m 40.75s , +20d 17m 53.8s) | C | 60 | 17.8 | 7032 | 2025-08-14 00:47:53 | MASTER- | (22h 18m 59.61s , +20d 39m 37.5s) | C | 60 | 14.8 | 7112 | 2025-08-14 00:49:13 | MASTER-Kislovodsk | (22h 08m 05.53s , +22d 10m 12.6s) | C | 60 | 17.6 | 7112 | 2025-08-14 00:49:13 | MASTER- | (22h 03m 23.89s , +22d 31m 42.7s) | C | 60 | 14.6 | 7192 | 2025-08-14 00:50:33 | MASTER-Kislovodsk | (22h 24m 13.75s , +18d 23m 04.7s) | C | 60 | 17.7 | 7192 | 2025-08-14 00:50:33 | MASTER- | (22h 19m 36.81s , +18d 44m 41.7s) | C | 60 | 14.8 | 7272 | 2025-08-14 00:51:53 | MASTER-Kislovodsk | (21h 58m 11.91s , +14d 35m 47.6s) | C | 60 | 17.1 | 7272 | 2025-08-14 00:51:53 | MASTER- | (21h 53m 44.26s , +14d 57m 09.2s) | C | 60 | 14.3 | 7352 | 2025-08-14 00:53:13 | MASTER-Kislovodsk | (22h 13m 54.38s , +14d 34m 46.8s) | C | 60 | 17.9 | 7352 | 2025-08-14 00:53:13 | MASTER- | (22h 09m 28.22s , +14d 56m 01.7s) | C | 60 | 14.3 | 7432 | 2025-08-14 00:54:32 | MASTER-Kislovodsk | (21h 51m 13.95s , +20d 16m 59.8s) | C | 60 | 17.4 | 7432 | 2025-08-14 00:54:32 | MASTER- | (21h 46m 38.71s , +20d 38m 21.3s) | C | 60 | 14.6 | 7512 | 2025-08-14 00:55:53 | MASTER-Kislovodsk | (22h 26m 08.99s , +16d 29m 45.1s) | C | 60 | 17.6 | 7512 | 2025-08-14 00:55:53 | MASTER- | (22h 21m 36.15s , +16d 51m 19.2s) | C | 60 | 14.4 | 7592 | 2025-08-14 00:57:13 | MASTER-Kislovodsk | (22h 24m 29.76s , +22d 12m 32.8s) | C | 60 | 17.7 | 7592 | 2025-08-14 00:57:13 | MASTER- | (22h 19m 44.77s , +22d 34m 21.0s) | C | 60 | 14.7 | 7672 | 2025-08-14 00:58:33 | MASTER-Kislovodsk | (22h 23m 39.23s , +20d 17m 28.4s) | C | 60 | 17.6 | 7672 | 2025-08-14 00:58:33 | MASTER- | (22h 19m 01.43s , +20d 38m 58.8s) | C | 60 | 14.6 | 7753 | 2025-08-14 00:59:54 | MASTER-Kislovodsk | (22h 08m 04.95s , +22d 09m 44.1s) | C | 60 | 17.5 | 7753 | 2025-08-14 00:59:54 | MASTER- | (22h 03m 24.14s , +22d 31m 12.8s) | C | 60 | 14.4 | 7833 | 2025-08-14 01:01:13 | MASTER-Kislovodsk | (22h 10m 22.60s , +24d 03m 48.3s) | C | 60 | 17.5 | 7833 | 2025-08-14 01:01:13 | MASTER- | (22h 05m 34.23s , +24d 25m 32.9s) | C | 60 | 14.4 | 7913 | 2025-08-14 01:02:33 | MASTER- | (21h 53m 44.89s , +14d 56m 38.4s) | C | 60 | 14.1 | 7913 | 2025-08-14 01:02:33 | MASTER-Kislovodsk | (21h 58m 11.67s , +14d 35m 15.6s) | C | 60 | 17.0 | 7994 | 2025-08-14 01:03:55 | MASTER- | (22h 09m 28.81s , +14d 55m 32.4s) | C | 60 | 13.9 | 7994 | 2025-08-14 01:03:55 | MASTER-Kislovodsk | (22h 13m 54.14s , +14d 34m 16.2s) | C | 60 | 17.5 | 8074 | 2025-08-14 01:05:15 | MASTER- | (21h 46m 41.03s , +20d 37m 52.8s) | C | 60 | 14.3 | 8074 | 2025-08-14 01:05:15 | MASTER-Kislovodsk | (21h 51m 15.27s , +20d 16m 32.0s) | C | 60 | 17.1 | 8154 | 2025-08-14 01:06:34 | MASTER- | (22h 21m 35.69s , +16d 50m 51.6s) | C | 60 | 14.1 | 8154 | 2025-08-14 01:06:34 | MASTER-Kislovodsk | (22h 26m 07.61s , +16d 29m 17.7s) | C | 60 | 17.4 | 8234 | 2025-08-14 01:07:55 | MASTER-Kislovodsk | (22h 24m 28.05s , +22d 12m 04.6s) | C | 60 | 17.3 | 8234 | 2025-08-14 01:07:55 | MASTER- | (22h 19m 46.63s , +22d 33m 41.3s) | C | 60 | 14.3 | 8314 | 2025-08-14 01:09:14 | MASTER-Kislovodsk | (21h 51m 45.60s , +22d 09m 33.8s) | C | 60 | 17.0 | 8314 | 2025-08-14 01:09:14 | MASTER- | (21h 47m 05.50s , +22d 31m 20.4s) | C | 60 | 13.6 | 8394 | 2025-08-14 01:10:34 | MASTER-Kislovodsk | (21h 52m 05.11s , +18d 20m 33.4s) | C | 60 | 16.8 | 8394 | 2025-08-14 01:10:34 | MASTER- | (21h 47m 32.62s , +18d 41m 59.4s) | C | 60 | 13.9 | 8474 | 2025-08-14 01:11:54 | MASTER-Kislovodsk | (22h 10m 22.92s , +24d 03m 22.1s) | C | 60 | 17.0 | 8474 | 2025-08-14 01:11:54 | MASTER- | (22h 05m 38.34s , +24d 24m 55.7s) | C | 60 | 14.1 | 8553 | 2025-08-14 01:13:14 | MASTER- | (21h 53m 45.59s , +14d 55m 58.9s) | C | 60 | 13.6 | 8553 | 2025-08-14 01:13:14 | MASTER-Kislovodsk | (21h 58m 11.28s , +14d 34m 35.2s) | C | 60 | 16.3 | 8633 | 2025-08-14 01:14:34 | MASTER-Kislovodsk | (21h 54m 27.28s , +16d 26m 39.4s) | C | 60 | 16.2 | 8633 | 2025-08-14 01:14:34 | MASTER- | (21h 49m 58.89s , +16d 48m 04.0s) | C | 60 | 13.6 | 8713 | 2025-08-14 01:15:54 | MASTER- | (21h 46m 40.88s , +20d 37m 02.6s) | C | 60 | 13.6 | 8713 | 2025-08-14 01:15:54 | MASTER-Kislovodsk | (21h 51m 13.90s , +20d 15m 43.3s) | C | 60 | 16.4 | 8793 | 2025-08-14 01:17:14 | MASTER-Kislovodsk | (22h 40m 07.00s , +18d 23m 20.2s) | C | 60 | 16.7 | 8793 | 2025-08-14 01:17:14 | MASTER- | (22h 35m 33.87s , +18d 44m 52.4s) | C | 60 | 13.4 | 8873 | 2025-08-14 01:18:34 | MASTER- | (22h 19m 45.64s , +22d 33m 33.4s) | C | 60 | 12.9 | 8873 | 2025-08-14 01:18:34 | MASTER-Kislovodsk | (22h 24m 27.35s , +22d 11m 33.6s) | C | 60 | 16.5 | 8953 | 2025-08-14 01:19:54 | MASTER-Kislovodsk | (21h 51m 43.82s , +22d 08m 58.9s) | C | 60 | 16.2 | 8953 | 2025-08-14 01:19:54 | MASTER- | (21h 47m 06.12s , +22d 30m 11.7s) | C | 60 | 13.2 | 9032 | 2025-08-14 01:21:13 | MASTER-Kislovodsk | (21h 52m 03.47s , +18d 19m 58.8s) | C | 60 | 16.0 | 9032 | 2025-08-14 01:21:13 | MASTER- | (21h 47m 34.22s , +18d 41m 19.5s) | C | 60 | 13.3 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. View this GCN Circular online at https://gcn.nasa.gov/circulars/41374. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39434] Swift GRB250814.32: Global MASTER-Net observations report
by GCN Circulars 14 Aug '25

14 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41373 SUBJECT: Swift GRB250814.32: Global MASTER-Net observations report DATE: 25/08/14 16:14:43 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A.Sosnovskij (CrAO), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-Tunka robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Russia (Applied Physics Institute, Irkutsk State University) was pointed to the Swift GRB250814.32 (trigger No 1342439,20h 25m 18.96s , +48d 23m 27.6s, R=0.05) errorbox 28681 sec after notice time and 28770 sec after trigger time at 2025-08-14 15:34:30 UT, with upper limit up to 16.4 mag. The observations began at zenith distance = 6 deg. The sun altitude is -21.4 deg. The galactic latitude b = 6 deg., longitude l = 85 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2968157 We obtain a following upper limits. Tmid-T0 | Site |Filt.| Expt. | Limit| Comment _________|_____________________|_____|_______|______|________ 28860 | MASTER-Tunka | C | 180 | 16.4 | 28860 | MASTER- | C | 180 | 16.3 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. View this GCN Circular online at https://gcn.nasa.gov/circulars/41373. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39433] GRB 250814A: J-band upper limit from WINTER
by GCN Circulars 14 Aug '25

14 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41372 SUBJECT: GRB 250814A: J-band upper limit from WINTER DATE: 25/08/14 15:52:22 GMT FROM: Viraj Karambelkar at Indian Inst of Tech,Bombay <karambelkarvraj21197(a)gmail.com> Viraj Karambelkar (Caltech), Tomas Ahumada (Caltech), Benjamin Schneider (LAM), Robert Stein (UMD), Geoffrey Mo (MIT), Danielle Frostig (CfA), Nathan Lourie (MIT), Robert Simcoe (MIT), and Mansi Kasliwal (Caltech) report: We observed the field of the Fermi and Swift GRB 250814A (Fermi team, GCN Circ. 41357, Caputo et al. GCN Circ. 41358) coincident with the sub-threshold GW trigger S250814bg (GCN Circ. 41364) in the near-infrared with the Palomar 1-m telescope, equipped with the 1-square degree WINTER camera (Lourie et al. 2020, Frostig et al. 2024). Observations started on 2025-08-14 at 07:49:52 UT (15 min after the trigger) and consisted of 15 exposures of 120 s in the J-band. In the stacked image, we do not detect any new source at the X-ray afterglow position reported by Caputo et al, GCN 41358 down to the following 5-sigma AB magnitude: J > 19.3 The images were processed using the WINTER data reduction pipeline implemented with mirar (https://github.com/winter-telescope/mirar, https://doi.org/10.5281/zenodo.13352565) The photometric calibration was performed using nearby stars from the 2MASS catalog and the magnitude is not corrected for Galactic extinction. WINTER (Wide-field INfrared Transient ExploreR) is a partnership between MIT and Caltech, housed at Palomar Observatory, and funded by NSF MRI, NSF AAG, the David and Lucile Packard Foundation, and the MIT Kavli Institute for Astrophysics and Space Research. View this GCN Circular online at https://gcn.nasa.gov/circulars/41372. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39432] IceCube-250813A: Upper limits from a search for additional neutrino events in IceCube
by GCN Circulars 14 Aug '25

14 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41371 SUBJECT: IceCube-250813A: Upper limits from a search for additional neutrino events in IceCube DATE: 25/08/14 13:42:34 GMT FROM: Alicia Mand at IceCube/UW-Madison <aemand(a)wisc.edu> The IceCube Collaboration (http://icecube.wisc.edu/) reports: IceCube has performed a search [1] for additional track-like muon neutrino events arriving from the direction of IceCube-250813A (https://gcn.nasa.gov/circulars/41338) in a time range of 1000 seconds centered on the alert event time (2025-08-13 03:12:49.690 UTC to 2025-08-13 03:29:29.690 UTC) during which IceCube was collecting good quality data. Excluding the event that prompted the alert, zero track-like events are found within the 90% containment region of IceCube-250813A. We report a p-value of 1.00 in this time window. The IceCube sensitivity to neutrino point sources with an E^-2.5 spectrum (E^2 dN/dE at 1 TeV) within the locations spanned by the 90% spatial containment region of IceCube-250813A is 1.3e-01 GeV cm^-2 in a 1000 second time window. 90% of events IceCube would detect from a source at this declination with an E^-2.5 spectrum have energies in the approximate energy range between 2e+02 GeV and 1e+05 GeV. A subsequent search was performed including 2 days of data centered on the alert event time (2025-08-12 03:21:09.690 UTC to 2025-08-14 03:21:09.690 UTC). In this case, we report a p-value of 1.00, consistent with no significant excess of track events. The IceCube sensitivity to neutrino point sources with an E^-2.5 spectrum (E^2 dN/dE at 1 TeV) within the locations spanned by the 90% spatial containment region of IceCube-250813A is 1.5e-01 GeV cm^-2 in a 2 day time window. The IceCube Neutrino Observatory is a cubic-kilometer neutrino detector operating at the geographic South Pole, Antarctica. The IceCube realtime alert point of contact can be reached at roc(a)icecube.wisc.edu. [1] IceCube Collaboration, R. Abbasi et al., ApJ 910 4 (2021) View this GCN Circular online at https://gcn.nasa.gov/circulars/41371. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39431] GRB 250813B: NOT observations of the optical afterglow
by GCN Circulars 14 Aug '25

14 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41370 SUBJECT: GRB 250813B: NOT observations of the optical afterglow DATE: 25/08/14 12:18:54 GMT FROM: Antonio Martin-Carrillo at UCD,Space Science Group <antonio.martin-carrillo(a)ucd.ie> G. Corcoran (UCD), A. Martin-Carrillo (UCD), D. B. Malesani (DAWN/NBI and Radboud), B. Schneider (LAM), B. P. Gompertz (Birmingham), V. Vuolteenaho (Univ. of Oulu), report on behalf of a larger collaboration: We observed the field of the SVOM/ECLAIRs GRB 250813B (Xie et al., GCN 41352; Xie et al., GCN 42354), using the ALFOSC camera mounted on the Nordic Optical Telescope (NOT). We obtained 6x150 s exposures in the r-band and 5x200 s in the z-band, starting at 2025-08-14 00:05:04 UT (1.231 hr after the trigger). The optical afterglow reported by Jelinek et al. (GCN 41355), de Ugarte Postigo et al. (GCN 41356), Schneider et al. (GCN 41363) and Xin et al. (GCN 41369) is well detected with a preliminary magnitude of r = 21.00 +/- 0.08 (AB, mid-time 1.379 hr after trigger); z = 20.04 +/- 0.09 (AB, mid-time 1.689 hr after trigger). The photometric calibration was performed using nearby stars from the Pan-STARRS catalog and the magnitudes are not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/41370. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39430] GRB 250813B: SVOM/VT optical observations
by GCN Circulars 14 Aug '25

14 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41369 SUBJECT: GRB 250813B: SVOM/VT optical observations DATE: 25/08/14 12:16:34 GMT FROM: Liping Xin at NAOC, SVOM <xlp(a)nao.cas.cn> L. P. Xin, H. L. Li, Y. L. Qiu, C. Wu, Y. N. Ma, Z. H. Yao, X. H. Han, J. Wang, Y. Xu, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA), B. T. Wang (YNAO) report on behalf of the SVOM/VT team. SVOM performed an automatic slew on the burst GRB 250813B triggered by SVOM/ECLAIRs (Xie et al., GCN 41354). SVOM/VT start the observations at 278 seconds after the burst, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. The optical counterpart (Jelinek et al., GCN 41353 & GCN 41355; Schneider et al., GCN 41363; de Ugarte Postigo et al., GCN 41356) at the position consistent with the locations of Swift/XRT (Page et al., GCN 41359), EP/FXT (Wu et al., GCN 41361) and SVOM/MXT(Xie et al., GCN 41354, Gotz et al., GCN 41368), was clearly detected in both VT_R and VT_B. During the X-band data available, the brightness was fading from VT_R=16.61+/0.02 mag and VT_B=17.73+/-0.03 mag at 303 seconds post the burst to VT_R=20.9+/-0.1 mag and VT_B=22.1+/-0.2 mag at 4.27 hours after the burst. Our photometry was not corrected for Galactic extinction. The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS. The SVOM point of contact for this burst is Wenjin Xie (xiewj(a)bao.ac.cn) Please contact the BA by email if you require additional information regarding the SVOM follow-up of this burst. View this GCN Circular online at https://gcn.nasa.gov/circulars/41369. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39429] Subject GRB 250813B: SVOM/MXT refined analysis
by GCN Circulars 14 Aug '25

14 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41368 SUBJECT: Subject GRB 250813B: SVOM/MXT refined analysis DATE: 25/08/14 11:45:54 GMT FROM: Diego Gotz at CEA <diego.gotz(a)cea.fr> D. Götz (CEA), F. Robinet (IJCLab), P. Maggi (ObAS), H. Goto (Kanazawa Univ./CEA), M. Moita (CEA), C. Plasse (CEA), , C. Van Hove (IJCLab) report of behalf of the SVOM/MXT Team: GRB 250813B (Xie et al. GCN 41352/41354) was observed by SVOM/MXT after an automatic SVOM slew, starting at T0 = 2025-08-13T22:54:01, 169 s after trigger time Tb. MXT observed for the remainder of the orbit, cumulating 188 s of useful data before entering Earth occultation. Using the full X-band dataset of the first orbit, the position of the MXT afterglow is refined to: R.A. (J2000) = 22h26m58.6s Dec (J2000) = +12d27m08s with a 90% C.L. radius of 54 arc sec (including 25 arcseconds systematic error added in quadrature). This position is at 47 arc sec from the optical counterpart reported in GCN 41353. The light curve exhibits an initial fast fading with temporal decay of -2.3+/-0.5. We analysed the early time (first orbit) spectrum and modelled it with a redshifted (z=1.75 GCN 41363) absorbed power-law, a photon index Gamma 1.4+-/0.3 at 90% C.L and a redshifted absorbing column of NH = <0.8x1e22 cm^-2 on top of a Galactic NH = 4.86x10^20 cm^-2. The source is still detected on the subsequent orbit between Tb+3900 and Tb+6100 s but not after. The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. MXT was developed jointly by CEA, CNES, University of Leicester, IJCLab and MPE. The SVOM point of contact for this burst is Wenjin Xie (xiewj(a)bao.ac.cn) Please contact the BA by email if you require additional information regarding the SVOM follow-up of this burst. View this GCN Circular online at https://gcn.nasa.gov/circulars/41368. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39428] GRB 250814A: COLIBRÍ optical upper limit
by GCN Circulars 14 Aug '25

14 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41367 SUBJECT: GRB 250814A: COLIBRÍ optical upper limit DATE: 25/08/14 11:04:35 GMT FROM: Antonio de Ugarte Postigo at LAM, CNRS <adeugartepostigo(a)gmail.com> Antonio de Ugarte Postigo (LAM), Ramandeep Gill (UNAM), Jean-Grégoire Ducoin (CPPM), Rosa L. Becerra (U Roma), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Fredd Alvarez (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (OCA), Nathaniel R. Butler (ASU) , Damien Dornic (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Benjamin Schneider (LAM): We imaged the field of the Fermi and Swift GRB 250814A (Fermi team, GCN Circ. 41357, Caputo et al. GCN Circ. 41358) using the DDRAGO wide-field imager on the COLIBRÍ telescope. We observed from 2025-08-14 07:48 to 08:07 UTC (from 13.9 to 33.0 minutes after the trigger) and obtained 16 minutes of exposure in the i filter. The data were reduced and coadded with the COLIBRÍ pipeline and analysed with STDWeb/STDPipe (Karpov 2025). The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction. In the stacked image, we do not detect any new source at the XRT source position (Caputo et al. GCN Circ. 41358) down to the following 3-sigma limit: i > 22.9 This upper limit is consistent with the one reported by Becerra et al. (GCN Circ. 41362). We thank the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir and the COLIBRÍ and DDRAGO engineering teams. COLIBRÍ is an astronomical observatory developed and operated jointly by France (AMU, CNES and CNRS) and Mexico (UNAM and SECIHTI). It is located at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, Mexico. View this GCN Circular online at https://gcn.nasa.gov/circulars/41367. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39427] GRB 250814B: Fermi GBM Final Real-time Localization
by GCN Circulars 14 Aug '25

14 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41366 SUBJECT: GRB 250814B: Fermi GBM Final Real-time Localization DATE: 25/08/14 10:32:39 GMT FROM: Fermi GBM Team at MSFC/Fermi-GBM <do_not_reply(a)GIOC.nsstc.nasa.gov> The Fermi GBM team reports the detection of a likely LONG GRB At 10:22:10 UT on 14 Aug 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250814B (trigger 776859735.510984 / 250814432). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 80.1, Dec = 24.6 (J2000 degrees, equivalent to J2000 05h 20m, 24d 36'), with a statistical uncertainty of 4.6 degrees. The angle from the Fermi LAT boresight is 132.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250814432/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250814432/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250814432/… View this GCN Circular online at https://gcn.nasa.gov/circulars/41366. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39426] GRB 250813A: AstroSat CZTI detection
by GCN Circulars 14 Aug '25

14 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41365 SUBJECT: GRB 250813A: AstroSat CZTI detection DATE: 25/08/14 10:31:51 GMT FROM: Gaurav Waratkar at IIT Bombay <gauravwaratkar(a)iitb.ac.in> M. Tembhurnikar (IUCAA), G. Waratkar (IITB), A. Vibhute (IUCAA), V. Bhalerao (IITB), D. Bhattacharya (Ashoka University/IUCAA), A. R. Rao (IUCAA/TIFR), and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration: Analysis of AstroSat CZTI data with the CIFT framework (Sharma et al., 2021, JApA, 42, 73) showed the detection of a GRB 250813A which was also detected by Fermi/GBM (Fermi GBM Team, GCN Circ. 41343). The source was faintly detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2025-08-13 01:46:01.50 UTC. The measured peak count rate associated with the burst is 72 (+35, -16) counts/s above the background in the combined data of all quadrants, with a total of 485 (+199, -228) counts. The local mean background count rate was 249 (+5, -6) counts/s. Using cumulative rates, we measure a T90 of 12 (+1, -6) s. The source was also faintly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve peaks at 2025-08-13 01:46:00.12 UTC. The measured peak count rate associated with the burst is 117 (+70, -10) counts/s above the background in the combined data of all quadrants, with a total of 1002 (+403, -457) counts. The local mean background count rate was 1144 (+8, -8) counts/s. We measure a T90 of 13 (+2, -4) s from the cumulative Veto light curve. CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, URSC, IUCAA, SAC, and PRL. The Indian Space Research Organisation funded, managed, and facilitated the project. CZTI GRB detections are reported regularly on the payload site at: http://astrosat.iucaa.in/czti/?q=grb View this GCN Circular online at https://gcn.nasa.gov/circulars/41365. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39425] LIGO/Virgo/KAGRA S250814bg: Identification of a GW compact binary merger candidate possibly associated with GRB 250814A detected by Fermi GBM and Swift BAT
by GCN Circulars 14 Aug '25

14 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41364 SUBJECT: LIGO/Virgo/KAGRA S250814bg: Identification of a GW compact binary merger candidate possibly associated with GRB 250814A detected by Fermi GBM and Swift BAT DATE: 25/08/14 10:31:50 GMT FROM: Sreeta Roy at University of Warsaw <sreeta.roy(a)ligo.org> The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration with the Fermi GBM team and Swift team report: We identified the compact binary merger candidate S250814bg during real-time processing of data from LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) at 2025-08-14 07:35:05.587 UTC (GPS time: 1439192123.587). The candidate was found by the GstLAL [1] analysis pipeline. Based on the analysis of gravitational-wave data alone, this candidate does not meet our criteria for a high-significance public alert as its false alarm rate is estimated by the online analysis to be 0.00012 Hz or about one in 2 hours. However, a search performed by the RAVEN pipeline found a significant coincidence between this candidate and Fermi GBM trigger with ID 776849714, which is associated with GRB 250814A. The event’s properties can be found at this URL: https://gracedb.ligo.org/superevents/S250814bg The classification of the GW signal, in order of descending probability, is Terrestrial (>99%), BBH (<1%), NSBH (<1%), or BNS (<1%). Excess noise was present in the L1 detector at the time of this candidate, which may affect the parameters or the significance of the candidate. Assuming the candidate is astrophysical in origin, the probability that at least one of the compact objects is consistent with a neutron star mass (HasNS) is <1%. [2] Using the masses and spins inferred from the signal, the probability of matter outside the final compact object (HasRemnant) is <1%. [2] Both HasNS and HasRemnant consider the support of several neutron star equations of state for maximum neutron star mass. The probability that either of the binary components lies between 3 and 5 solar masses (HasMassGap) is 3%. The source chirp mass falls with highest probability in the bin (22.0, 44.0) solar masses, assuming the candidate is astrophysical in origin. Two GW-only sky maps are available at this time and can be retrieved from the GraceDB event page: * bayestar.multiorder.fits,0, an initial localization generated by BAYESTAR [3], distributed via GCN and SCiMMA notices about 2 minutes after the candidate event time. * bayestar.multiorder.fits,1, an initial localization generated by BAYESTAR [3], distributed via GCN and SCiMMA notices about 6 minutes after the candidate event time. The preferred sky map at this time is bayestar.multiorder.fits,1. For the bayestar.multiorder.fits,1 sky map, the 90% credible region is 7867 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 13504 +/- 6537 Mpc (a posteriori mean +/- standard deviation). A search performed by the RAVEN pipeline [4] found a temporal coincidence between S250814bg and a Fermi GBM trigger with ID 776849714, which is associated with GRB 250814A (Fermi GBM Team, GCN Circular 41357). The GRB trigger time is 3.7 seconds after the GW candidate event. The estimated joint false alarm rate for the coincidence using just timing info before trials are applied is 7.5e-09 Hz, or about one in 4 years. Combined sky maps are also available: * combined-ext.multiorder.fits,0, an initial localization, distributed via GCN and SCiMMA notices about 2 minutes after the candidate event time. * combined-ext.multiorder.fits,1, an initial localization, distributed via GCN and SCiMMA notices about 6 minutes after the candidate event time. * combined-ext.multiorder.fits,2, an initial localization, distributed via GCN and SCiMMA notices about an hour after the candidate event time. For the combined-ext.multiorder.fits,2 sky map, the 90% credible region is 471 deg2. Considering the overlap of the individual sky maps, the estimated joint false alarm rate for the spatial and temporal coincidence before trials are applied is 1.5e-08 Hz, or about one in 2 years. After including the trials factor of 30, the joint false alarm rate becomes 4.5e-07 Hz, or about 14 per year. Moreover, the GW candidate is 6 seconds after the Swift-BAT trigger 1342439, associated with the same GRB 250814A (Swift Team, GCN Circular 41358). The Swift-BAT GRB is spatio-temporal coincident with the Fermi GBM one, therefore they can be reliably considered the same astrophysical event. Considering the Swift-BAT localization, the estimated joint false alarm rate between the Swift-BAT and the GW candidate for the spatial and temporal coincidence before trials are applied is 1.0e-08 Hz, or about one in 3 years. After including the trials factor of 30, the joint false alarm rate becomes 3.0e-07 Hz, or about 9 per year. For further information about analysis methodology and the contents of this alert, refer to the LIGO/Virgo/KAGRA Public Alerts User Guide https://emfollow.docs.ligo.org/. [1] Tsukada et al. PRD 108, 043004 (2023) doi:10.1103/PhysRevD.108.043004 and Ewing et al. PRD 109, 042008 (2024) doi:10.1103/PhysRevD.109.042008 [2] Chatterjee et al. ApJ 896, 54 (2020) doi:10.3847/1538-4357/ab8dbe [3] Singer & Price PRD 93, 024013 (2016) doi:10.1103/PhysRevD.93.024013 [4] Urban, A. L. 2016, Ph.D. Thesis https://dc.uwm.edu/etd/1218 and Piotrzkowski, B. J. 2022, Ph.D. Thesis https://dc.uwm.edu/etd/3060 View this GCN Circular online at https://gcn.nasa.gov/circulars/41364. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39424] GRB 250813B: VLT X-shooter spectroscopic redshift z = 1.752
by GCN Circulars 14 Aug '25

14 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41363 SUBJECT: GRB 250813B: VLT X-shooter spectroscopic redshift z = 1.752 DATE: 25/08/14 10:29:14 GMT FROM: Gregory Corcoran at University College Dublin <gregory.corcoran(a)ucdconnect.ie> B. Schneider (LAM), G. Corcoran (UCD), E. Le Floc’h (CEA), A. de Ugarte Postigo (LAM), J. An (NAOC), A. L. Thakur (INAF-IAPS), D. B. Malesani (DAWN/NBI and Radboud), A. Martin-Carrillo (UCD), N. R. Tanvir (U. Leicester) report on behalf of the Stargate collaboration: We observed the optical afterglow (Jelinek et al., GCN 41355; de Ugarte Postigo et al., GCN 41356) of GRB 250813B detected by SVOM/ECLAIRs (Xie et al., GCN 41352; Xie et al., GCN 42354) with ESO VLT UT3 (Melipal) equipped with the X-shooter spectrograph. In images taken with the acquisition camera on Aug 14 05:40 UT (6.82 hr after the ECLAIRs trigger), the optical afterglow is clearly detected in g, r, and z bands. We measured a preliminary magnitude r = 22.24 +/- 0.06 AB (calibrated against the Pan-STARRS PS1 catalog). Our spectra cover the wavelength range 3000-21000 AA, and consist of 4 exposures of 600 s each. Observations started on 2025-08-14 at approximately 05:50 UT (6.98 hr after the SVOM trigger). In a preliminary reduction of the spectra, we detect a faint continuum down to ~3590 AA at the blue end. From the detection of a multitude of absorption lines, which we interpret as due to C II, Si IV, Si II, C IV, C I, Al II, Al III, Mn I, Fe II, Fe II*, Mn II, Mg II, Mg I, Ca II, we infer a redshift of z = 1.752. We acknowledge excellent support from the ESO observing staff in Paranal, in particular Celia Desgrange, Rodrigo Romero, and Akke Corporaal. The analysis of this spectrum was carried out with the help of the zHunter tool (https://doi.org/10.5281/zenodo.15189495) View this GCN Circular online at https://gcn.nasa.gov/circulars/41363. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39423] GRB 250814A: DDOTI Optical Upper Limit
by GCN Circulars 14 Aug '25

14 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41362 SUBJECT: GRB 250814A: DDOTI Optical Upper Limit DATE: 25/08/14 10:26:15 GMT FROM: Rosa L. Becerra at Tor Vergata, Roma <rosa.becerra(a)roma2.infn.it> Rosa L. Becerra (U Roma), Alan M. Watson (UNAM), Sahil Atri (U Roma), Camila Angulo Valdez (UNAM), Nat Butler (ASU), Simone Dichiara (Penn State University), Tsvetelina Dimitrova (ASU), Alexander Kutyrev (GSFC/UMD), William H. Lee (UNAM), Océlotl López (UNAM), Margarita Pereyra (UNAM) and Eleonora Troja (U Roma) report: We observed the field of GRB 250814A detected by Swift/BAT (Caputo et al., GCN Circ. 41358) with the DDOTI/OAN wide-field imager at the Observatorio Astronómico Nacional on Sierra San Pedro Mártir (http://ddoti.astroscu.unam.mx) on the night of 2025-08-14 UTC. DDOTI observed the XRT position (Caputo et al., GCN Circ. 41358) from 08:50 UTC to 09:18 UTC (from T+ 1.3 h to T+ 1.7 h after the trigger) and obtained a total exposure of 24 minutes. Comparing our observations to the USNO-B1 and Pan-STARRS PS1 DR2 catalogues, we detect no uncatalogued fading sources within the observed field down to a 3-sigma limiting AB magnitude of: w > 19.6 This value is not corrected for the Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/41362. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39422] GRB 250813B: EP-FXT counterpart detection
by GCN Circulars 14 Aug '25

14 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41361 SUBJECT: GRB 250813B: EP-FXT counterpart detection DATE: 25/08/14 09:01:39 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Q. Y. Wu, H. Q. Cheng, Z. X. Ling (NAO, CAS) on behalf of the Einstein Probe (EP) team: EP-FXT performed a follow-up observation of the SVOM/ECLAIRs-detected burst GRB 250813B (SVOM/sb25081303, Xie et al. GCN #41352, #41354) at 2025-08-14 00:58:26(UTC), about 2 hours after the SVOM/ECLAIRs trigger, with an exposure time of ~1.3 ks. One uncatalogued source is detected within the ECLAIRs error circle, and the source is spatially consistent with the counterpart reported in optical and X-ray bands (Xie et al. GCN #41352, #41354, Jelinek et al. GCN #41353, #41355, Gill et al. GCN #41356, Page et al. GCN #41359). Preliminary analysis on this source are conducted (note that the exposure time for the analysed data is not complete), with the details listed as follows. Source 1: EPF_J222700.2+122741 RA (J2000): 336.7507 Dec (J2000): 12.4617 Flux: 1.00 x 10^-11 erg/s/cm2 (observed, 0.5-10 kev) Flux_err: 1.2 x 10^-12 erg/s/cm2 (90% C. L.) The position uncertainty of the source is about 10 arcsec in radius (90% C.L. statistical and systematic). Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). View this GCN Circular online at https://gcn.nasa.gov/circulars/41361. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39421] Fermi-LAT Gamma-ray Observations of IceCube-250813A
by GCN Circulars 14 Aug '25

14 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41360 SUBJECT: Fermi-LAT Gamma-ray Observations of IceCube-250813A DATE: 25/08/14 08:20:05 GMT FROM: Leo Pfeiffer at University of Würzburg <pfeiffer.leo(a)gmail.com> L. Pfeiffer (Univ. of Wuerzburg), S. Buson (DESY, Univ. of Wuerzburg), S. Garrappa (Weizmann Institute of Science) and C. Bartolini (INFN Bari) on behalf of the Fermi-LAT collaboration: We report an analysis of observations of the vicinity of the high-energy IC250813A neutrino event (GCN 41338) with all-sky survey data from the Large Area Telescope (LAT), on board the Fermi Gamma-ray Space Telescope. The IceCube event was detected on 2025-08-13 at 03:21:09.69 UTC (T0) with J2000 position RA = 275.36 (+0.84, -0.94) deg, Decl. = 8.27 (+0.79, -0.75) deg 90% PSF containment (J2000). No cataloged gamma-ray sources are found within the 90% IC250813A localization error (4FGL-DR4; The Fourth Fermi-LAT catalog Data Release 4, The Fermi-LAT collaboration 2023, arXiv:2307.12546). We searched for the existence of intermediate (days to years) timescale emission from a new gamma-ray transient source. Preliminary analysis indicates no significant (>5sigma) new excess emission (> 100 MeV) within the IC250813A 90% confidence localization. Assuming a power-law spectrum (photon index = 2.0 fixed) for a point source at the IC250813A best-fit position, the >100 MeV flux upper limit (95% confidence) is <9.3e-10 ph cm^-2 s^-1 for ~17-years (2008-08-04 / T0), <1.3e-08 (<2.2e-07) ph cm^-2 s^-1 for a 1-month (1-day) integration time before T0. Since Fermi normally operates in an all-sky scanning mode, regular monitoring of this source will continue. For this analysis, the Fermi-LAT contact person is L. Pfeiffer (leonard.pfeiffer at uni-wuerzburg.de). The Fermi LAT is a pair conversion telescope designed to cover the energy band from 20 MeV to greater than 300 GeV. It is the product of an international collaboration between NASA and DOE in the U.S. and many scientific institutions across France, Italy, Japan and Sweden. View this GCN Circular online at https://gcn.nasa.gov/circulars/41360. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39420] GRB 250813B: Swift-XRT afterglow detection
by GCN Circulars 14 Aug '25

14 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41359 SUBJECT: GRB 250813B: Swift-XRT afterglow detection DATE: 25/08/14 08:09:11 GMT FROM: K.L. Page at U Leicester <klp5(a)leicester.ac.uk> K.L. Page, A.P. Beardmore and P.A. Evans (U. Leicester) report on behalf of the Swift-XRT team: We have analysed 1.6 ks of XRT data for GRB 250813B, from 9.6 to 16.3 ks after the SVOM/ECLAIRs trigger (GCN Circ. 41354). The data are entirely in Photon Counting (PC) mode. We find an uncatalogued X-ray source at RA, Dec = 336.7505, +12.4613 which is equivalent to: RA (J2000): 22 27 00.13 Dec(J2000): +12 27 40.5 with an uncertainty of 3.7 arcsec (radius, 90% confidence). There is no evidence for fading during this interval, with the X-ray source showing a mean count rate of 0.17 +/- 0.02 count s^-1. However, the localisation of this source is consistent with the fading optical afterglow found by Ondrejov D50 (GCN Circ. 41353, 41355) and SVOM/COLIBRI (GCN Circ. 41356), and so we consider it the X-ray afterglow. A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.1 (+0.4, -0.3). The best-fitting absorption column is 2.5 (+1.3, -1.1) × 10^21 cm^-2, in excess of the Galactic value of 6.2 x 10^20 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 6.2 x 10^-12 (9.3 x 10^-12) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 2.5 (+1.3, -1.1) x 10^21 cm^-2 Galactic foreground: 6.2 x 10^20 cm^-2 Photon index: 2.1 (+0.4, -0.3) This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/41359. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39419] GRB 250813B: Swift-XRT afterglow detection
by GCN Circulars 14 Aug '25

14 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41359 SUBJECT: GRB 250813B: Swift-XRT afterglow detection DATE: 25/08/14 08:09:11 GMT FROM: K.L. Page at U Leicester <klp5(a)leicester.ac.uk> K.L. Page, A.P. Beardmore and P.A. Evans (U. Leicester) report on behalf of the Swift-XRT team: We have analysed 1.6 ks of XRT data for GRB 250813B, from 9.6 to 16.3 ks after the SVOM/ECLAIRs trigger (GCN Circ. 41354). The data are entirely in Photon Counting (PC) mode. We find an uncatalogued X-ray source at RA, Dec = 336.7505, +12.4613 which is equivalent to: RA (J2000): 22 27 00.13 Dec(J2000): +12 27 40.5 with an uncertainty of 3.7 arcsec (radius, 90% confidence). There is no evidence for fading during this interval, with the X-ray source showing a mean count rate of 0.17 +/- 0.02 count s^-1. However, the localisation of this source is consistent with the fading optical afterglow found by Ondrejov D50 (GCN Circ. 41353, 41355) and SVOM/COLIBRI (GCN Circ. 41356), and so we consider it the X-ray afterglow. A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.1 (+0.4, -0.3). The best-fitting absorption column is 2.5 (+1.3, -1.1) × 10^21 cm^-2, in excess of the Galactic value of 6.2 x 10^20 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 6.2 x 10^-12 (9.3 x 10^-12) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 2.5 (+1.3, -1.1) x 10^21 cm^-2 Galactic foreground: 6.2 x 10^20 cm^-2 Photon index: 2.1 (+0.4, -0.3) This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/41359. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39418] GRB 250814A: Swift detection of a burst coincident with a subthreshold GW trigger
by GCN Circulars 14 Aug '25

14 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41358 SUBJECT: GRB 250814A: Swift detection of a burst coincident with a subthreshold GW trigger DATE: 25/08/14 07:58:28 GMT FROM: K.L. Page at U Leicester <klp5(a)leicester.ac.uk> R. Caputo (GSFC), A. P. Beardmore (U Leicester), P. A. Evans (U Leicester), R. A. J. Eyles-Ferris (U Leicester), C. Gronwall (PSU), A. Y. Lien (U Tampa) and K. L. Page (U Leicester) report on behalf of the Neil Gehrels Swift Observatory Team: At 07:34:59 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 250814A (trigger=1342439). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 306.329, +48.391 which is RA(J2000) = 20h 25m 19s Dec(J2000) = +48d 23' 27" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a complex structure structure with a duration of about 20 sec. The peak at ~T+26 s in the 15-25 keV band raw light curve is likely due to detector noise, though further ground data is required to confirm this. The peak count rate was ~500 counts/sec (15-350 keV), at ~10 sec after the trigger. The XRT began observing the field at 07:37:54.1 UT, 174.3 seconds after the BAT trigger. Using promptly downlinked data we find a bright, fading, uncatalogued X-ray source with an enhanced position: RA, Dec 306.30802, 48.39903 which is equivalent to: RA(J2000) = 20h 25m 13.92s Dec(J2000) = +48d 23' 56.5" with an uncertainty of 2.2 arcseconds (radius, 90% containment). This location is 57 arcseconds from the BAT onboard position, within the BAT error circle. This position may be improved as more data are received; the latest position is available at https://www.swift.ac.uk/sper. A power-law fit to a spectrum formed from promptly downlinked event data gives a column density consistent with the Galactic value of 6.51 x 10^21 cm^-2 (Willingale et al. 2013). The initial flux in the 2.5 s image was 7.47e-10 erg cm^-2 s^-1 (0.2-10 keV). UVOT took a finding chart exposure of 250 seconds with the U filter starting 179 seconds after the BAT trigger. No credible afterglow candidate has been found in the initial data products. The 2.7'x2.7' sub-image covers 100% of the XRT error circle. The typical 3-sigma upper limit has been about 19.2 mag. The 8'x8' region for the list of sources generated on-board covers 100% of the XRT error circle. The list of sources is typically complete to about 18.0 mag. No correction has been made for the expected extinction corresponding to E(B-V) of 1.066. This GRB is temporally and spatially coincident with the subthreshold GW trigger S250814bg which occurred 6 s after the BAT trigger. The XRT position is towards the edge of the GW localisation. Given the low significance of the GW event (a false alarm rate of ~10/day) this is probably a chance coincidence; however, follow up of this GRB is advised. Burst Advocate for this burst is R. Caputo (regina.caputo AT nasa.gov) Please contact the BA by email if you require additional information regarding Swift followup of this burst. In extremely urgent cases, after trying the Burst Advocate, you can contact the Swift PI by phone (see Swift TOO web site for information: http://www.swift.psu.edu/) View this GCN Circular online at https://gcn.nasa.gov/circulars/41358. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39417] GRB 250814A: Fermi GBM Final Real-time Localization
by GCN Circulars 14 Aug '25

14 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41357 SUBJECT: GRB 250814A: Fermi GBM Final Real-time Localization DATE: 25/08/14 07:45:48 GMT FROM: Fermi GBM Team at MSFC/Fermi-GBM <do_not_reply(a)GIOC.nsstc.nasa.gov> The Fermi GBM team reports the detection of a likely LONG GRB At 07:35:09 UT on 14 Aug 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250814A (trigger 776849714.277078 / 250814316). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 298.0, Dec = 47.5 (J2000 degrees, equivalent to J2000 19h 52m, 47d 30'), with a statistical uncertainty of 8.6 degrees. The angle from the Fermi LAT boresight is 30.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250814316/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250814316/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250814316/… View this GCN Circular online at https://gcn.nasa.gov/circulars/41357. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39416] GRB 250813A: SVOM/COLIBRÍ (FM-GFT) optical observations
by GCN Circulars 14 Aug '25

14 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41356 SUBJECT: GRB 250813A: SVOM/COLIBRÍ (FM-GFT) optical observations DATE: 25/08/14 05:51:16 GMT FROM: Antonio de Ugarte Postigo at LAM, CNRS <adeugartepostigo(a)gmail.com> Ramandeep Gill (UNAM), Antonio de Ugarte Postigo (LAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Fredd Alvarez (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (OCA), Rosa L. Becerra (U Roma), Nathaniel R. Butler (ASU) , Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Benjamin Schneider (LAM), W.J. Xie (NAOC), and B.T. Wang (YNAO, CAS): We imaged the field of the SVOM GRB 250813A (W.J. Xie et al., GCN Circ. 41352) using the DDRAGO wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope. We observed from 2025-08-14 04:05:30 to 04:44:19 UTC (mean epoch 5.5618 hours after the trigger) and obtained 32x60 s of exposure in the i filter. The data were reduced and coadded with the COLIBRÍ pipeline and analyzed with STDWeb/STDPipe (Karpov 2025). The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction. We detected the optical counterpart reported by Jelinek et al., GCN Circs. 41353 and 41355, at a preliminary magnitude of: i = 21.38 +/- 0.09 Further observations are ongoing. We thank the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir and the COLIBRÍ and DDRAGO engineering teams. COLIBRÍ is an astronomical observatory developed and operated jointly by France (AMU, CNES and CNRS) and Mexico (UNAM and SECIHTI). It is located at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, Mexico. View this GCN Circular online at https://gcn.nasa.gov/circulars/41356. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39415] GRB 250813B: Ondrejov D50 fast decay
by GCN Circulars 14 Aug '25

14 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41355 SUBJECT: GRB 250813B: Ondrejov D50 fast decay DATE: 25/08/14 00:46:58 GMT FROM: Martin Jelinek at Astro.Inst-AVCR,Ondrejov <martin.jelinek(a)asu.cas.cz> M. Jelinek, J. Strobl, F. Novotny, R. Hudec (ASU CAS Ondrejov) report: Further to our earlier report (GCN 41353), we provide refined photometric analysis of the optical afterglow of GRB 250813B (Xie et al., GCN 41352). Our photometry reveals an extremely rapid decay with the afterglow fading from the initial magnitude of ~14.4 at ~100s post-trigger to near magnitude 20 at 0.03 days (43 minutes) after the trigger. This represents a fade of approximately 5.6 magnitudes in less than one hour and an average decay rate of ~1.8. Potential observers should note the rapid evolution when planning follow-up observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/41355. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39414] GRB 250813B: SVOM detection of a bright long burst (Correction for GCN 41352).
by GCN Circulars 14 Aug '25

14 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41354 SUBJECT: GRB 250813B: SVOM detection of a bright long burst (Correction for GCN 41352). DATE: 25/08/14 00:40:48 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> W.J. XIE (NAOC), B.T. WANG (YNAO, CAS), O. Godet, H. Yang (IRAP), H. Goto (CEA, Kanazawa univ.), F. Robinet (IJCLAB), L. Zhang (IHEP) This GCN circular is the correction version for the GCN 41352. We sorry for the mistake in the GCN 41352, where the GRB name shall be GRB 250813B but not GRB 250813A. At 2025-08-13T22:51:12 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 250813B (SVOM burst-id sb25081303). The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network. The burst was detected both by the Count-Rate Trigger (CRT) and the Image Trigger (IMT), which produced a sequence of 16 alerts. CRT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 92.23 in the [8-120] keV energy band over a time window of 20.4 seconds starting at 2025-08-13T22:51:15. The localization of the best alert is R.A., Dec. 336.728, 12.498 degrees (J2000) with a 90% confidence level (C.L.) radius of 2.17 arcmin (including systematic error of 2 arcmin added in quadrature). This burst also triggered SVOM/GRM at 2025-08-13T22:51:11 on a timescale of 1 second with an SNR of 8. SVOM slewed to the burst. SVOM/MXT began observing the field at 2025-08-13T22:54:00 UTC, 168 seconds after T0. Using onboard processed data we found an uncatalogued X-ray source located at R.A., Dec. 336.7591, 12.4479 degrees: R.A. (J2000) = 22h27m02.19s Dec. (J2000) = 12d26m52.70s with a 90% C.L. radius of 71 arcseconds including systematics. This location is 3.51 arcminutes from the ECLAIRs onboard position. This position may be improved as more data is received. VT began observing the field after the slew. The analysis of the data will be published in a future circular. The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. SVOM/ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC. SVOM/GRM was developed by the Institute of High Energy Physics (IHEP) of CAS. SVOM/MXT was developed jointly by CNES, CEA-IRFU, CNRS-IJCLab, University of Leicester, MPE. The Burst Advocate (BA) on shift for this alert is Wenjin XIE (xiewj(a)bao.ac.cn) Please contact the BA by email if you require additional information. View this GCN Circular online at https://gcn.nasa.gov/circulars/41354. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39413] GRB 250813B: Ondrejov D50 optical afterglow detection
by GCN Circulars 14 Aug '25

14 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41353 SUBJECT: GRB 250813B: Ondrejov D50 optical afterglow detection DATE: 25/08/14 00:09:05 GMT FROM: Martin Jelinek at Astro.Inst-AVCR,Ondrejov <martin.jelinek(a)asu.cas.cz> M. Jelinek, J. Strobl, F. Novotny, R. Hudec (ASU CAS Ondrejov)report:We observed the position of the SVOM-detected GRB 250813B (Xie et al., GCN 41352) with the D50 robotic telescope of the Astronomical Institute Ondrejov, near Prague, Czech Republic. We performed a series of 10s unfiltered exposuresstarting at 22:52:44.496 UT, i.e. 93.5s after the trigger.We detect the optical afterglow at 22:27:00.15 +12:27:44.5 (J2000), consistent with both the ECLAIRs localization (Xie et al., GCN 41352) and the refined MXTX-ray position. The source is clearly detected in single 10s unfiltered images. View this GCN Circular online at https://gcn.nasa.gov/circulars/41353. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39412] GRB 250813A: SVOM detection of a bright long burst
by GCN Circulars 13 Aug '25

13 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41352 SUBJECT: GRB 250813A: SVOM detection of a bright long burst DATE: 25/08/13 23:38:17 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> W.J. XIE (NAOC), B.T. WANG (YNAO, CAS), O. Godet, H. Yang (IRAP), H. Goto (CEA, Kanazawa univ.), F. Robinet (IJCLAB), L. Zhang (IHEP) At 2025-08-13T22:51:12 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 250813A (SVOM burst-id sb25081303). The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network. The burst was detected both by the Count-Rate Trigger (CRT) and the Image Trigger (IMT), which produced a sequence of 16 alerts. CRT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 92.23 in the [8-120] keV energy band over a time window of 20.4 seconds starting at 2025-08-13T22:51:15. The localization of the best alert is R.A., Dec. 336.728, 12.498 degrees (J2000) with a 90% confidence level (C.L.) radius of 2.17 arcmin (including systematic error of 2 arcmin added in quadrature). This burst also triggered SVOM/GRM at 2025-08-13T22:51:11 on a timescale of 1 second with an SNR of 8. The lightcurve of GRM could be found below. https://www.bursthub.cn//admin/static/svgrb250813A.png SVOM slewed to the burst. SVOM/MXT began observing the field at 2025-08-13T22:54:00 UTC, 168 seconds after T0. Using onboard processed data we found an uncatalogued X-ray source located at R.A., Dec. 336.7591, 12.4479 degrees: R.A. (J2000) = 22h27m02.19s Dec. (J2000) = 12d26m52.70s with a 90% C.L. radius of 71 arcseconds including systematics. This location is 3.51 arcminutes from the ECLAIRs onboard position. This position may be improved as more data is received. VT began observing the field after the slew. The analysis of the data will be published in a future circular. The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. SVOM/ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC. SVOM/GRM was developed by the Institute of High Energy Physics (IHEP) of CAS. SVOM/MXT was developed jointly by CNES, CEA-IRFU, CNRS-IJCLab, University of Leicester, MPE. The Burst Advocate (BA) on shift for this alert is Wenjin XIE (xiewj(a)bao.ac.cn) Please contact the BA by email if you require additional information. View this GCN Circular online at https://gcn.nasa.gov/circulars/41352. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39411] LIGO/Virgo/KAGRA S250813k: NED Galaxies in the 4-Update Localization Volume
by GCN Circulars 13 Aug '25

13 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41351 SUBJECT: LIGO/Virgo/KAGRA S250813k: NED Galaxies in the 4-Update Localization Volume DATE: 25/08/13 22:45:01 GMT FROM: David Cook at Caltech/IPAC-NED <dcook(a)ipac.caltech.edu> David O. Cook (Caltech/IPAC), Rick Ebert (Caltech/IPAC), George Helou (Caltech/IPAC), Joseph M. Mazzarella (Caltech/IPAC), Marion Schmitz (Caltech/IPAC), and Leo Singer (NASA/GSFC) On behalf of the NASA/IPAC Extragalactic Database (NED) Team. We spatially cross-matched the LVK S250813k-4-Update sky localization with the NED Local Volume Sample (NED-LVS; Cook et al. 2023), which is a subset of NED with a redshift or redshift-independent distance less than 1000 Mpc. We find 155 galaxies within the 90% containment volume, and we list here the top 20 galaxies sorted by the joint probability of the 3D localization and the WISE W1 luminosity (an observable proxy for stellar mass). For the full or top 20 list of galaxies in the 90% volume go either to the NED Gravitational Wave Followup service at https://ned.ipac.caltech.edu/uri/NED::GWF/ or click on the following links: Full List Download: https://ned.ipac.caltech.edu/uri/NED::GWFglist/fits/S250813k/4 Top 20 List Download: https://ned.ipac.caltech.edu/uri/NED::GWFglist/fits/S250813k/4/20 The NED-GWF service provides downloadable galaxy lists and visualizations for candidate host galaxies. For each GW alert, these products are automatically generated and made available within minutes to expedite efficient electromagnetic follow-up observations. The NED top 20 list is sorted by the joint probability of the 3D localization and the WISE W1 luminosity, but users can sort on additional pre-computed prioritization metrics (star formation rate, P_3D * P_SFR; and specific star formation rate, P_3D * P_sSFR; etc.) which are available via downloading the entire galaxy list inside the event's probability volume. | objname| ra| dec|objtype| DistMpc|DistMpc_unc| m_NUV| m_NUV_unc| m_Ks| m_Ks_unc| m_W1| m_W1_unc| P_3D|P_3D_LumW1| |-------------------------|--------------|--------------|-------|-----------|-----------|------------|------------|------------|------------|------------|------------|--------|----------| |WISEA J091600.60+754837.0| 139.00362| 75.80978| G| 743.12| null| null| null| 12.790| 0.114| 11.225| 0.006|1.02e-06| 6.45e-08| |WISEA J085943.95+740702.1| 134.93483| 74.11685| G| 744.63| null| null| null| 13.083| 0.113| 12.827| 0.010|3.05e-06| 4.44e-08| |WISEA J090329.43+731952.8| 135.87263| 73.33136| G| 769.02| null| null| null| 13.434| 0.144| 12.868| 0.010|2.18e-06| 3.25e-08| |WISEA J090156.31+745448.6| 135.48465| 74.91352| G| 608.62| null| null| null| 13.563| 0.165| 13.395| 0.025|5.01e-06| 2.88e-08| |WISEA J090057.52+734556.4| 135.23969| 73.76568| G| 531.03| null| null| null| 12.743| 0.128| 12.700| 0.011|3.30e-06| 2.75e-08| |WISEA J085751.67+730314.9| 134.46530| 73.05415| G| 560.91| null| 20.368| 0.159| 13.715| 0.146| 12.494| 0.013|2.36e-06| 2.65e-08| |WISEA J091306.11+753712.2| 138.27548| 75.62007| G| 501.03| null| null| null| 12.896| 0.123| 12.393| 0.009|2.67e-06| 2.62e-08| |WISEA J085557.92+730643.9| 133.99135| 73.11222| G| 729.14| null| null| null| 13.591| 0.164| 13.317| 0.012|2.84e-06| 2.53e-08| |WISEA J090309.87+740351.7| 135.79113| 74.06438| G| 690.65| null| null| null| 13.836| 0.169| 13.566| 0.025|4.00e-06| 2.53e-08| |WISEA J090722.74+745314.9| 136.84477| 74.88750| G| 560.31| null| null| null| 13.366| 0.150| 13.349| 0.025|4.85e-06| 2.47e-08| |WISEA J090920.49+732006.8| 137.33539| 73.33525| G| 649.99| null| null| null| 13.738| 0.164| 12.081| 0.010|1.11e-06| 2.44e-08| |WISEA J085409.21+730852.6| 133.53838| 73.14795| G| 890.70| null| null| null| 13.089| 0.117| 12.653| 0.012|9.25e-07| 2.28e-08| |WISEA J090616.44+751235.5| 136.56851| 75.20987| G| 653.18| null| null| null| 13.689| 0.176| 13.670| 0.028|4.42e-06| 2.27e-08| |WISEA J090229.38+732949.1| 135.62244| 73.49698| G| 623.66| null| 20.646| 0.194| 13.692| 0.161| 13.281| 0.013|3.29e-06| 2.21e-08| |WISEA J090910.90+751628.1| 137.29543| 75.27447| G| 637.20| null| null| null| 13.552| 0.144| 13.679| 0.022|4.28e-06| 2.08e-08| |WISEA J090759.32+734442.1| 136.99718| 73.74504| G| 667.18| null| null| null| 13.483| 0.149| 13.309| 0.013|2.68e-06| 2.01e-08| |WISEA J091645.14+761451.5| 139.18812| 76.24766| G| 579.30| null| null| null| 13.414| 0.194| 13.098| 0.015|2.81e-06| 1.93e-08| |WISEA J085617.59+731958.6| 134.07330| 73.33295| G| 601.79| null| null| null| 13.364| 0.135| 13.299| 0.012|2.78e-06| 1.71e-08| |WISEA J090653.45+762059.4| 136.72274| 76.34984| G| 699.37| null| null| null| 13.345| 0.179| 12.327| 0.010|8.26e-07| 1.68e-08| |WISEA J085525.06+732139.9| 133.85446| 73.36109| G| 552.18| null| null| null| 13.243| 0.122| 12.856| 0.014|2.06e-06| 1.61e-08| Table 1: Top 20 galaxies in NED-LVS that fall in the 90% probability volume for S250813k sorted by the joint probability of 3D position and WISE W1 luminosity (P_3D * P_LumW1). Galaxy is the NED preferred name. RA and Dec are the Equatorial coordinates in degrees (J2000). Objtype is the object type of the galaxy candidate. Distance is the distance to the galaxy in Mpc. m_NUV and mErr_NUV are the apparent magnitude and error from GALEX. m_Ks and mErr_Ks are the apparent magnitude and error from 2MASS. m_W1 and mErr_W1 are the apparent magnitude and error from AllWISE. P_3D is the probability that the galaxy is in the volume given the distance of GW event. P_3D_LumW1 is the joint probability within the volume weighted by the WISE1 luminosity of the galaxy (P_3D * P_LumW1). View this GCN Circular online at https://gcn.nasa.gov/circulars/41351. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39410] LIGO/Virgo/KAGRA S250813k: Updated Sky localization
by GCN Circulars 13 Aug '25

13 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41350 SUBJECT: LIGO/Virgo/KAGRA S250813k: Updated Sky localization DATE: 25/08/13 21:55:57 GMT FROM: Sylvia Biscoveanu at Northwestern CIERA <sylvia.biscoveanu(a)ligo.org> The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report: We have conducted further analysis of the LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) data around the time of the compact binary merger (CBC) candidate S250813k (GCN Circular 41336). Parameter estimation has been performed using Bilby [1] and a new sky map, Bilby.multiorder.fits,0, distributed via GCN and SCiMMA notices, is available for retrieval from the GraceDB event page: https://gracedb.ligo.org/superevents/S250813k For the Bilby.multiorder.fits,0 sky map, the 90% credible region is well fit by an ellipse with an area of 13 deg2 described by the following DS9 region (right ascension, declination, semi-major axis, semi-minor axis, position angle of the semi-minor axis): icrs; ellipse(09h02m, +74d05m, 3.72d, 1.09d, 106.41d) Marginalized over the whole sky, the a posteriori luminosity distance estimate is 708 +/- 159 Mpc (a posteriori mean +/- standard deviation). For further information about analysis methodology and the contents of this alert, refer to the LIGO/Virgo/KAGRA Public Alerts User Guide https://emfollow.docs.ligo.org/. [1] Ashton et al. ApJS 241, 27 (2019) doi:10.3847/1538-4365/ab06fc and Morisaki et al. PRD 108, 123040 (2023) doi:10.1103/PhysRevD.108.123040 View this GCN Circular online at https://gcn.nasa.gov/circulars/41350. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39409] EP250812a: Nickel optical upper limit
by GCN Circulars 13 Aug '25

13 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41349 SUBJECT: EP250812a: Nickel optical upper limit DATE: 25/08/13 18:18:02 GMT FROM: Weikang Zheng at UC Berkeley <weikang(a)berkeley.edu> Andreas Betz, Riley Patlak, WeiKang Zheng and Alex Filippenko (UC Berkeley) report on behalf of the KAIT GRB team: We observed the field of EP250812a (Zhang et al., GCN 41327) with the 1-m Nickel telescope located at Lick observatory, California. Observations were performed in the R band with 600s x 5 exposures. In our coadd image, we do not detect the optical counterpart (Xin et al., GCN 41340; Ducoin et al., GCN 41342) with an upper limit of R > 20.7 (Vega) at a mid-time of 23.8 hours after the trigger. View this GCN Circular online at https://gcn.nasa.gov/circulars/41349. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39408] GRB 250812A: VLT X-shooter spectroscopic redshift confirmation z = 2.571
by GCN Circulars 13 Aug '25

13 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41348 SUBJECT: GRB 250812A: VLT X-shooter spectroscopic redshift confirmation z = 2.571 DATE: 25/08/13 18:02:09 GMT FROM: Gregory Corcoran at University College Dublin <gregory.corcoran(a)ucdconnect.ie> A. de Ugarte Postigo (LAM), B. Schneider (LAM), G. Corcoran (UCD), D. B. Malesani (DAWN/NBI and Radboud), J. An (NAOC), E. Le Floc’h (CEA), A. Martin-Carrillo (UCD), M. De Pasquale (Univ. of Messina) report on behalf of the Stargate collaboration: We observed the optical afterglow (He et al., GCN 41324; Xin et al., GCN 41326; Rakotondrainibe et al., GCN 41328; Freeberg et al., GCN 41331; Siegel et al., GCN 41344; Santos et al., GCN 41346; van Dalen et al., GCN 41347) of GRB 250812A detected by SVOM/ECLAIRs (Xin et al., GCN 41322) with ESO VLT UT3 (Melipal) equipped with the X-shooter spectrograph. In a 30 s image taken with the acquisition camera on Aug 13 at 09:25 UT (30.65 hr after the ECLAIRs trigger), the optical afterglow is clearly detected for which we measure a preliminary magnitude r = 19.5 +/- 0.2 AB (calibrated against 1 star from SkyMapper catalog). Our spectra cover the wavelength range 3000-21000 AA, and consist of 2 exposures of 600 s each. Observations started on 2025-08-13 at approximately 09:26 UT (30.7 hr after the SVOM trigger). In a preliminary reduction of the spectra, we detect a continuum over the entire covered wavelength range. From the detection of a broad trough as well as numerous narrow absorption lines, which we interpret as due to Lya, NV, Si II, Si II*, O I, C II, C II*, Si IV, Si II, C IV, Al II, Al III, Fe II, and Mg II, we infer a redshift of z = 2.571, that we securely identify as the redshift of GRB 250812A confirming, and refining, the result from van Dalen et al. (GCN 41347). We acknowledge excellent support from the ESO observing staff in Paranal, in particular Akke Corporaal, Rob van Holstein and Rodrigo Romero. The analysis of this spectrum was carried out with the help of the zHunter tool (https://doi.org/10.5281/zenodo.15189495) View this GCN Circular online at https://gcn.nasa.gov/circulars/41348. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39407] GRB 250812A: NTT spectroscopic redshift z = 2.57
by GCN Circulars 13 Aug '25

13 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41347 SUBJECT: GRB 250812A: NTT spectroscopic redshift z = 2.57 DATE: 25/08/13 17:10:45 GMT FROM: Antonio Martin-Carrillo at UCD,Space Science Group <antonio.martin-carrillo(a)ucd.ie> J. N. D. van Dalen (Radboud), D. B. Malesani (DAWN/NBI and Radboud), G. Corcoran (UCD), L. Cotter (UCD), M. Fraser (UCD), A. Martin-Carrillo (UCD), A. Aryan (NCU), M. Dennefeld (IAP), G. Pignata (IAI), P. D'Avanzo (INAF/OAB), A. de Ugarte Postigo (LAM), J. Anderson (ESO), T. Müller Bravo (Southampton), T.-W. Chen (NCU), M. Gromadzki (Warsaw), C. Inserra (Cardiff), E. Kankare (Turku), M. Nicholl (QUB), O. Yaron (Weizmann), D. Young (QUB), E. Zimmerman (Weizmann) report on behalf of the ePESSTO+ collaboration: We observed the optical counterpart of the SVOM/ECLAIRs GRB 250812A (Xin et al., GCN 41322) using the ESO New Technology Telescope (NTT) located in La Silla (Chile), equipped with the EFOSC2 camera. A total of 360 s imaging was secured in Gunn r starting at 2025-08-13 04:28:26 (1.074 days after the trigger). The optical afterglow reported by He et al. (GCN 41324), Xin et al. (GCN 41326), Rakotondrainibe et al. (GCN 41328), Freeberg et al. (GCN 41331), Siegel et al. (GCN 41344), and Santos et al. (GCN 41346) is well detected in our images with a magnitude r = 19.7 +/- 0.1 AB (calibrated against nearby stars from the Legacy Sky Survey catalog) and not corrected for Galactic extinction. A 3000 s spectroscopic observation was subsequently obtained starting at 2025-08-13 06:30:20 (1.16 days after the trigger), again using EFOSC2 equipped with grism 13. In a preliminary reduction of the spectrum, the source is well detected across the full spectral range from 3985 to 9315 AA. While the S/N is too low to confidently identify individual metal absorption features, a strong absorption trough is clearly visible at ~4344 AA, which we interpret as a DLA. From this DLA feature we infer a redshift of 2.57 which we suggest to be the redshift of GRB 250812A. We acknowledge expert support from the NTT operator, Pablo Arias. View this GCN Circular online at https://gcn.nasa.gov/circulars/41347. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39406] GRB250812a: STEP/T80S Indication of slow decay of afterglow
by GCN Circulars 13 Aug '25

13 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41346 SUBJECT: GRB250812a: STEP/T80S Indication of slow decay of afterglow DATE: 25/08/13 15:31:30 GMT FROM: André Santos at Centro Brasileiro de Pesquisas Físicas (CBPF) <andsouzasanttos(a)gmail.com> A. Santos (CBPF), C. R. Bom (CBPF), C. D. Kilpatrick (Northwestern), L. Santana-Silva (CBPF), P. Darc (CBPF), Gabriel Teixeira (CBPF), C. Mendes de Oliveira (IAG-USP) report on behalf of the STEP collaboration: We conducted optical follow up with the T80S 0.8-m robotic telescope as part of the S-PLUS Transient Extension Program (Santos et al., 2024, MNRAS, 529, 59) targeting the faint, long gamma-ray burst GRB250812A discovered by the SVOM/ECLAIRs instrument (GCN 41322). The T80S observations started on Aug 13 08:36:48 UT (~30 hours after the trigger). We obtained images totaling 600s (2x300s) in r-band and in i-band with the T80S camera centered at the position of the optical afterglow detection reported in He et al. (GCN 41324), Xin et al. (GCN 41326), Rakotondrainibe et al. (GCN 41328) and Freeberg et al. (GCN 41331). Subtracting DECam template images from the T80S individual frames using photpipe (Rest et al., 2005, ApJ, 634, 1103), we detect the afterglow at the previously reported position. MJD Filter Magnitude Uncertainty 60900.358890 r 19.816 0.127 60900.362940 r 19.925 0.111 60900.366880 i 19.438 0.087 60900.370920 i 19.589 0.094 The reported magnitudes in r and i-bands 30 hours post burst in template-subtracted images indicate a slow decay for the afterglow. We encourage further follow-up observations to better characterize the transient and the source of its optical emission. We acknowledge the T80S technical team with the provided support during the night. View this GCN Circular online at https://gcn.nasa.gov/circulars/41346. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39405] EP250812a: NOT, NTT, and GS observations
by GCN Circulars 13 Aug '25

13 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41345 SUBJECT: EP250812a: NOT, NTT, and GS observations DATE: 25/08/13 15:23:05 GMT FROM: Jonathan Quirola at Radboud University <jaquirola1990(a)gmail.com> A. P. C. van Hoof (Radboud), J. A. Quirola-Vasquez (Radboud), J. N. D. van Dalen (Radboud), D. B. Malesani (DAWN/NBI and Radboud), L. Cotter (UCD), M. Fraser (UCD), G. Corcoran (UCD), P. G. Jonker (Radboud), A. Martin-Carrillo (UCD), A. J. Levan (Radboud and Warwick), F. E. Bauer (SSI and UTA), report on behalf of a larger collaboration: We observed the field of the fast X-ray transient EP250812a (Zhang et al., GCN 41327, GCN 41339) using the Nordic Optical Telescope (NOT, equipped with the ALFOSC camera), the New Technology Telescope (NTT, with the EFOSC2 instrument), and the Gemini South Telescope (GS, with the FLAMINGOS2, F2, instrument). Observations with NTT were also carried out in the r filter (3x600 s) starting on 2025-08-13 05:22:07.8 UT, i.e., ~16.2 hr after the trigger. Moreover, NOT and NTT observations were carried out in the z filters (15x80 s and 6x300 s) starting on 2025-08-13 05:31:57.8 and 2025-08-13 05:40:17.2 UT, i.e, ~16.4 and 16.5 hr after the X-ray trigger, respectively. The GS-F2 visited the field using the H filter (20x10 s) starting on 2025-08-13 07:35:11.0 UT, i.e.,~18.4 hr after the trigger. At the location of the transient reported by Zhang et al. (GCN 41327) and the optical counterpart from SVOM/VT reported by Xin et al. (GCN 41340) and from COLIBRI (Ducoin et al., GCN 41342), also consistent with the EP/FXT (Zhang et al., GCN 41339) and Swift/XRT positions (Evans et al., GCN 41330), no source is detected, down to 3-sigma limiting magnitudes: H > 22.0 (GS) z > 22.5 (NOT) z > 22.3 (NTT) r > 22.6 (NTT) These upper limits are in AB magnitudes and were calibrated using nearby stars from the Pan-STARRS and 2MASS catalogues and not corrected by galactic extinction. We thank the excellent support from the observing staff at Gemini (especially Cinthya Rodrigez), NOT (in particular Emil Knudstrup), and NTT (in particular Pablo Arias). View this GCN Circular online at https://gcn.nasa.gov/circulars/41345. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39404] GRB 250812A: Swift/UVOT Detection
by GCN Circulars 13 Aug '25

13 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41344 SUBJECT: GRB 250812A: Swift/UVOT Detection DATE: 25/08/13 15:15:44 GMT FROM: Mike Siegel at PSU/Swift MOC <mhs18(a)psu.edu> M. H. Siegel (PSU) reports on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 250812A 6.5 ks after the SVOM/ECLAIRs trigger (Xin et al., GCN Circ. 41322). An uncatalogued source consistent with the XRT position (Sbarrato et al., GCN Circ. 41325) and the optical transient (He et al., GCN Circ. 41324; Xin et al., GCN Circ. 41326; Rakotondrainibe et al., GCN Circ. 41328; Freeberg et al., GCN Circ. 41333) is detected in the UVOT exposures. However, we note that the source shows no evidence of fading in the 67 ks between the two Swift epochs. The preliminary UVOT position is: RA (J2000) = 02:11:13.68 = 32.80701 (deg.) Dec (J2000) = -43:09:49.1 = -43.16363 (deg.) with an estimated uncertainty of 0.42 arc sec. (radius, 90% confidence). Preliminary detections and 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag u 6500 12380 1479 19.43+/-0.12 u 73801 90784 695 19.48+/-0.13 v 74444 91365 424 >19.24 white 74122 91182 695 19.96+/-0.10 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.012 in the direction of the burst (Schlegel et al. 1998). View this GCN Circular online at https://gcn.nasa.gov/circulars/41344. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39403] GRB 250813A: Fermi GBM Final Localization
by GCN Circulars 13 Aug '25

13 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41343 SUBJECT: GRB 250813A: Fermi GBM Final Localization DATE: 25/08/13 13:54:08 GMT FROM: eliza.neights(a)gmail.com The Fermi GBM team reports the detection of a likely LONG GRB "At 01:46:03.86 UT on 13 August 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250813A (trigger 776742368/250813074). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 355.90, Dec = 57.28 (J2000 degrees, equivalent to J2000 23h 43m, +57d 16'), with a statistical uncertainty of 3.06 degrees. The angle from the Fermi LAT boresight is 19 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250813074/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250813074/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250813074/…" View this GCN Circular online at https://gcn.nasa.gov/circulars/41343. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39402] EP250813a: COLIBRÍ detection of the VT candidate and evidence of flattening
by GCN Circulars 13 Aug '25

13 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41342 SUBJECT: EP250813a: COLIBRÍ detection of the VT candidate and evidence of flattening DATE: 25/08/13 13:44:03 GMT FROM: Rosa L. Becerra at Tor Vergata, Roma <rosa.becerra(a)roma2.infn.it> Jean-Grégoire Ducoin (CPPM), Camila Angulo (UNAM), Rosa L. Becerra (U Roma), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Fredd Alvarez (UNAM), Jean-Luc Atteia (IRAP), Dalya Akl (NYUAD), Sarah Antier (OCA), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM): We imaged the field of the EP250812a (Zhang et al., GCN Circ. 41327, 41339) using the DDRAGO wide-field imager on the COLIBRÍ telescope. We observed from 2025-08-13 08:00 to 10:21 UTC (from 18.8 to 21.2 hours after the trigger) and obtained 96 minutes of exposure in the i filter. The data were reduced and coadded with the COLIBRÍ pipeline and analysed with STDWeb/STDPipe (Karpov 2025). The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction. In the stacked image, we marginally detect the VT candidate (Xin et al., GCN Circ. 41330), which is also consistent with the XRT Source 1 position (Evans et al., GCN Circ. 41340), at: i = 22.5 +/- 0.3 This value is similar to the second observation reported by VT (Xin et al., GCN Circ. 41330) at T + 14.34 h, but brighter than in the Legacy Survey DR10 catalog (Dey et al. 2019): i = 23.5 +/- 0.1 Therefore, we suggest that the candidate is indeed the afterglow of EP250812a and that it showed evidence of a flattening in its evolution at the time of our observations. Further observations and analysis are ongoing. We thank the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir and the COLIBRÍ and DDRAGO engineering teams. COLIBRÍ is an astronomical observatory developed and operated jointly by France (AMU, CNES and CNRS) and Mexico (UNAM and SECIHTI). It is located at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, Mexico. View this GCN Circular online at https://gcn.nasa.gov/circulars/41342. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39401] EP250812a: Liverpool Telescope upper limits
by GCN Circulars 13 Aug '25

13 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41341 SUBJECT: EP250812a: Liverpool Telescope upper limits DATE: 25/08/13 10:28:50 GMT FROM: A. Bochenek at Liverpool John Moores University <a.m.bochenek(a)2023.ljmu.ac.uk> A. Bochenek and D. A. Perley (LJMU) report: We observed the field of the fast X-ray transient EP250812a (Zhang et al., GCN 41327) using the IO:O optical camera on the 2m robotic Liverpool Telescope. We obtained 8x100s exposures in the SDSS r’ and z’ filters starting at 2025-08-13 03:13:06 UT, approximately 14 hours after the trigger. We do not detect any new objects within the EP/FXT error region of the transient (Zhang et al., GCN 41327; Zhang et al., GCN 41339). The 3-sigma limiting magnitudes on the stacked images are r > 21.71 mag and z > 21.53 mag. This is in agreement with the detection of an optical counterpart candidate by SVOM/VT at VT_R = 22.74 ± 0.15 at 14.3 hours (Xin et al., GCN 41340). View this GCN Circular online at https://gcn.nasa.gov/circulars/41341. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39400] EP250812a: SVOM/VT optical counterpart
by GCN Circulars 13 Aug '25

13 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41340 SUBJECT: EP250812a: SVOM/VT optical counterpart DATE: 25/08/13 09:40:18 GMT FROM: Liping Xin at NAOC, SVOM <xlp(a)nao.cas.cn> L. P. Xin, H. L. Li, Y. N. Ma, Y. L. Qiu, C. Wu, Z. H. Yao, Y. Xu, J. Wang, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA) report on behalf of the SVOM/VT team. SVOM performed two Target of Opportunity observations of EP250812a detected by EP/WXT (Zhang et al., GCN 41327). The first epoch is from 2025-08-12T20:32:53 UTC, 7.38 hours after the EP trigger time. The second epoch is from 2025-08-13T01:47:59, 12.64 hours post the trigger. No any uncatalogued sources, compared to Lagecy survey, was found using VT X-band data, within the errorbox of EP/FXT (Zhang et al., GCN 41327, GCN 41339) or Swift/XRT (Evans et al., GCN 41330). However, there is a cataloged source in Legacy survey within the errorbox of Swift/XRT source1 with a distance of 3.4 arcseconds at R.A.=30.993037 Dec=-9.318883 degrees: RA (J2000) = 02:03:58.329 Dec (J2000) = -09:19:07.98 with an uncertainty of 0.5 arcsec. The cataloged source was detected in both VT_B and VT_R images. The magnitudes are derived as below: DeltaT(Mid time) | exposure time (s) | band | mag (AB) | mag err ---------------------- |-------------------|------|----------|-------- 7.62 hours | 26*70 | VT_B | 22.52 | 0.15 7.62 hours | 26*70 | VT_R | 22.04 | 0.12 14.34 hours | 75*70 | VT_B | 23.10 | 0.16 14.34 hours | 67*70 | VT_R | 22.74 | 0.15 Our photometry is not corrected for Galactic extinction. Given the fading of the source in our observations, we proposed that it is the counterpart of the transient. The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS. View this GCN Circular online at https://gcn.nasa.gov/circulars/41340. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39399] EP250812a: refined analysis of the EP-WXT and EP-FXT observations
by GCN Circulars 13 Aug '25

13 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41339 SUBJECT: EP250812a: refined analysis of the EP-WXT and EP-FXT observations DATE: 25/08/13 08:57:14 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> M.H. Zhang (NAO, CAS), H. Zhou (PMO, CAS), W. D. Zhang (NAO, CAS) report on behalf of the Einstein Probe team: The X-ray transient EP250812a was detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Zhang et al., GCN 41327). Refined analysis of the WXT data shows that the event started at T0=2025-08-12 13:10:18 (UTC) and lasted for about 37 s before the interruption of the autonomous follow-up. The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a Galactic hydrogen column density of 2.5 x 10^20 cm^-2 and a photon index of 1.0 (-0.3/+0.3). The derived average unabsorbed 0.5-4 keV flux is 6.7(-0.8/+0.8) x 10^(-10) erg/s/cm^2. The Follow-up X-ray Telescope (FXT) on board EP observed this source autonomously about 111 s after T0. On-ground analysis of the FXT data found an uncatalogued source at R.A. = 30.9931, DEC = -9.3191 (J2000) with an uncertainty of about 10 arcsec (radius, 90% C.L. statistical and systematic), which is consistent positionally with the WXT transient. The average 0.5-10 keV spectrum can be fitted with an absorbed power law with a Galactic hydrogen column density of 2.5 x 10^20 cm^-2 and a photon index of 2.21 (-0.18/+0.20). The absorption from the host galaxy cannot be constrained. The derived average unabsorbed 0.5-10 keV flux is 1.97 (-0.13/+0.21) x 10^(-12) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). View this GCN Circular online at https://gcn.nasa.gov/circulars/41339. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39398] IceCube-250813A - IceCube observation of a high-energy neutrino candidate track-like event
by GCN Circulars 13 Aug '25

13 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41338 SUBJECT: IceCube-250813A - IceCube observation of a high-energy neutrino candidate track-like event DATE: 25/08/13 08:05:29 GMT FROM: A. Zegarelli at Ruhr University Bochum <azegarelli(a)icecube.wisc.edu> The IceCube Collaboration (http://icecube.wisc.edu/) reports: On 2025-08-13 03:21:09.69 UT IceCube detected a track-like event with a moderate probability of being of astrophysical origin. The event was selected by the ICECUBE_Astrotrack_Bronze alert stream. The average astrophysical neutrino purity for Bronze alerts is 30%. This alert has an estimated false alarm rate of 2.0759 events per year due to atmospheric backgrounds. The IceCube detector was in a normal operating state at the time of detection. After the initial automated alert (https://gcn.gsfc.nasa.gov/notices_amon_g_b/141240_9390028.amon) more sophisticated reconstruction algorithms have been applied offline, with the direction refined to: Date: 2025-08-13 Time: 03:21:09.69 UT RA: 275.36 (+0.84, -0.94 deg 90% PSF containment) J2000 Dec: 8.27 (+0.79, -0.75 deg 90% PSF containment) J2000 We encourage follow-up by ground and space-based instruments to help identify a possible astrophysical source for the candidate neutrino. No known gamma-ray sources listed in the Fermi 4FGL-DR4 or 3FHL catalogs are located within the 90% uncertainty region of the event. The IceCube Neutrino Observatory is a cubic-kilometer neutrino detector operating at the geographic South Pole, Antarctica. The IceCube realtime alert point of contact can be reached at roc(a)icecube.wisc.edu View this GCN Circular online at https://gcn.nasa.gov/circulars/41338. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39397] IceCube Alert 250813.14: Global MASTER-Net observations report
by GCN Circulars 13 Aug '25

13 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41337 SUBJECT: IceCube Alert 250813.14: Global MASTER-Net observations report DATE: 25/08/13 07:40:23 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A.Sosnovskij (CrAO), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-OAFA robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Argentina (OAFA observatory of San Juan National University) started inspect of the IceCube Alert 250813.14 (trigger No 9390028,18h 21m 25.68s , +08d 35m 38.4s, R=1.46) errorbox 28 sec after notice time and 83 sec after trigger time at 2025-08-13 03:22:33 UT, with upper limit up to 18.9 mag. The observations began at zenith distance = 48 deg. The sun altitude is -66.0 deg. The galactic latitude b = 10 deg., longitude l = 38 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2967299 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 93 | 2025-08-13 03:22:33 | MASTER-OAFA | (18h 21m 47.85s , +08d 34m 54.8s) | C | 20 | 18.0 | 178 | 2025-08-13 03:22:33 | MASTER-OAFA | (18h 21m 47.86s , +08d 34m 54.7s) | C | 190 | 18.6 | Coadd 119 | 2025-08-13 03:22:58 | MASTER-OAFA | (18h 21m 47.86s , +08d 34m 56.2s) | C | 20 | 18.0 | 150 | 2025-08-13 03:23:24 | MASTER-OAFA | (18h 21m 47.87s , +08d 34m 57.4s) | C | 30 | 18.0 | 186 | 2025-08-13 03:24:00 | MASTER-OAFA | (18h 21m 47.85s , +08d 34m 58.9s) | C | 30 | 17.8 | 227 | 2025-08-13 03:24:36 | MASTER-OAFA | (18h 21m 47.85s , +08d 35m 00.1s) | C | 40 | 17.9 | 278 | 2025-08-13 03:25:22 | MASTER-OAFA | (18h 21m 47.86s , +08d 35m 01.4s) | C | 50 | 18.3 | 339 | 2025-08-13 03:26:18 | MASTER-OAFA | (18h 21m 47.84s , +08d 35m 03.0s) | C | 60 | 18.2 | 409 | 2025-08-13 03:27:24 | MASTER-OAFA | (18h 21m 47.82s , +08d 35m 04.7s) | C | 70 | 18.3 | 495 | 2025-08-13 03:28:40 | MASTER-OAFA | (18h 21m 47.81s , +08d 35m 06.6s) | C | 90 | 18.5 | 601 | 2025-08-13 03:30:15 | MASTER-OAFA | (18h 21m 47.78s , +08d 35m 08.8s) | C | 110 | 18.5 | 721 | 2025-08-13 03:30:15 | MASTER-OAFA | (18h 21m 47.78s , +08d 35m 08.8s) | C | 350 | 18.9 | Coadd 723 | 2025-08-13 03:32:12 | MASTER-OAFA | (18h 21m 47.74s , +08d 35m 10.8s) | C | 120 | 18.6 | 849 | 2025-08-13 03:34:18 | MASTER-OAFA | (18h 21m 47.74s , +08d 35m 13.1s) | C | 120 | 18.6 | 975 | 2025-08-13 03:36:24 | MASTER-OAFA | (18h 21m 47.74s , +08d 35m 15.2s) | C | 120 | 18.7 | 1101 | 2025-08-13 03:38:30 | MASTER-OAFA | (18h 21m 47.72s , +08d 35m 17.0s) | C | 120 | 18.7 | 1227 | 2025-08-13 03:40:36 | MASTER-OAFA | (18h 21m 47.69s , +08d 35m 18.6s) | C | 120 | 18.7 | 1353 | 2025-08-13 03:42:43 | MASTER-OAFA | (18h 21m 47.69s , +08d 35m 20.0s) | C | 120 | 18.6 | 1480 | 2025-08-13 03:44:49 | MASTER-OAFA | (18h 21m 47.67s , +08d 35m 21.5s) | C | 120 | 18.7 | 1606 | 2025-08-13 03:46:55 | MASTER-OAFA | (18h 21m 47.64s , +08d 35m 22.7s) | C | 120 | 18.6 | 1732 | 2025-08-13 03:49:01 | MASTER-OAFA | (18h 21m 47.63s , +08d 35m 24.1s) | C | 120 | 18.7 | 1858 | 2025-08-13 03:51:07 | MASTER-OAFA | (18h 21m 47.60s , +08d 35m 25.4s) | C | 120 | 18.7 | 1984 | 2025-08-13 03:53:13 | MASTER-OAFA | (18h 21m 47.57s , +08d 35m 26.4s) | C | 120 | 18.8 | 2110 | 2025-08-13 03:55:19 | MASTER-OAFA | (18h 21m 47.55s , +08d 35m 27.4s) | C | 120 | 18.7 | 2236 | 2025-08-13 03:57:25 | MASTER-OAFA | (18h 21m 47.49s , +08d 35m 28.2s) | C | 120 | 18.7 | 2362 | 2025-08-13 03:59:31 | MASTER-OAFA | (18h 21m 47.45s , +08d 35m 29.1s) | C | 120 | 18.7 | 2488 | 2025-08-13 04:01:37 | MASTER-OAFA | (18h 21m 47.41s , +08d 35m 30.3s) | C | 120 | 18.7 | 2614 | 2025-08-13 04:03:43 | MASTER-OAFA | (18h 21m 47.40s , +08d 35m 31.3s) | C | 120 | 18.5 | 2740 | 2025-08-13 04:05:49 | MASTER-OAFA | (18h 21m 47.39s , +08d 35m 32.2s) | C | 120 | 18.3 | 2866 | 2025-08-13 04:07:56 | MASTER-OAFA | (18h 21m 47.39s , +08d 35m 33.2s) | C | 120 | 18.6 | 2993 | 2025-08-13 04:10:02 | MASTER-OAFA | (18h 21m 47.38s , +08d 35m 33.6s) | C | 120 | 18.6 | 3119 | 2025-08-13 04:12:09 | MASTER-OAFA | (18h 21m 47.39s , +08d 35m 34.5s) | C | 120 | 18.5 | 3246 | 2025-08-13 04:14:15 | MASTER-OAFA | (18h 21m 47.36s , +08d 35m 35.2s) | C | 120 | 18.6 | 3371 | 2025-08-13 04:16:21 | MASTER-OAFA | (18h 21m 47.35s , +08d 35m 35.8s) | C | 120 | 18.6 | 3497 | 2025-08-13 04:18:27 | MASTER-OAFA | (18h 21m 47.33s , +08d 35m 36.2s) | C | 120 | 18.7 | 3623 | 2025-08-13 04:20:33 | MASTER-OAFA | (18h 21m 47.31s , +08d 35m 36.5s) | C | 120 | 18.7 | 3749 | 2025-08-13 04:22:39 | MASTER-OAFA | (18h 21m 47.27s , +08d 35m 36.5s) | C | 120 | 18.6 | 3875 | 2025-08-13 04:24:45 | MASTER-OAFA | (18h 21m 47.24s , +08d 35m 36.8s) | C | 120 | 18.7 | 4001 | 2025-08-13 04:26:50 | MASTER-OAFA | (18h 21m 47.21s , +08d 35m 37.3s) | C | 120 | 18.7 | 4121 | 2025-08-13 04:26:50 | MASTER-OAFA | (18h 21m 47.21s , +08d 35m 37.3s) | C | 360 | 18.9 | Coadd 4127 | 2025-08-13 04:28:57 | MASTER-OAFA | (18h 21m 47.19s , +08d 35m 37.5s) | C | 120 | 18.7 | 4254 | 2025-08-13 04:31:03 | MASTER-OAFA | (18h 21m 47.21s , +08d 35m 38.2s) | C | 120 | 18.6 | 4380 | 2025-08-13 04:33:09 | MASTER-OAFA | (18h 21m 47.19s , +08d 35m 38.3s) | C | 120 | 18.5 | 4500 | 2025-08-13 04:33:09 | MASTER-OAFA | (18h 21m 47.19s , +08d 35m 38.3s) | C | 360 | 18.8 | Coadd 4507 | 2025-08-13 04:35:16 | MASTER-OAFA | (18h 21m 47.17s , +08d 35m 38.4s) | C | 120 | 18.6 | 4633 | 2025-08-13 04:37:22 | MASTER-OAFA | (18h 21m 47.16s , +08d 35m 38.9s) | C | 120 | 18.5 | 4759 | 2025-08-13 04:39:28 | MASTER-OAFA | (18h 21m 47.15s , +08d 35m 39.2s) | C | 120 | 18.6 | 4885 | 2025-08-13 04:41:34 | MASTER-OAFA | (18h 21m 47.16s , +08d 35m 39.5s) | C | 120 | 18.5 | 5011 | 2025-08-13 04:43:40 | MASTER-OAFA | (18h 21m 47.10s , +08d 35m 39.6s) | C | 120 | 18.6 | 5137 | 2025-08-13 04:45:46 | MASTER-OAFA | (18h 21m 47.07s , +08d 35m 39.2s) | C | 120 | 18.5 | 5263 | 2025-08-13 04:47:52 | MASTER-OAFA | (18h 21m 47.02s , +08d 35m 39.0s) | C | 120 | 18.5 | 5389 | 2025-08-13 04:49:58 | MASTER-OAFA | (18h 21m 46.99s , +08d 35m 38.8s) | C | 120 | 18.5 | 5515 | 2025-08-13 04:52:04 | MASTER-OAFA | (18h 21m 46.99s , +08d 35m 38.5s) | C | 120 | 18.6 | 5635 | 2025-08-13 04:52:04 | MASTER-OAFA | (18h 21m 47.00s , +08d 35m 38.5s) | C | 360 | 18.8 | Coadd 5641 | 2025-08-13 04:54:10 | MASTER-OAFA | (18h 21m 47.00s , +08d 35m 38.3s) | C | 120 | 18.6 | 5767 | 2025-08-13 04:56:16 | MASTER-OAFA | (18h 21m 46.96s , +08d 35m 38.2s) | C | 120 | 18.5 | 5893 | 2025-08-13 04:58:23 | MASTER-OAFA | (18h 21m 46.95s , +08d 35m 38.0s) | C | 120 | 18.6 | 6013 | 2025-08-13 04:58:23 | MASTER-OAFA | (18h 21m 46.95s , +08d 35m 38.0s) | C | 360 | 18.9 | Coadd 6019 | 2025-08-13 05:00:28 | MASTER-OAFA | (18h 21m 46.94s , +08d 35m 38.1s) | C | 120 | 18.6 | 6145 | 2025-08-13 05:02:34 | MASTER-OAFA | (18h 21m 46.93s , +08d 35m 37.9s) | C | 120 | 18.6 | 6271 | 2025-08-13 05:04:40 | MASTER-OAFA | (18h 21m 46.92s , +08d 35m 38.0s) | C | 120 | 18.5 | 6397 | 2025-08-13 05:06:47 | MASTER-OAFA | (18h 21m 46.90s , +08d 35m 37.8s) | C | 120 | 18.4 | 6524 | 2025-08-13 05:08:53 | MASTER-OAFA | (18h 21m 46.89s , +08d 35m 37.7s) | C | 120 | 18.4 | 6649 | 2025-08-13 05:10:59 | MASTER-OAFA | (18h 21m 46.88s , +08d 35m 37.3s) | C | 120 | 18.3 | 6775 | 2025-08-13 05:13:04 | MASTER-OAFA | (18h 21m 46.85s , +08d 35m 36.9s) | C | 120 | 18.5 | 6901 | 2025-08-13 05:15:11 | MASTER-OAFA | (18h 21m 46.82s , +08d 35m 36.5s) | C | 120 | 18.5 | 7028 | 2025-08-13 05:17:17 | MASTER-OAFA | (18h 21m 46.79s , +08d 35m 36.5s) | C | 120 | 18.5 | 7154 | 2025-08-13 05:19:23 | MASTER-OAFA | (18h 21m 46.81s , +08d 35m 36.2s) | C | 120 | 18.5 | 7280 | 2025-08-13 05:21:29 | MASTER-OAFA | (18h 21m 46.78s , +08d 35m 36.1s) | C | 120 | 18.3 | 7406 | 2025-08-13 05:23:35 | MASTER-OAFA | (18h 21m 46.78s , +08d 35m 35.8s) | C | 120 | 18.3 | 7526 | 2025-08-13 05:23:35 | MASTER-OAFA | (18h 21m 46.78s , +08d 35m 35.7s) | C | 360 | 18.7 | Coadd 7532 | 2025-08-13 05:25:41 | MASTER-OAFA | (18h 21m 46.79s , +08d 35m 35.0s) | C | 120 | 18.4 | 7658 | 2025-08-13 05:27:47 | MASTER-OAFA | (18h 21m 46.76s , +08d 35m 34.5s) | C | 120 | 18.4 | 7784 | 2025-08-13 05:29:53 | MASTER-OAFA | (18h 21m 46.72s , +08d 35m 34.2s) | C | 120 | 18.3 | 7910 | 2025-08-13 05:31:59 | MASTER-OAFA | (18h 21m 46.68s , +08d 35m 33.9s) | C | 120 | 18.2 | 8036 | 2025-08-13 05:34:05 | MASTER-OAFA | (18h 21m 46.65s , +08d 35m 32.9s) | C | 120 | 18.1 | 8162 | 2025-08-13 05:36:11 | MASTER-OAFA | (18h 21m 46.61s , +08d 35m 32.0s) | C | 120 | 18.2 | 8282 | 2025-08-13 05:36:11 | MASTER-OAFA | (18h 21m 46.61s , +08d 35m 32.1s) | C | 360 | 18.5 | Coadd 8288 | 2025-08-13 05:38:17 | MASTER-OAFA | (18h 21m 46.58s , +08d 35m 32.0s) | C | 120 | 18.2 | 8414 | 2025-08-13 05:40:23 | MASTER-OAFA | (18h 21m 46.55s , +08d 35m 31.9s) | C | 120 | 18.2 | 8540 | 2025-08-13 05:42:29 | MASTER-OAFA | (18h 21m 46.53s , +08d 35m 31.4s) | C | 120 | 18.0 | 8660 | 2025-08-13 05:42:29 | MASTER-OAFA | (18h 21m 46.52s , +08d 35m 31.5s) | C | 360 | 18.3 | Coadd 8666 | 2025-08-13 05:44:35 | MASTER-OAFA | (18h 21m 46.47s , +08d 35m 31.7s) | C | 120 | 17.9 | 8792 | 2025-08-13 05:46:41 | MASTER-OAFA | (18h 21m 46.41s , +08d 35m 31.3s) | C | 120 | 17.8 | 8919 | 2025-08-13 05:48:48 | MASTER-OAFA | (18h 21m 46.37s , +08d 35m 30.5s) | C | 120 | 17.8 | 9039 | 2025-08-13 05:48:48 | MASTER-OAFA | (18h 21m 46.38s , +08d 35m 30.5s) | C | 360 | 18.1 | Coadd 9044 | 2025-08-13 05:50:54 | MASTER-OAFA | (18h 21m 46.34s , +08d 35m 30.0s) | C | 120 | 17.8 | 9171 | 2025-08-13 05:53:00 | MASTER-OAFA | (18h 21m 46.27s , +08d 35m 29.3s) | C | 120 | 17.7 | 9297 | 2025-08-13 05:55:06 | MASTER-OAFA | (18h 21m 46.19s , +08d 35m 28.6s) | C | 120 | 17.6 | 9423 | 2025-08-13 05:57:12 | MASTER-OAFA | (18h 21m 46.14s , +08d 35m 27.6s) | C | 120 | 17.6 | 9549 | 2025-08-13 05:59:18 | MASTER-OAFA | (18h 21m 46.09s , +08d 35m 26.7s) | C | 120 | 17.5 | 9675 | 2025-08-13 06:01:24 | MASTER-OAFA | (18h 21m 46.10s , +08d 35m 25.6s) | C | 120 | 17.2 | 9795 | 2025-08-13 06:01:24 | MASTER-OAFA | (18h 21m 46.10s , +08d 35m 25.6s) | C | 360 | 17.5 | Coadd 9801 | 2025-08-13 06:03:30 | MASTER-OAFA | (18h 21m 46.07s , +08d 35m 25.2s) | C | 120 | 17.0 | 9927 | 2025-08-13 06:05:36 | MASTER-OAFA | (18h 21m 46.11s , +08d 35m 23.9s) | C | 120 | 17.0 | 10053 | 2025-08-13 06:07:42 | MASTER-OAFA | (18h 21m 46.06s , +08d 35m 23.1s) | C | 120 | 17.0 | 10179 | 2025-08-13 06:09:49 | MASTER-OAFA | (18h 21m 46.04s , +08d 35m 22.4s) | C | 120 | 17.0 | 10306 | 2025-08-13 06:11:55 | MASTER-OAFA | (18h 21m 45.97s , +08d 35m 22.0s) | C | 120 | 16.7 | 10432 | 2025-08-13 06:14:01 | MASTER-OAFA | (18h 21m 45.92s , +08d 35m 21.4s) | C | 120 | 16.3 | 10558 | 2025-08-13 06:16:07 | MASTER-OAFA | (18h 21m 45.87s , +08d 35m 20.9s) | C | 120 | 15.6 | 10684 | 2025-08-13 06:18:13 | MASTER-OAFA | (18h 21m 45.92s , +08d 35m 19.9s) | C | 120 | 14.8 | 10810 | 2025-08-13 06:20:19 | MASTER-OAFA | (18h 21m 45.96s , +08d 35m 18.0s) | C | 120 | 14.4 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. View this GCN Circular online at https://gcn.nasa.gov/circulars/41337. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39396] LIGO/Virgo/KAGRA S250813k: Identification of a GW compact binary merger candidate
by GCN Circulars 13 Aug '25

13 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41336 SUBJECT: LIGO/Virgo/KAGRA S250813k: Identification of a GW compact binary merger candidate DATE: 25/08/13 02:36:38 GMT FROM: neil.lu(a)ligo.org The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report: We identified the compact binary merger candidate S250813k during real-time processing of data from LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) at 2025-08-13 02:12:00.444 UTC (GPS time: 1439086338.444). The candidate was found by the cWB [1], GstLAL [2], MBTA [3], MLy [4], PyCBC Live [5], and SPIIR [6] analysis pipelines. S250813k is an event of interest because its false alarm rate, as estimated by the online analysis, is 1.3e-10 Hz, or about one in 1e2 years. The event's properties can be found at this URL: https://gracedb.ligo.org/superevents/S250813k The classification of the GW signal, in order of descending probability, is BBH (>99%), Terrestrial (<1%), BNS (<1%), or NSBH (<1%). Assuming the candidate is astrophysical in origin, the probability that at least one of the compact objects is consistent with a neutron star mass (HasNS) is <1%. [7] Using the masses and spins inferred from the signal, the probability of matter outside the final compact object (HasRemnant) is <1%. [7] Both HasNS and HasRemnant consider the support of several neutron star equations of state for maximum neutron star mass. The probability that either of the binary components lies between 3 and 5 solar masses (HasMassGap) is <1%. The source chirp mass falls with highest probability in the bin (22.0, 44.0) solar masses, assuming the candidate is astrophysical in origin. Two sky maps are available at this time and can be retrieved from the GraceDB event page: * bayestar.multiorder.fits,0, an initial localization generated by BAYESTAR [8], distributed via GCN and SCiMMA notices about 24 seconds after the candidate event time. * bayestar.multiorder.fits,1, an initial localization generated by BAYESTAR [8], distributed via GCN and SCiMMA notices about 5 minutes after the candidate event time. The preferred sky map at this time is bayestar.multiorder.fits,1. For the bayestar.multiorder.fits,1 sky map, the 90% credible region is well fit by an ellipse with an area of 21 deg2 described by the following DS9 region (right ascension, declination, semi-major axis, semi-minor axis, position angle of the semi-minor axis): icrs; ellipse(09h01m, +73d31m, 5.03d, 1.32d, 107.20d) Marginalized over the whole sky, the a posteriori luminosity distance estimate is 932 +/- 209 Mpc (a posteriori mean +/- standard deviation). For further information about analysis methodology and the contents of this alert, refer to the LIGO/Virgo/KAGRA Public Alerts User Guide https://emfollow.docs.ligo.org/. [1] Klimenko et al. PRD 93, 042004 (2016) doi:10.1103/PhysRevD.93.042004 [2] Tsukada et al. PRD 108, 043004 (2023) doi:10.1103/PhysRevD.108.043004 and Ewing et al. PRD 109, 042008 (2024) doi:10.1103/PhysRevD.109.042008 [3] Alléné et al. CQG 42, 105009 (2025) doi:10.1088/1361-6382/add234 [4] Skliris et al. PRD 110, 104034 (2024) doi:10.1103/PhysRevD.110.104034 [5] Dal Canton et al. ApJ 923, 254 (2021) doi:10.3847/1538-4357/ac2f9a [6] Chu et al. PRD 105, 024023 (2022) doi:10.1103/PhysRevD.105.024023 [7] Chatterjee et al. ApJ 896, 54 (2020) doi:10.3847/1538-4357/ab8dbe [8] Singer & Price PRD 93, 024013 (2016) doi:10.1103/PhysRevD.93.0240 View this GCN Circular online at https://gcn.nasa.gov/circulars/41336. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39395] GRB 250812A: EP-FXT counterpart detection
by GCN Circulars 13 Aug '25

13 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41335 SUBJECT: GRB 250812A: EP-FXT counterpart detection DATE: 25/08/13 01:33:04 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> H. Zhou (PMO, CAS), M.-H. Zhang and W.-D. Zhang (NAO, CAS) on behalf of the Einstein Probe (EP) team: EP-FXT performed a follow-up observation of the SVOM/ECLAIRs-detected burst GRB 250812A (SVOM/sb25081201, Xin et al. GCN 41322) at 2025-08-12T04:21:33 (UTC), about 1.6 hour after the SVOM/ECLAIRs trigger, with an exposure time of 3578s. One uncatalogued source is detected within the ECLAIRs error circle, and the source is spatially consistent with the counterpart reported in optical and X-ray bands (He et al. GCN 41324, Sbarrato et al. GCN 41325, Xin et al. GCN 41326, Rakotondrainibe et al. GCN 41328, Freeberg et al. GCN 41331, Evans et al. GCN 41334). Preliminary analysis on this source are automatically conducted, and details are listed as follows. Source 1: EPF_J021113.9-430953 RA (J2000): 32.8080 Dec (J2000): -43.1644 Flux: 3.76 x 10^-12 erg/s/cm2 (observed, 0.5-10 kev) Flux_err: 2.31 x 10^-13 erg/s/cm2 (1 sigma) The position uncertainty of the source is about 10 arcsec in radius (90% C.L. statistical and systematic). Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). View this GCN Circular online at https://gcn.nasa.gov/circulars/41335. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39394] GRB 250812A: Swift ToO observations
by GCN Circulars 12 Aug '25

12 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41334 SUBJECT: GRB 250812A: Swift ToO observations DATE: 25/08/12 23:14:45 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> P. A. Evans (U. Leicester) reports on behalf of the Swift team: Swift has initiated a ToO observation of the SVOM/ECLAIRs-detected event GRB 250812A. Automated analysis of the XRT data will be presented online at https://www.swift.ac.uk/ToO_GRBs/00021856 Any uncatalogued X-ray sources detected in this analysis will be reported on this website and via GCN COUNTERPART notices. These are not necessarily related to the SVOM/ECLAIRs event. Any X-ray source considered to be a probable afterglow candidate will be reported via a GCN Circular after manual consideration. Details of the XRT automated analysis methods are detailed in Evans et al. (2007, A&A, 469, 379; 2009, MNRAS, 397, 1177 and 2014, ApJS, 210, 8). This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/41334. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39393] GRB 250812A: Swift ToO observations
by GCN Circulars 12 Aug '25

12 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41334 SUBJECT: GRB 250812A: Swift ToO observations DATE: 25/08/12 23:14:45 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> P. A. Evans (U. Leicester) reports on behalf of the Swift team: Swift has initiated a ToO observation of the SVOM/ECLAIRs-detected event GRB 250812A. Automated analysis of the XRT data will be presented online at https://www.swift.ac.uk/ToO_GRBs/00021856 Any uncatalogued X-ray sources detected in this analysis will be reported on this website and via GCN COUNTERPART notices. These are not necessarily related to the SVOM/ECLAIRs event. Any X-ray source considered to be a probable afterglow candidate will be reported via a GCN Circular after manual consideration. Details of the XRT automated analysis methods are detailed in Evans et al. (2007, A&A, 469, 379; 2009, MNRAS, 397, 1177 and 2014, ApJS, 210, 8). This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/41334. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39392] GRB 250807B: Swift-BAT refined analysis
by GCN Circulars 12 Aug '25

12 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41333 SUBJECT: GRB 250807B: Swift-BAT refined analysis DATE: 25/08/12 19:39:29 GMT FROM: Mike Moss at NASA GSFC <mikejmoss3(a)gmail.com> S. D. Barthelmy (GSFC), R. Gupta (GSFC), N. J. Klingler (GSFC/UMBC/CRESSTII), H. A. Krimm (NSF), S. Laha (GSFC/UMBC), A. Y. Lien (U Tampa), C. B. Markwardt (GSFC), M. J. Moss (GSFC), D. M. Palmer (LANL), T. Parsotan (GSFC), D. Sadaula (GSFC/UMBC), T. Sakamoto (AGU) (i.e. the Swift-BAT team): Using the data set from T-60 to T+243 sec from the recent telemetry downlink, we report further analysis of BAT GRB 250807B (trigger #1340561) (Klingler, et al., GCN Circ. 41268). The BAT ground-calculated position is RA, Dec = 15.611, -59.098 deg which is RA(J2000) = 01h 02m 26.7s Dec(J2000) = -59d 05' 52.2" with an uncertainty of 2.0 arcmin, (radius, sys+stat, 90% containment). The partial coding was 64%. The mask-weighted light curve displays a complex structure with several pulses. The T90 (15-350 keV) is 104.17 +- 29.17 sec (estimated error including systematics). The time-averaged spectrum from T-51.00 to T+85.16 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.72 +- 0.12. The fluence in the 15-150 keV band is 2.5 +- 0.2 x 10^-06 erg/cm2. The 1-sec peak photon flux measured from T-48.59 sec in the 15-150 keV band is 0.9 +- 0.3 ph/cm2/sec. All the quoted errors are at the 90% confidence level. The results of the batgrbproduct analysis are available at https://swift.gsfc.nasa.gov/results/batgrbcat/BAT_refined_circular/1340561 View this GCN Circular online at https://gcn.nasa.gov/circulars/41333. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39391] EP 250812a: GOTO optical upper limit
by GCN Circulars 12 Aug '25

12 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41332 SUBJECT: EP 250812a: GOTO optical upper limit DATE: 25/08/12 17:59:49 GMT FROM: kendall.ackley(a)warwick.ac.uk K. Ackley, A. Kumar, D. O'Neill, G. Ramsay, B.Godson, B. P. Gompertz, R. Starling, M. J. Dyer, J. Lyman, K. Ulaczyk, D. Steeghs, D. K. Galloway, V. Dhillon, P. O'Brien, K. Noysena, R. Kotak, R. P. Breton, L. K. Nuttall, and J. Casares report on behalf of the GOTO collaboration: We report on observations with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022; Dyer et al. 2024) in response to EP250812a (Zhang et al. GCN 41327). Three targeted observations were performed by GOTO-South beginning at 14:58:30UT and continuing up to 17:23:59UT on 2025-08-12, corresponding to 1.84 hours, 3.03 hours, and 4.18 hours after trigger. Each observation consisted of 4x90 s exposures in the GOTO L-band (400-700 nm). We serendipitously observed the field by GOTO-South at 9.5 hours prior to the trigger time at 03:39:10UT on 2025-08-12, where each observation consisted of 4x45s exposures in the GOTO L-band (400-700 nm). Images were processed immediately after acquisition using the GOTO pipeline. Difference imaging was performed using deeper template observations of the same pointings. Source candidates were initially filtered using a classifier (Killestein et al. 2021) and cross-matched against a variety of contextual and minor planet catalogues. We do not identify any candidate optical counterparts at the location of the Swift-XRT afterglow candidate (Evans et al. GCN 41330) or within the EP/WXT localisation uncertainty region after the trigger time, down to a 3-sigma limiting magnitude for the three sets of observations of L >18.9 (AB), L >19.4 (AB), L >19.8 (AB). The observation at 9.5 hours prior to the trigger shows no source to a 3-sigma limit of L >18.1 mag (AB). Magnitudes were calibrated using ATLAS-REFCAT2 (Tonry et al. 2018) and are not corrected for Galactic extinction. GOTO (https://goto-observatory.org/) is a network of telescopes that is principally funded by the STFC and operated at the Roque de los Muchachos Observatory on La Palma, Spain, and Siding Spring Observatory in NSW, Australia, on behalf of a consortium including the University of Warwick, Monash University, Armagh Observatory & Planetarium, the University of Leicester, the University of Sheffield, the National Astronomical Research Institute of Thailand (NARIT), the University of Turku, the University of Portsmouth, the University of Manchester and the Instituto de Astrofisica de Canarias (IAC). View this GCN Circular online at https://gcn.nasa.gov/circulars/41332. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39390] GRB 250812A: Kilonova-Catcher optical afterglow detection
by GCN Circulars 12 Aug '25

12 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41331 SUBJECT: GRB 250812A: Kilonova-Catcher optical afterglow detection DATE: 25/08/12 17:32:39 GMT FROM: Damien Turpin at CEA-Saclay <dturpin-astro(a)hotmail.com> M. Freeberg (KNC), D. Turpin (CEA-Saclay/Irfu), C. Andrade(UMN), M. Pillas (ULiege), M. Molham (NRIAG), M. Mašek (Institute of Physics, Prague, FZU, CZ), S. Antier (OCA/IJCLAB) on behalf of the GRANDMA/Kilonova-Catcher collaboration: We observed the field of GRB 250812A (Xin et al., GCN 41322) detected by SVOM/ECLAIRs with the GRANDMA citizen science project Kilonova-catcher (KNC). Our observations were performed with the iTelescope T72 telescope operated by M. Freeberg. Our observations started at T0+1.8hr. In our stacked frames, subtracted from the Legacy Survey DR10 template image, we detect an uncatalogued optical source at a position consistent with the TRT (He et al., GCN 41324), SVOM/VT (Xin et al., GCN 41326) and SVOM/COLIBRÍ (FM-GFT) (Rakotondrainibe et al., GCN 41328) optical afterglow candidate as well as the Swift/XRT (Sbarrato et al., GCN41325) x-ray afterglow candidate . We report our follow-up results in the table below: +---------------+-----------+-----------+----------------+------------+ | Tmid-TGRB (hr)| Exp (s) | Filter | Magnitude | Instrument | +===============+===========+===========+================+============+ | 2.3 | 10 x 300s | Rc (Vega) | 18.60 +/- 0.06 | iT72 | | 12.4 | 20 x 180s | Rc (Vega) | 19.12 +/- 0.11 | iT72 | +---------------+-----------+-----------+----------------+------------+ Our observations clearly show a fading behavior as also shown by the TRT and SVOM/VT observations (He et al., GCN 41324; Xin et al., GCN 41326). Thus we also suggest this source to be the afterglow of GRB 250812A. All the data have been reduced by a single data processing pipeline, STDPipe (Karpov et al., 2022). Images obtained with the Johnson-cousins filters were calibrated using the GAIA DR3 synphot catalog. We use the SkyPortal application (skyportal.io) to monitor our observational campaign (Coughlin et al. 2023). GRANDMA is a worldwide telescope network (grandma.ijclab.in2p3.fr) devoted to the observation of transients in the context of multi-messenger astrophysics (Antier et al. 2020 MNRAS 497, 5518). Kilonova-Catcher (KNC) is the citizen science program of GRANDMA (http://kilonovacatcher.in2p3.fr/) View this GCN Circular online at https://gcn.nasa.gov/circulars/41331. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39389] EP250812a: Swift-XRT counterpart detection
by GCN Circulars 12 Aug '25

12 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41330 SUBJECT: EP250812a: Swift-XRT counterpart detection DATE: 25/08/12 17:22:44 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> P.A. Evans (U. Leicester), J.A. Kennea (PSU), E. Ambrosi (INAF-IASFPA) , A.P. Beardmore (U. Leicester), M.G. Bernardini (INAF-OAB), R. Brivio (INAF-OAB), D.N. Burrows (PSU), S. Campana (INAF-OAB), M. Capalbi (INAF-OAR), A. D'Ai (INAF-IASFPA), P. D'Avanzo (INAF-OAB), V. D'Elia (SSDC & INAF-OAR), S. Dichiara (PSU), M. Ferro (INAF-OAB), A. Melandri (INAF-OAR), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), M. Perri (SSDC & INAF-OAR), C. Salvaggio (INAF-OAB), T. Sbarrato (INAF-OAB), B. Sbarufatti (INAF-OAB), M.A. Williams (PSU) report on behalf of the Swift-XRT team: Swift-XRT has performed follow-up observations of the Einstein Probe/WXT-detected source EP250812a, collecting 1.7 ks of Photon Counting (PC) mode data between T0+1.5 ks and T0+3.4 ks after the trigger. A likely counterpart has been found. The position is consistent with the uncatalogued X-ray source detected by EP-FXT (Zhang et al., GCN 41327). The details of this source are: Source 1 (SWIFT J020358.1-091907): ================================== RA (J2000.0): 30.9921 = 02h 03m 58.10s Dec (J2000.0): -9.3187 = -09d 19' 07.3" Error: 3.7 (arcsec, radius, 90% confidence). Detect flag: GOOD Distance: 67 arcsec from the Einstein Probe/WXT position. Mean rate: 0.1069 +/- 0.0091 ct s^-1 Mean flux: (4.00 +/- 0.34)e-12 erg cm^-2 s^-1 Peak rate: 0.203 +/- 0.046 ct s^-1 Peak flux: (7.6 +/- 1.7)e-12 erg cm^-2 s^-1 ECF: 3.75e-11 erg cm^-2 ct^-1 assuming NH=4.71e+20 cm^-2, gamma=1.83 determined from a spectral fit. LSXPS UL: 1.5e-03 ct/sec, (0.3-10 keV) so the source is 4.4-sigma above this 3-sigma upper limit. The source may be fading, at the 2.6-sigma level. We have detected a total of 3 sources. These have been automatically classified as follows: * 1 likely counterpart * 0 candidate counterparts * 0 uncatalogued X-ray sources * 2 known X-ray sources Known X-ray sources ------------------- Source 2 (SWIFT J020340.7-092134): ================================== RA (J2000.0): 30.9196 = 02h 03m 40.70s Dec (J2000.0): -9.3596 = -09d 21' 34.6" Error: 5.8 (arcsec, radius, 90% confidence). Detect flag: GOOD Distance: 4.8 arcmin from the Einstein Probe/WXT position. Mean rate: (8.5 [+3.0, -2.5])e-3 ct s^-1 Mean flux: (2.42 [+0.87, -0.71])e-13 erg cm^-2 s^-1 Peak rate: (8.5 [+3.0, -2.5])e-3 ct s^-1 Peak flux: (2.42 [+0.87, -0.71])e-13 erg cm^-2 s^-1 ECF: 2.86e-11 erg cm^-2 ct^-1 assuming NH=4.16e+20 cm^-2, gamma=2.23 determined from a spectral fit. This matches a catalogued X-ray source LSXPS J020340.7-092134 in the LSXPS catalogue. Details: Separation: 1.0" from the XRT source Cat Rate: 4.6e-03 +/- 8.6e-04 ct s^-1 Cat Flux: 1.3e-13 +/- 2.5e-14 erg cm^-2 s^-1 (0.3-10 keV) so the source is 1.3-sigma above the catalogued flux. There is no evidence for fading. A SIMBAD object `[VV2006] J020341.0-092134' is 3.4" away. Source 4 (SWIFT J020404.7-091504): ================================== RA (J2000.0): 31.0199 = 02h 04m 04.78s Dec (J2000.0): -9.2513 = -09d 15' 04.7" Error: 5.8 (arcsec, radius, 90% confidence). Detect flag: GOOD Distance: 4.0 arcmin from the Einstein Probe/WXT position. Mean rate: (6.6 [+2.8, -2.2])e-3 ct s^-1 Mean flux: (2.14 [+0.92, -0.72])e-13 erg cm^-2 s^-1 Peak rate: (6.6 [+2.8, -2.2])e-3 ct s^-1 Peak flux: (2.14 [+0.92, -0.72])e-13 erg cm^-2 s^-1 ECF: 3.25e-11 erg cm^-2 ct^-1 assuming NH=2.48e+20 cm^-2, gamma=1.94 determined from a spectral fit. This matches a catalogued X-ray source LSXPS J020405.1-091509 in the LSXPS catalogue. Details: Separation: 7.3" from the XRT source Cat Rate: 5.6e-03 +/- 1.5e-03 ct s^-1 Cat Flux: 1.8e-13 +/- 4.9e-14 erg cm^-2 s^-1 (0.3-10 keV) so the source is 0.3-sigma above the catalogued flux. There is no evidence for fading. All fluxes are 0.3-10 keV, observed. For all flux conversions and comparisons with catalogues and upper limits from other missions, we assumed a power-law spectrum with NH=3x10^20 cm^-2 and photon index (Gamma)=1.7 unless otherwise stated. The results of the XRT-team automatic analysis of the XRT observations, including a position-specific upper limit calculator, are available at https://www.swift.ac.uk/EP/EP_FIELD00058. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/41330. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39388] Fermi Gamma-ray Burst Monitor trigger 776705265/250812644 is not a GRB
by GCN Circulars 12 Aug '25

12 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41329 SUBJECT: Fermi Gamma-ray Burst Monitor trigger 776705265/250812644 is not a GRB DATE: 25/08/12 15:49:37 GMT FROM: oindabimukherjee(a)gmail.com O. Mukherjee (USRA) reports on behalf of the Fermi Gamma-ray Burst Monitor Team: "The Fermi Gamma-ray Burst Monitor (GBM) trigger 776705265/250812644 at 15:27:40.88 UT on 12 August 2025, tentatively classified as a GRB, is in fact not due to a GRB. This trigger is likely due to local particles." View this GCN Circular online at https://gcn.nasa.gov/circulars/41329. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39387] GRB 250807A: Swift-BAT refined analysis
by GCN Circulars 12 Aug '25

12 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41318 SUBJECT: GRB 250807A: Swift-BAT refined analysis DATE: 25/08/11 14:04:39 GMT FROM: Mike Moss at NASA GSFC <mikejmoss3(a)gmail.com> R. Gupta (GSFC), S. D. Barthelmy (GSFC), N. J. Klingler (GSFC/UMBC/CRESSTII), H. A. Krimm (NSF), S. Laha (GSFC/UMBC), A. Y. Lien (U Tampa), C. B. Markwardt (GSFC), M. J. Moss (GSFC), D. M. Palmer (LANL), T. Parsotan (GSFC), D. Sadaula (GSFC/UMBC), T. Sakamoto (AGU) (i.e. the Swift-BAT team): Using the data set from T-240 to T+520 sec from the recent telemetry downlink, we report further analysis of BAT GRB 250807A (trigger #1340514) (Klingler, et al., GCN Circ. 41262). The BAT ground-calculated position is RA, Dec = 51.435, -47.882 deg which is RA(J2000) = 03h 25m 44.4s Dec(J2000) = -47d 52' 54.4" with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment). The partial coding was 72%. The mask-weighted light curve displays a complex structure with several pulses. T90 (15-350 keV) is 75.46 +- 2.19 sec (estimated error including systematics). The time-averaged spectrum from T-20.35 to T+119.49 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.32 +- 0.03. The fluence in the 15-150 keV band is 2.5 +- 0.0 x 10^-05 erg/cm2. The 1-sec peak photon flux measured from T+33.82 sec in the 15-150 keV band is 16.7 +- 0.5 ph/cm2/sec. All the quoted errors are at the 90% confidence level. The results of the batgrbproduct analysis are available at https://swift.gsfc.nasa.gov/results/batgrbcat/BAT_refined_circular/1340514 View this GCN Circular online at https://gcn.nasa.gov/circulars/41318. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39386] GRB 250812A: SVOM/COLIBRÍ (FM-GFT) optical observations
by GCN Circulars 12 Aug '25

12 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41328 SUBJECT: GRB 250812A: SVOM/COLIBRÍ (FM-GFT) optical observations DATE: 25/08/12 14:45:26 GMT FROM: Ny Avo Rakotondrainibe at LAM <nyavo.rakotobe(a)gmail.com> Ny Avo Rakotondrainibe (LAM), Diego López-Cámara (UNAM), Jean-Grégoire Ducoin (CPPM), Alan M. Watson (UNAM), Jean-Luc Atteia (IRAP), Rosa L. Becerra (U Roma), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Fredd Sánchez Álvarez (UNAM), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (OCA), Nathaniel R. Butler (ASU) , Damien Dornic (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Benjamin Schneider (LAM), Antonio de Ugarte Postigo (LAM), and L. P. Xin (NAOC): We imaged the field of the SVOM GRB 250812A (Xin et al., GCN Circ. 41322) using the DDRAGO wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope. We observed from 2025-08-12 11:47 to 11:53 UTC (from 8.86 to 8.96 hours after the trigger) and obtained 300 seconds of exposure in the i-band filter. Due to the position of the field, the observations were conducted during astronomical twilight and at an airmass of about 3.4. The data were reduced and coadded with the COLIBRÍ pipeline and analysed with STDWeb/STDPipe (Karpov 2025). The photometry was calibrated using nearby stars from the SkyMapper DR4 catalog, is in the AB system, and is not corrected for Galactic extinction. We detected the optical counterpart reported by He et al. (GCN Circ 41324) and Xin et al. (GCN Circ 41326) at a preliminary magnitude of: i = 18.89 +/- 0.05 Further observations are planned. We thank the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir and the COLIBRÍ and DDRAGO engineering teams. COLIBRÍ is an astronomical observatory developed and operated jointly by France (AMU, CNES and CNRS) and Mexico (UNAM and SECIHTI). It is located at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, Mexico. View this GCN Circular online at https://gcn.nasa.gov/circulars/41328. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39385] EP250812a: Einstein Probe detection of an X-ray transient
by GCN Circulars 12 Aug '25

12 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41327 SUBJECT: EP250812a: Einstein Probe detection of an X-ray transient DATE: 25/08/12 13:59:12 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> M.-H. Zhang (NAO,CAS), H. Zhou (PMO,CAS) and W.-D. Zhang (NAO,CAS) on behalf of the Einstein Probe (EP) team: We report on the detection of an X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP250812a. The transient triggered EP-WXT (ID: 01709198788) at 2025-08-12T13:09:44 (UTC). The WXT position of the source is R.A. = 30.979 deg, DEC = -9.305 deg (J2000) with an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic). A follow-up observation with the Follow-up X-ray Telescope (FXT) was performed automatically. Within the WXT error circle, an uncatalogued X-ray source was detected at R.A. = 30.9964 deg, DEC = -9.3206 deg (J2000) with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic). Further information will be updated when the telemetry data is received. Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). View this GCN Circular online at https://gcn.nasa.gov/circulars/41327. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39384] GRB 250812A: SVOM/VT optical afterglow confirmation
by GCN Circulars 12 Aug '25

12 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41326 SUBJECT: GRB 250812A: SVOM/VT optical afterglow confirmation DATE: 25/08/12 13:41:54 GMT FROM: Liping Xin at NAOC, SVOM <xlp(a)nao.cas.cn> L. P. Xin, H. L. Li, Y. L. Qiu, C. Wu, Y. N. Ma, Z. H. Yao, X. H. Han, J. Wang, Y. Xu, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA), Z. M. Wang (BNU) report on behalf of the SVOM/VT team. SVOM/VT performed a Target of Opportunity observation of GRB 250812A detected by SVOM/Eclairs (Xin et al., GCN 41322). The observation began at 2025-08-12T09:19:03 UTC, 6.55 hours after the trigger, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. The optical counterpart (He et al., GCN 41324) within the errorbox of Swift/XRT (Sbarrato et al., GCN 41325) was detected in both VT_R and VT_B. The magnitudes are: Mid-time (h) | exposure time (s) | band | mag (AB) | mag err ---------------|-------------------|------|----------|-------------------------------- 8.29 | 22*70 | VT_B | 19.36 | 0.02 8.29 | 22*70 | VT_R | 18.92 | 0.02 We also noticed that this source was brightening during our observations for about 0.4 magnitudes from 6.67 hours to 8.33 hours after the burst. Our photometry was not corrected for Galactic extinction. More VT follow-ups will be scheduled. The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS. View this GCN Circular online at https://gcn.nasa.gov/circulars/41326. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39383] GRB 250812A: Swift-XRT afterglow detection
by GCN Circulars 12 Aug '25

12 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41325 SUBJECT: GRB 250812A: Swift-XRT afterglow detection DATE: 25/08/12 13:34:45 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> T. Sbarrato (INAF-OAB), D.N. Burrows (PSU), M.A. Williams (PSU), S. Dichiara (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), P. D'Avanzo (INAF-OAB), M.G. Bernardini (INAF-OAB) and P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team: Swift-XRT has performed follow-up observations of GRB 250812A. We searched for X-ray sources in 977 s of Photon Counting (PC) mode data. The total exposure at the position of the afterglow (see below) is 977 s, obtained between T0+6.7 ks and T0+12.4 ks. An uncatalogued X-ray source is detected and is above the RASS 3-sigma upper limit at this position, and is therefore likely the GRB afterglow. Using 1351 s of PC mode data and 2 UVOT images, we find an enhanced XRT position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 32.80701, -43.16360 which is equivalent to: RA (J2000): 02h 11m 13.68s Dec(J2000): -43d 09' 49.0" with an uncertainty of 3.0 arcsec (radius, 90% confidence). The light curve is consistent with a constant source of mean count rate 1.5e-01 ct/sec. A power-law fit gives an index of 0.16 (+0.64, -0.16). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.97 (+0.40, -0.23). The best-fitting absorption column is consistent with the Galactic value of 1.5 x 10^20 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.1 x 10^-11 (3.2 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 1.5 (+/-6.9) x 10^20 cm^-2 Galactic foreground: 1.5 x 10^20 cm^-2 Excess significance: <1.6 sigma Photon index: 1.97 (+0.40, -0.23) The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00019994. The results of the full analysis of the XRT observations are available at https://www.swift.ac.uk/ToO_GRBs/SVOM_FIELD00028. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/41325. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39382] GRB 250812A: TRT likely optical counterpart detection
by GCN Circulars 12 Aug '25

12 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41324 SUBJECT: GRB 250812A: TRT likely optical counterpart detection DATE: 25/08/12 09:35:34 GMT FROM: J. An <jiean0813(a)foxmail.com> L.B. He (NAOC), K. Noysena, K. Chanchaiworawit, S. Tinyanont (NARIT), S.Y. Fu (HUST), J. An, X. Liu, Z.P. Zhu, S.Q. Jiang, D. Xu (NAOC) report on behalf of a large collaboration: We observed the field of GRB 250812A (Xin et al., GCN 41322), using the 0.7-m telescope of the Thai Robotic Telescope network (TRT), located at Cerro Tololo Inter-American Observatory, Chile. Observations started at 04:32:00 UTC on 2025-08-12, i.e., ~1.8 hr after the SVOM/ECLAIRs trigger and a series of frames in the r band were obtained. In our stacked image, we detect an uncatalogued source within the SVOM/ECLAIRs error circle at coordinates: R.A.(J2000) = 02:11:13.72 = 32.80715 Dec.(J2000) = -43:09:49.21 = -43.16367 with an uncertainty of ~0.5 arcsec. We measure a preliminary magnitude of r ~ 18.8, calibrated with Legacy catalog and not corrected for Galactic extinction. We suggest this is likely the optical counterpart of GRB 250812A. View this GCN Circular online at https://gcn.nasa.gov/circulars/41324. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39381] IceCube-Cascade 250809A: Upper limits from a search for additional neutrino events in IceCube
by GCN Circulars 12 Aug '25

12 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41323 SUBJECT: IceCube-Cascade 250809A: Upper limits from a search for additional neutrino events in IceCube DATE: 25/08/12 03:56:05 GMT FROM: Yuhua Yao <yyao255(a)icecube.wisc.edu> The IceCube Collaboration (http://icecube.wisc.edu/) reports: IceCube has performed a search [1] for additional track-like muon neutrino events arriving from the direction of IceCube-Cascade 250809A (https://gcn.gsfc.nasa.gov/notices_amon_icecube_cascade/141229_33703437.amon) in a time range of 1000 seconds centered on the alert event time (2025-08-09 13:49:08.550 UTC to 2025-08-09 14:05:48.550 UTC) during which IceCube was collecting good quality data. Excluding the event that prompted the alert, zero track-like events are found within the 90% containment region of IceCube-Cascade 250809A.We report a p-value of 1.00 in this time window. The IceCube sensitivity to neutrino point sources with an E^-2.5 spectrum (E^2 dN/dE at 1 TeV) within the locations spanned by the 90% spatial containment region of IceCube-Cascade 250809A is 1.4e-01 GeV cm^-2 in a 1000 second time window. 90% of events IceCube would detect from a source at this declination with an E^-2.5 spectrum have energies in the approximate energy range between 2e+02 GeV and 9e+04 GeV. A subsequent search was performed including 2 days of data centered on the alert event time (2025-08-08 13:57:28.550 UTC to 2025-08-10 13:57:28.550 UTC). In this case, we report a p-value of 0.14, consistent with no significant excess of track events. The IceCube sensitivity to neutrino point sources with an E^-2.5 spectrum (E^2 dN/dE at 1 TeV) within the locations spanned by the 90% spatial containment region of IceCube-Cascade 250809A ranges from 1.6e-01 to 1.7e-01 GeV cm^-2 in a 2 day time window. The IceCube Neutrino Observatory is a cubic-kilometer neutrino detector operating at the geographic South Pole, Antarctica. The IceCube realtime alert point of contact can be reached at roc(a)icecube.wisc.edu. [1] IceCube Collaboration, R. Abbasi et al., ApJ 910 4 (2021) View this GCN Circular online at https://gcn.nasa.gov/circulars/41323. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39380] GRB 250812A: SVOM detection of a faint long burst
by GCN Circulars 12 Aug '25

12 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41322 SUBJECT: GRB 250812A: SVOM detection of a faint long burst DATE: 25/08/12 03:53:19 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> L. P. Xin(NAOC), Z.M. Wang(BNU), W.J. Xie(NAOC), H. Goto(Kanazawa univ.) report on behalf of the SVOM mission team: At 2025-08-12T02:46:03 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 250812A (SVOM burst-id sb25081201). The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network. The burst was only detected by the Image Trigger (IMT), which produced a sequence of 2 alerts. IMT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 7.38 in the [8-120] keV energy band over a time window of 40.96 seconds starting at 2025-08-12T02:45:22. The localization of the best alert is R.A., Dec. 32.6058, -43.0702 degrees: R.A. (J2000) = 2h10m25.40s Dec. (J2000) = -43d04m12.86s with a 90% confidence level (C.L.) radius of 10.62 arcmin (including systematic error of 2 arcmin added in quadrature). Due to the detection significance being below the slew threshold, no immediate slew was performed on this burst. No X-ray observation could be performed by SVOM/MXT for the time being. No optical observation could be performed by SVOM/VT for the time being. Follow-ups with MXT and VT would be scheduled. The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. SVOM/ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC. SVOM/GRM was developed by the Institute of High Energy Physics (IHEP) of CAS. SVOM/MXT was developed jointly by CNES, CEA-IRFU, CNRS-IJCLab, University of Leicester, MPE. The Burst Advocate (BA) on shift for this alert is xlp AT nao.cas.cn. Please contact the BA by email if you require additional information. View this GCN Circular online at https://gcn.nasa.gov/circulars/41322. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39379] GRB 250809A: Swift-BAT refined analysis
by GCN Circulars 11 Aug '25

11 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41321 SUBJECT: GRB 250809A: Swift-BAT refined analysis DATE: 25/08/11 18:09:12 GMT FROM: D. R. Sadaula at NASA GSFC <dev.r.sadaula(a)nasa.gov> D. Sadaula (GSFC/UMBC), S. D. Barthelmy (GSFC), R. Gupta (GSFC), H. A. Krimm (NSF), S. Laha (GSFC/UMBC), A. Y. Lien (U Tampa), C. B. Markwardt (GSFC), M. J. Moss (GSFC), D. M. Palmer (LANL), T. Parsotan (GSFC), T. Sakamoto (AGU) (i.e. the Swift-BAT team): Using the data set from T-240 to T+962 sec from the recent telemetry downlink, we report further analysis of BAT GRB 250809A (trigger #1340954) (Parsotan, et al., GCN Circ. 41303). The BAT ground-calculated position is RA, Dec = 233.034, -53.314 deg which is RA(J2000) = 15h 32m 08.2s Dec(J2000) = -53d 18' 50.6" with an uncertainty of 1.8 arcmin, (radius, sys+stat, 90% containment). The partial coding was 96%. The BAT light curve showed a complex structure with a duration of about 32 sec. T90 (15-350 keV) is 17.79 +- 2.77 sec (estimated error including systematics). The time-averaged spectrum from T+1.01 to T+20.94 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.83 +- 0.20. The fluence in the 15-150 keV band is 3.9 +- 0.5 x 10^-07 erg/cm2. The 1-sec peak photon flux measured from T+11.58 sec in the 15-150 keV band is 0.6 +- 0.2 ph/cm2/sec. All the quoted errors are at the 90% confidence level. The results of the batgrbproduct analysis are available at https://swift.gsfc.nasa.gov/results/batgrbcat/BAT_refined_circular/1340954 View this GCN Circular online at https://gcn.nasa.gov/circulars/41321. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39378] Fermi Gamma-ray Burst Monitor trigger 776620220/250811660 is not a GRB
by GCN Circulars 11 Aug '25

11 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41320 SUBJECT: Fermi Gamma-ray Burst Monitor trigger 776620220/250811660 is not a GRB DATE: 25/08/11 17:10:25 GMT FROM: Jacob Smith at Fermi-GBM Team <jrs0118(a)uah.edu> Jacob Smith (UAH) reports on behalf of the Fermi Gamma-ray Burst Monitor Team: The Fermi Gamma-ray Burst Monitor (GBM) trigger 776620220/250811660 at 15:50:15.05 UT on 11 August 2025, tentatively classified as a GRB, is in fact not due to a GRB. This trigger is likely due to local particles. View this GCN Circular online at https://gcn.nasa.gov/circulars/41320. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39377] GRB 250309B: 1.3m DFOT Optical observations
by GCN Circulars 11 Aug '25

11 Aug '25

TITLE: GCN CIRCULAR NUMBER: 39679 SUBJECT: GRB 250309B: 1.3m DFOT Optical observations DATE: 25/03/12 06:18:47 GMT FROM: Amit Kumar Ror at ARIES <mitturor77894(a)gmail.com> Amit K. Ror, Anshika Gupta, Pranshu, Shashi B. Pandey, Kuntal Mishra (ARIES) report: We observed the field of GRB 230509B detected by the Swift and Fermi (Evans et al. 2025, GCN 39633; Fermi GBM team, GCN 39635, 39642) with the 1.3m Devasthal Fast Optical Telescope (DFOT), located at the Devasthal Observatory of the Aryabhatta Research Institute of Observational Sciences (ARIES), India. The observations were started on 2025-03-10 at 20:25:19 UT, i.e., ~ 1.53 days after the Ferm-GBM trigger. We have taken multiple frames with an exposure time of 300s in the R filter. We stacked the images after the alignment. We detected an optical afterglow reported by Stein et al. 2025 (GCN 39639) in our stacked image. We obtain the following preliminary magnitude in the stacked image: Date Start_UT T_start-T0 (days) Filter Exp time (s) Magnitude ========================================================= 2025-03-10 20:25:19 ~1.53 R 300s*24 20.36 +/- 0.10 Our detection is consistent with Stein et al. 2025 (GCN 39639); Lipunov et al. 2025 (GCN 39641); Pérez-Fournon et al. 2025 (GCN 39643); Stein et al. 2025 (GCN 39644); Moskvitin et al. 2025 (GCN 39645); Perley et al. 2025 (GCN 39646); Malesani et al. 2025 (GCN 39647); Ducoin et al. 2025 (GCN 39650); Shin et al. 2025 (GCN 39654); Moskvitin et al. 2025 (GCN 39658); Wang et al. 2025 (GCN 39661) and Guiffreda et al. 2025 (GCN 39670). The magnitude is not corrected for the Galactic extinction in the direction of the burst. Photometric calibration is performed using the standard stars from the USNO-B1.0 catalogue. This circular may be cited. View this GCN Circular online at https://gcn.nasa.gov/circulars/39679. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39376] Fermi-LAT Gamma-ray Observations of IceCube-250804A
by GCN Circulars 11 Aug '25

11 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41319 SUBJECT: Fermi-LAT Gamma-ray Observations of IceCube-250804A DATE: 25/08/11 15:13:15 GMT FROM: Simone Garrappa at Weizmann Institute of Science <simone.garrappa(a)weizmann.ac.il> S. Garrappa (Weizmann Institute of Science), L. Pfeiffer (Univ. of Wuerzburg), S. Buson (DESY, Univ. of Wuerzburg) and C. Bartolini (INFN Bari) on behalf of the Fermi-LAT collaboration: We report an analysis of observations of the vicinity of the high-energy IC250804A neutrino event (GCN 41235) with all-sky survey data from the Large Area Telescope (LAT), on board the Fermi Gamma-ray Space Telescope. The IceCube event was detected on 2025-08-04 at 20:16:26.65 UTC (T0) with J2000 position RA = 79.50 (+0.51, -0.52) deg, Decl. = 16.65 (+0.49, -0.45) deg 90% PSF containment (J2000). No cataloged gamma-ray sources are found within the 90% IC250804A localization error (4FGL-DR4; The Fourth Fermi-LAT catalog Data Release 4, The Fermi-LAT collaboration 2023, arXiv:2307.12546). We searched for the existence of intermediate (days to years) timescale emission from a new gamma-ray transient source. Preliminary analysis indicates no significant (>5sigma) new excess emission (> 100 MeV) within the IC250804A 90% confidence localization. Assuming a power-law spectrum (photon index = 2.0 fixed) for a point source at the IC250804A best-fit position, the >100 MeV flux upper limit (95% confidence) is <1.2e-10 ph cm^-2 s^-1 for ~17-years (2008-08-04 / T0), <4.0e-08 (<2.5e-07) ph cm^-2 s^-1 for a 1-month (1-day) integration time before T0. Since Fermi normally operates in an all-sky scanning mode, regular monitoring of this source will continue. For this source, the Fermi-LAT contact person is S. Garrappa (simone.garrappa at weizmann.ac.il). The Fermi LAT is a pair conversion telescope designed to cover the energy band from 20 MeV to greater than 300 GeV. It is the product of an international collaboration between NASA and DOE in the U.S. and many scientific institutions across France, Italy, Japan and Sweden. View this GCN Circular online at https://gcn.nasa.gov/circulars/41319. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39375] GRB 250807B: Swift-BAT refined analysis
by GCN Circulars 11 Aug '25

11 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41318 SUBJECT: GRB 250807B: Swift-BAT refined analysis DATE: 25/08/11 14:04:39 GMT FROM: Mike Moss at NASA GSFC <mikejmoss3(a)gmail.com> R. Gupta (GSFC), S. D. Barthelmy (GSFC), N. J. Klingler (GSFC/UMBC/CRESSTII), H. A. Krimm (NSF), S. Laha (GSFC/UMBC), A. Y. Lien (U Tampa), C. B. Markwardt (GSFC), M. J. Moss (GSFC), D. M. Palmer (LANL), T. Parsotan (GSFC), D. Sadaula (GSFC/UMBC), T. Sakamoto (AGU) (i.e. the Swift-BAT team): Using the data set from T-240 to T+520 sec from the recent telemetry downlink, we report further analysis of BAT GRB 250807A (trigger #1340514) (Klingler, et al., GCN Circ. 41262). The BAT ground-calculated position is RA, Dec = 51.435, -47.882 deg which is RA(J2000) = 03h 25m 44.4s Dec(J2000) = -47d 52' 54.4" with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment). The partial coding was 72%. The mask-weighted light curve displays a complex structure with several pulses. T90 (15-350 keV) is 75.46 +- 2.19 sec (estimated error including systematics). The time-averaged spectrum from T-20.35 to T+119.49 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.32 +- 0.03. The fluence in the 15-150 keV band is 2.5 +- 0.0 x 10^-05 erg/cm2. The 1-sec peak photon flux measured from T+33.82 sec in the 15-150 keV band is 16.7 +- 0.5 ph/cm2/sec. All the quoted errors are at the 90% confidence level. The results of the batgrbproduct analysis are available at https://swift.gsfc.nasa.gov/results/batgrbcat/BAT_refined_circular/1340514 View this GCN Circular online at https://gcn.nasa.gov/circulars/41318. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39374] LIGO/Virgo/KAGRA S250810ck: Updated Sky localization and EM Bright Classification
by GCN Circulars 11 Aug '25

11 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41317 SUBJECT: LIGO/Virgo/KAGRA S250810ck: Updated Sky localization and EM Bright Classification DATE: 25/08/11 08:16:05 GMT FROM: Soichiro Morisaki at U. of Tokyo <soichiro.morisaki(a)ligo.org> The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report: We have conducted further analysis of the LIGO Hanford Observatory (H1) and Virgo Observatory (V1) data around the time of the compact binary merger (CBC) candidate S250810ck (GCN Circular 41315). Parameter estimation has been performed using Bilby [1] and a new sky map, Bilby.multiorder.fits,0, distributed via GCN and SCiMMA notices, is available for retrieval from the GraceDB event page: https://gracedb.ligo.org/superevents/S250810ck Based on posterior support from parameter estimation [1], under the assumption that the candidate S250810ck is astrophysical in origin, the probability that at least one of the compact objects is consistent with a neutron star mass above one solar mass (HasNS) is <1%. [2] Using the masses and spins inferred from the signal, the probability of matter outside the final compact object (HasRemnant) is <1%. [2] HasRemnant is assumed to be zero when the heavier component mass is below 1 solar mass. Both HasNS and HasRemnant consider the support of several neutron star equations of state for maximum neutron star mass. The probability that either of the binary components lies between 3 and 5 solar masses (HasMassGap) is 1%. The probability that the lighter compact object is below 1 solar mass (HasSSM) is <1%. The source chirp mass falls with highest probability in the bin (5.5, 11.0) solar masses after parameter estimation [1], assuming the candidate is astrophysical in origin. For the Bilby.multiorder.fits,0 sky map, the 90% credible region is 180 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 621 +/- 129 Mpc (a posteriori mean +/- standard deviation). For further information about analysis methodology and the contents of this alert, refer to the LIGO/Virgo/KAGRA Public Alerts User Guide https://emfollow.docs.ligo.org/. [1] Ashton et al. ApJS 241, 27 (2019) doi:10.3847/1538-4365/ab06fc and Morisaki et al. PRD 108, 123040 (2023) doi:10.1103/PhysRevD.108.123040 [2] Chatterjee et al. ApJ 896, 54 (2020) doi:10.3847/1538-4357/ab8dbe View this GCN Circular online at https://gcn.nasa.gov/circulars/41317. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39373] GRB 250809A: Swift/UVOT Detection
by GCN Circulars 10 Aug '25

10 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41316 SUBJECT: GRB 250809A: Swift/UVOT Detection DATE: 25/08/10 16:51:32 GMT FROM: Paul Kuin at MSSL <npkuin(a)gmail.com> N.P.M. Kuin (UCL/MSSL) and T. M. Parsotan (GSFC) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 250809A 128 s after the BAT trigger (Parsotan et al., GCN Circ. 41303). A source consistent with the XRT position ( Evans et al. GCN Circ. 41304 ) is detected in the initial UVOT exposures. Preliminary detections and 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag v 435 755 58 17.62 +/- 0.21 b 384 1038 97 18.86 +/- 0.19 u 128 1013 452 19.57 +/- 0.21 w1 484 805 58 >18.4 m2 459 780 58 >20.1 w2 410 1064 78 >18.8 The earliest exposures were fainter; these detections are near the peak of the light curve. The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 1.919 in the direction of the burst (Schlegel et al. 1998). View this GCN Circular online at https://gcn.nasa.gov/circulars/41316. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39372] LIGO/Virgo/KAGRA S250810ck: Identification of a GW compact binary merger candidate
by GCN Circulars 10 Aug '25

10 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41315 SUBJECT: LIGO/Virgo/KAGRA S250810ck: Identification of a GW compact binary merger candidate DATE: 25/08/10 14:58:38 GMT FROM: Anna Moreso Serra at ICCUB <anna.moreso-serra(a)ligo.org> The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report: We identified the compact binary merger candidate S250810ck during real-time processing of data from LIGO Hanford Observatory (H1) and Virgo Observatory (V1) at 2025-08-10 14:23:57.336 UTC (GPS time: 1438871055.336). The candidate was found by the GstLAL [1] analysis pipeline. S250810ck is an event of interest because its false alarm rate, as estimated by the online analysis, is 5.4e-20 Hz, or about one in 1e12 years. The event's properties can be found at this URL: https://gracedb.ligo.org/superevents/S250810ck The classification of the GW signal, in order of descending probability, is BBH (>99%), NSBH (<1%), Terrestrial (<1%), or BNS (<1%). Assuming the candidate is astrophysical in origin, the probability that at least one of the compact objects is consistent with a neutron star mass (HasNS) is <1%. [2] Using the masses and spins inferred from the signal, the probability of matter outside the final compact object (HasRemnant) is <1%. [2] Both HasNS and HasRemnant consider the support of several neutron star equations of state for maximum neutron star mass. The probability that either of the binary components lies between 3 and 5 solar masses (HasMassGap) is 9%. The source chirp mass falls with highest probability in the bin (5.5, 11.0) solar masses, assuming the candidate is astrophysical in origin. Two sky maps are available at this time and can be retrieved from the GraceDB event page: * bayestar.multiorder.fits,0, an initial localization generated by BAYESTAR [3], distributed via GCN and SCiMMA notices about 25 seconds after the candidate event time. * bayestar.multiorder.fits,1, an initial localization generated by BAYESTAR [3], distributed via GCN and SCiMMA notices about 5 minutes after the candidate event time. The preferred sky map at this time is bayestar.multiorder.fits,1. For the bayestar.multiorder.fits,1 sky map, the 90% credible region is 3454 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 628 +/- 164 Mpc (a posteriori mean +/- standard deviation). For further information about analysis methodology and the contents of this alert, refer to the LIGO/Virgo/KAGRA Public Alerts User Guide https://emfollow.docs.ligo.org/. [1] Tsukada et al. PRD 108, 043004 (2023) doi:10.1103/PhysRevD.108.043004 and Ewing et al. PRD 109, 042008 (2024) doi:10.1103/PhysRevD.109.042008 [2] Chatterjee et al. ApJ 896, 54 (2020) doi:10.3847/1538-4357/ab8dbe [3] Singer & Price PRD 93, 024013 (2016) doi:10.1103/PhysRevD.93.024013 View this GCN Circular online at https://gcn.nasa.gov/circulars/41315. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39371] Corrected Swift-XRT Refined Analysis of GRB 250809A
by GCN Circulars 10 Aug '25

10 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41314 SUBJECT: Corrected Swift-XRT Refined Analysis of GRB 250809A DATE: 25/08/10 10:35:32 GMT FROM: K.L. Page at U Leicester <klp5(a)leicester.ac.uk> K.L. Page (U. Leicester) reports on behalf of the Swift-XRT team: GCN Circ. 41313 provided an incomplete automatic modelling of the XRT light-curve of GRB 250809A. The first snapshot of data is dominated by a large flare, peaking at 240 s after the BAT trigger. The underlying decay can be modelled as a power-law with alpha = 3.0 +/- 0.2. If the light curve continues to decay with a power-law decay index of 3.0, the count rate at T+24 hours will be 2.3 x 10^-8 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 5.3 x 10^-20 (1.5 x 10^-19) erg cm^-2 s^-1. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/41314. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39370] GRB 250809A: Swift-XRT refined Analysis
by GCN Circulars 10 Aug '25

10 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41313 SUBJECT: GRB 250809A: Swift-XRT refined Analysis DATE: 25/08/10 09:44:16 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> J.P. Osborne (U. Leicester), A. D'Ai (INAF-IASFPA), S. Campana (INAF-OAB), A. Melandri (INAF-OAR), M.A. Williams (PSU), S. Dichiara (PSU), J.A. Kennea (PSU), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester) and P.A. Evans report on behalf of the Swift-XRT team: We have analysed 6.7 ks of XRT data for GRB 250809A, from 113 s to 51.4 ks after the trigger. The data comprise 910 s in Windowed Timing (WT) mode (the first 8 s were taken while Swift was slewing) with the remainder in Photon Counting (PC) mode. The best available XRT position (using the promptly downlinked event data, the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue) is RA, Dec = 233.00043, -53.29626 which is equivalent to: RA (J2000): 01h 00m 00.00s Dec(J2000): -53d 00' 00.0" with an uncertainty of 3.0 arcsec (radius, 90% confidence). The light curve can be modelled with an initial rise, with a power-law index of alpha=-1.5 (NaN, NaN), followed by a break at T+281 s to an alpha of 8.0 (NaN, NaN). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 2.41 (+/-0.13). The best-fitting absorption column is 2.05 (+0.18, -0.17) x 10^22 cm^-2, in excess of the Galactic value of 8.0 x 10^21 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 4.9 x 10^-11 (1.6 x 10^-10) erg cm^-2 count^-1. A summary of the WT-mode spectrum is thus: Total column: 2.05 (+0.18, -0.17) x 10^22 cm^-2 Galactic foreground: 8.0 x 10^21 cm^-2 Excess significance: 11.9 sigma Photon index: 2.41 (+/-0.13) If the light curve continues to decay with a power-law decay index of 2.96, the count rate at T+24 hours will be 3.7 x 10^-8 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.8 x 10^-18 (6.1 x 10^-18) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01340954. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/41313. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39369] GRB 250807B: SVOM/VT optical observation
by GCN Circulars 10 Aug '25

10 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41312 SUBJECT: GRB 250807B: SVOM/VT optical observation DATE: 25/08/10 08:51:43 GMT FROM: Yinuo Ma <mayn(a)bao.ac.cn> Y. N. Ma, Z. H. Yao, L. P. Xin, Y. L. Qiu, C. Wu, H. L. Li, X. H. Han, Y. Xu, J. Wang, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA) report on behalf of the SVOM/VT team. SVOM/VT performed a Target of Opportunity observation of GRB 250807B detected by Swift/BAT (Klingler et al., GCN 41268). The observation began at 2025-08-09T19:37:17 UTC, 51.903 hours after the trigger, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. The optical counterpart (Klingler et al., GCN 41268; Goad et al., GCN 41272; van Dalen et al., GCN 41278; Giudice et al., GCN 41289; Freeberg et al., GCN 41293; Shilling et al,. GCN 41294) was detected in both VT_R and VT_B. The magnitudes are: Mid-time (h) | exposure time (s) | band | mag (AB) | mag err ---------------|-------------------|------|----------|-------- 53.83 | 24*70 | VT_B | 23.7 | 0.3 53.84 | 24*70 | VT_R | 22.9 | 0.3 Our photometry was not corrected for Galactic extinction. The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS. View this GCN Circular online at https://gcn.nasa.gov/circulars/41312. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39368] EP250807a: EP-FXT follow-up observation upper limit
by GCN Circulars 10 Aug '25

10 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41311 SUBJECT: EP250807a: EP-FXT follow-up observation upper limit DATE: 25/08/10 04:22:40 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Y. Wang (PMO, CAS), Y. Q. Zhao (USTC,PRIC), H. Q. Cheng, Z. X. Ling (NAOC) on behalf of the Einstein Probe (EP) team: EP-FXT performed a follow-up observation of EP250807a (Wang et al. GCN 41277) at 2025-08-08 10:27:06 (UTC), about 11 hours after WXT trigger, with an exposure time of 2972 s. No significant X-ray source was detected by the FXT within the WXT error circle, the flux upper limit is 7.4e-14 erg/cm^2/s in the 0.5-10 keV. Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). View this GCN Circular online at https://gcn.nasa.gov/circulars/41311. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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