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[vsnet-grb-info 39954] GRB 250919A / EP250919a: NuSTAR detection of bright prompt emission
by GCN Circulars 19 Sep '25

19 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41888 SUBJECT: GRB 250919A / EP250919a: NuSTAR detection of bright prompt emission DATE: 25/09/19 18:19:52 GMT FROM: Gaurav Waratkar at Caltech <gauravwaratkar(a)iitb.ac.in> G. Waratkar (Caltech) and B. Grefenstette (Caltech) report on behalf of the NuSTAR Search for INteresting Gamma-ray Signals (SINGS) working group: The NuSTAR SINGS working group reports the detection of prompt emission from the long-duration GRB 250919A in both the NuSTAR CsI anti-coincidence shields. This GRB was identified through a blind search using the CsI shield rates. Details of the search algorithm will be described in a future paper. The NuSTAR SINGS algorithm triggered at 2025-09-19T00:29:12.000 (with a resolution ~5-seconds). This is consistent with the detections of GRB 250919A by Fermi/GBM (Fermi GBM Team, GCN Circ. 41874), SVOM/GRM (Wang et al., GCN Circ. 41882), associated with EP250919a detected by EP/WXT (Liang et al., GCN Circ. 41879). The NuSTAR CsI shield data are recorded at 1 Hz. The burst appears to be composed of a very bright peak lasting for ~20-s, followed 75-s later by a relatively fainter burst episode lasting for ~50-s. The peak count rate is ~9000-cps over a baseline rate of ~1,000-cps during this time period. We also see clear evidence in the signal above 100 keV in the CdZnTe detectors for the first episode. The localization from the counterpart candidate (Li et al., GCN Circ. 41877; Levan et al., GCN Circ. 41883; Airasca et al., GCN Circ. 41884; Osborne et al., GCN Circ. 41885, Oates et al., GCN Circ. 41886) at RA = 298.52, Dec = -48.83 implies an offset from the NuSTAR boresight of 33-deg and the offset from the geocenter of 74-deg. Lightcurves and analysis for this GRB can be found here: https://nustarsoc.caltech.edu/NuSTAR_Public/grbs/reports/2025/250919A/ Information on NuSTAR SINGS can be found here: https://nustarsoc.caltech.edu/NuSTAR_Public/grbs/ NuSTAR is a NASA Small Explorer mission led by Caltech and managed by JPL for NASA's Science Mission Directorate in Washington. View this GCN Circular online at https://gcn.nasa.gov/circulars/41888. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39953] GRB 250918A: SVOM/GRM observation
by GCN Circulars 19 Sep '25

19 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41887 SUBJECT: GRB 250918A: SVOM/GRM observation DATE: 25/09/19 16:42:33 GMT FROM: Chenwei Wang at IHEP <cwwang(a)ihep.ac.cn> SVOM/GRM team: Chen-Wei Wang, Chao Zheng, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Feliu Lacreu (IAP), Stéphane Schanne (CEA) Report on behalf of the SVOM team: SVOM/GRM was triggered in-flight by a burst GRB 250918A (SVOM trigger reference: sb25091803) at 2025-09-18T12:32:24.000 UTC (T0), which is also detected by Fermi/GBM (Fermi GBM Team, GCN#41865). 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 34.0 +8.0/-4.0 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb250918A.png In addition, the position of this burst, as determined by Fermi/GBM (RA= 221.8, DEC= -15.9, GCN#41865), is located at about 114 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view. With this localization, the time-averaged spectrum from T0-12 to T0+30 s is best fitted by a power law function. The power law index is 2.64 +/-0.15. The event fluence (10-1000 keV) in this time interval is (3.28 +/-0.05)E-05 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/41887. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39952] GRB 250919A/EP250919A: Swift/UVOT afterglow detection
by GCN Circulars 19 Sep '25

19 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41886 SUBJECT: GRB 250919A/EP250919A: Swift/UVOT afterglow detection DATE: 25/09/19 16:03:30 GMT FROM: Samantha Oates at University of Birmingham <samantha.oates(a)alumni.ucl.ac.uk> S. R. Oates (Lancaster U.) and R. Gupta (GSFC) report on behalf of the Swift/UVOT team: Swift/UVOT has performed follow-up observations of GRB 250919A/EP250919a (Fermi GBM team GCN 41874; Liang et al., GCN 41879, Wang et al., GCN 41882). Swift/UVOT began observations in the u band 21.4ks after the detection by Fermi/GBM (Fermi GBM team GCN 41874). A source is detected consistent with the optical counterpart reported by Li et al., (GCN 41877). The preliminary detection magnitude reported below is calculated using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373). Filter T_start(s) T_stop(s) Exp(s) Mag u 21418 23150 1705 17.14+\-0.03 The magnitude in the table is not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.057 in the direction of the burst (Schlegel et al. 1998). View this GCN Circular online at https://gcn.nasa.gov/circulars/41886. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39951] GRB 250919A: Swift-XRT afterglow detection
by GCN Circulars 19 Sep '25

19 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41885 SUBJECT: GRB 250919A: Swift-XRT afterglow detection DATE: 25/09/19 14:03:29 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), M. Ferro (INAF-OAB), R. Brivio (INAF-OAB), A. D'Ai (INAF-IASFPA), S. Lanava (PSU), S. Dichiara (PSU), J.A. Kennea (PSU), A.P. Beardmore (U. Leicester) and P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team: Swift-XRT has performed follow-up observations of GRB 250919A/EP250919a. We searched for X-ray sources in 1.7 ks of Photon Counting (PC) mode data. The total exposure at the position of the afterglow (see below) is 1.7 ks, obtained between T0+21.4 ks and T0+23.1 ks, taking T0 as the Fermi trigger time. An uncatalogued X-ray source is detected within the estimated 3-sigma Einstein Probe/WXT error region (35 arcsec), also consistent with the Fermi-LAT error region, and is above the RASS 3-sigma upper limit at this position, and is therefore likely the GRB afterglow. Using 1732 s of PC mode data and 1 UVOT image, we find an enhanced XRT position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 298.55415, -48.83775 which is equivalent to: RA (J2000): 19h 54m 13.00s Dec(J2000): -48d 50' 15.9" with an uncertainty of 2.5 arcsec (radius, 90% confidence). The light curve is consistent with a constant source of mean count rate 2.3e+00 ct/sec. A power-law fit gives an index of 1.0 (+1.9, -1.0). However, given the position of this X-ray saource is consistent with the optical counterpart with a measured redshift of 1.145 (GCN 41883), as well as being above the RASS 3-sigma upper limit, we believe this to be 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 1.52 (+0.13, -0.11). The best-fitting absorption column is 6.7 (+4.1, -1.6) x 10^20 cm^-2, consistent with the Galactic value of 5.1 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 4.5 x 10^-11 (4.8 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 6.7 (+4.1, -1.6) x 10^20 cm^-2 Galactic foreground: 5.1 x 10^20 cm^-2 Excess significance: <1.6 sigma Photon index: 1.52 (+0.13, -0.11) The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/03000101. The results of the full analysis of the XRT observations are available at https://www.swift.ac.uk/EP/EP_FIELD00075. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/41885. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39950] GRB 250919A: Fermi-LAT detection
by GCN Circulars 19 Sep '25

19 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41884 SUBJECT: GRB 250919A: Fermi-LAT detection DATE: 25/09/19 09:21:09 GMT FROM: A. Holzmann Airasca at University of Trento and INFN Bari <a.holzmannairasca(a)unitn.it> A. Holzmann Airasca (UniTrento and INFN Bari), N. Di Lalla (Stanford Univ.), E. Bissaldi (Politecnico and INFN Bari), S. Lopez (CNRS / IN2P3), D. Depalo (Politecnico and INFN Bari), T. Khalil (Johannesburg Univ), R. Gupta (NASA/GSFC) and F. Longo (University and INFN, Trieste) report on behalf of the Fermi-LAT Collaboration: On September 19, 2025, Fermi-LAT detected high-energy emission from GRB 250919A, which was also detected by Fermi-GBM (trigger 779934537 / 250919020, GCN 41876), EP (GCN 41879) spatially coincident but temporally offset by 1.77 hours, SVOM/GRB (GCN 41882) and Gemini/GMOS-S (GCN 41883). The best LAT on-ground location is found to be: RA, Dec = 298.52, -48.83 (J2000) with an error radius of 0.08 deg (90 % containment, statistical error only). This was 56 deg from the LAT boresight at the time of the GBM trigger (T0 = 00:28:52.28 UT). The data from the Fermi-LAT shows a significant increase in the event rate that is spatially and temporally correlated with the GBM emission with high significance. The photon flux above 100 MeV in the time interval 0 - 1.7 ks after the GBM trigger is (1.03 ± 0.14) E-5 ph/cm2/s. The estimated photon index above 100 MeV is -1.84 ± 0.09. The highest-energy photon is a 7 GeV event which is observed ~ 980 seconds after the GBM trigger. The Fermi-LAT point of contact for this burst is Oscar Wistemar (wistemar(a)kth.se) 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/41884. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39949] EP250919a/GRB 250919A: Gemini/GMOS-S spectroscopic redshift z = 1.145
by GCN Circulars 19 Sep '25

19 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41883 SUBJECT: EP250919a/GRB 250919A: Gemini/GMOS-S spectroscopic redshift z = 1.145 DATE: 25/09/19 08:07:27 GMT FROM: Andrew Levan at Radboud University <a.levan(a)astro.ru.nl> A. J. Levan (Radboud and Warwick), J. N. D. van Dalen (Radboud), G. Corcoran (UCD), P. G. Jonker (Radboud), D. B. Malesani (DAWN/NBI and Radboud), J. A. Quirola-Vasquez (Radboud), F. E. Bauer (SSI and UTA), A. Martin-Carrillo (UCD) report on behalf of a larger collaboration: We obtained spectroscopic observations of the optical counterpart (Li et al., GCN 41877) of EP250919a (Liang et al., 41879), probably connected to GRB 250919A (Fermi GBM team, GCN 41874; Wang et al., GCN 41882; as also indicated by the consistency with the Fermi/LAT GRB localization; https://gcn.gsfc.nasa.gov/fermi_grbs.html) Observations were secured at the Gemini-South Telescope equipped with the GMOS spectrograph using grating B480, and began at 05:30 UT, approximately 3.25 hr (5 hr) after the EP (Fermi and SVOM) triggers. At this point we obtained 4x200 s observations covering the spectral range 3800-8000 AA. In the acquisition image, the optical counterpart is clearly detected with an AB magnitude r = 17.52 +- 0.02 (calibrated against nearby objects from the SkyMapper catalog, not corrected for Galactic extinction). The spectral trace is extremely bright and reveals multiple absorption features from Mg II, Mg I, Fe II, Al III, all at a common redshift of z = 1.145. We therefore suggest this is the redshift of EP250919a / GRB 250919A. We thank the staff of Gemini, in particular Karleyne Silva for the rapid execution of these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/41883. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39948] GRB 250919A: SVOM/GRM observation of a very bright GRB
by GCN Circulars 19 Sep '25

19 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41882 SUBJECT: GRB 250919A: SVOM/GRM observation of a very bright GRB DATE: 25/09/19 07:33:19 GMT FROM: Chenwei Wang at IHEP <cwwang(a)ihep.ac.cn> SVOM/GRM team: Chen-Wei Wang, Yue Huang, Shi-Jie Zheng, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Jean-Luc Atteia (IRAP) Report on behalf of the SVOM team: SVOM/GRM was triggered in-flight by a very bright burst GRB 250919A (SVOM trigger reference: sb25091901) at 2025-09-19T00:29:15.000 UTC (T0), which is also detected by Fermi/GBM (Fermi GBM Team, GCN#41874). 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 158.0 +/-6.0 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb250919A.png In addition, the position of this burst, as determined by Fermi/GBM (RA= 303.5, DEC= 49.8, GCN#41874), is located at about 84 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view, but this burst still clearly detected by ECLAIRs through the shield due to the high brightness. With this localization, the time-averaged spectrum from T0-25 to T0+270 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.14 +0.03/-0.02 and the cutoff energy, parameterized as Epeak, is 610 +52/-46 keV. The event fluence (10-1000 keV) in this time interval is (3.01 +/-0.05)E-04 erg/cm^2. The localization of GRB 250919A in the 'Amati' relation diagram is shown at: https://www.bursthub.cn//admin/static/svgrb250919A_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/41882. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39947] GRB 250919A: BALROG localization (Fermi Trigger 779934537 / GRB 250919020)
by GCN Circulars 19 Sep '25

19 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41881 SUBJECT: GRB 250919A: BALROG localization (Fermi Trigger 779934537 / GRB 250919020) DATE: 25/09/19 05:41:12 GMT FROM: Jochen Greiner at MPE <jcgrog(a)mpe.mpg.de> T. Preis (University of Innsbruck) & J. Greiner (MPE Garching) report: The public trigdat data of the Fermi Gamma-ray Burst Monitor (GBM) trigger 779934537 at 00:28:52 on 19 Sept. 2025 were automatically fitted for spectrum and sky location with BALROG (Burgess et al. 2018, MNRAS 476, 1427; Berlato et al. 2019, ApJ 873, 60). The best-fit position is: RA(2000.0) = 300.5 deg Decl.(2000.0) = -49.1 deg The 1 sigma statistical error radius is 0.3 deg. We estimate an additional systematic error of 2 deg. Further details are available at: https://grb.mpe.mpg.de/grb/GRB250919020/ The Healpix map can be downloaded from: https://grb.mpe.mpg.de/grb/GRB250919020/healpix The location parameters are available as JSON at: https://grb.mpe.mpg.de/grb/GRB250919020/json View this GCN Circular online at https://gcn.nasa.gov/circulars/41881. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39946] EP250919a: Global MASTER-Net observations report
by GCN Circulars 19 Sep '25

19 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41880 SUBJECT: EP250919a: Global MASTER-Net observations report DATE: 25/09/19 04:54:19 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) was pointed to the EP250919a ( EP Team et al., GCN 41879) errorbox 1286 sec after trigger time at 2025-09-19 02:36:21 UT, with upper limit up to 20.4 mag. The observations began at zenith distance = 28 deg. The sun altitude is -50.4 deg. MASTER-SAAO robotic telescope located in South Africa (South African Astronomical Observatory) was pointed to the EP250919a errorbox 2640 sec after trigger time at 2025-09-19 02:58:55 UT, with upper limit up to 17.7 mag. The observations began at zenith distance = 85 deg. The sun altitude is -20.6 deg. The galactic latitude b = -31 deg., longitude l = 350 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2994829 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 1317 | 2025-09-19 02:36:21 | MASTER-OAFA | (20h 01m 51.73s , -50d 10m 08.0s) | C | 60 | 20.4 | 1393 | 2025-09-19 02:37:38 | MASTER-OAFA | (20h 01m 45.42s , -50d 11m 06.5s) | C | 60 | 20.4 | 1468 | 2025-09-19 02:38:53 | MASTER-OAFA | (20h 01m 51.69s , -50d 11m 05.3s) | C | 60 | 20.4 | 1771 | 2025-09-19 02:43:56 | MASTER-OAFA | (20h 02m 12.87s , -48d 15m 58.0s) | C | 60 | 20.3 | 1848 | 2025-09-19 02:45:13 | MASTER-OAFA | (20h 02m 12.38s , -48d 14m 56.9s) | C | 60 | 20.3 | 1923 | 2025-09-19 02:46:28 | MASTER-OAFA | (20h 02m 18.99s , -48d 15m 56.3s) | C | 60 | 20.3 | 2652 | 2025-09-19 02:58:37 | MASTER-OAFA | (19h 53m 50.03s , -48d 54m 47.0s) | C | 60 | 20.1 | 2671 | 2025-09-19 02:58:55 | MASTER-SAAO | (19h 53m 22.97s , -48d 53m 39.0s) | C | 60 | 17.3 | 2731 | 2025-09-19 02:58:55 | MASTER-SAAO | (19h 53m 23.03s , -48d 53m 39.6s) | C | 180 | 17.7 | Coadd 2718 | 2025-09-19 02:59:42 | MASTER-OAFA | (19h 53m 50.12s , -48d 54m 46.3s) | C | 60 | 20.2 | 2750 | 2025-09-19 03:00:14 | MASTER-SAAO | (19h 53m 22.90s , -48d 53m 35.3s) | C | 60 | 17.2 | 2783 | 2025-09-19 03:00:48 | MASTER-OAFA | (19h 53m 50.30s , -48d 54m 45.8s) | C | 60 | 20.2 | 2829 | 2025-09-19 03:01:33 | MASTER-SAAO | (19h 53m 22.92s , -48d 53m 29.8s) | C | 60 | 16.4 | 2849 | 2025-09-19 03:01:54 | MASTER-OAFA | (19h 53m 50.44s , -48d 54m 45.2s) | C | 60 | 20.2 | 2908 | 2025-09-19 03:02:52 | MASTER-SAAO | (19h 53m 22.65s , -48d 53m 20.6s) | C | 60 | 17.0 | 2915 | 2025-09-19 03:02:59 | MASTER-OAFA | (19h 53m 50.57s , -48d 54m 44.6s) | C | 60 | 20.3 | 2980 | 2025-09-19 03:04:05 | MASTER-OAFA | (19h 53m 50.70s , -48d 54m 43.9s) | C | 60 | 20.3 | 3047 | 2025-09-19 03:05:11 | MASTER-OAFA | (19h 53m 50.85s , -48d 54m 43.5s) | C | 60 | 20.3 | 3112 | 2025-09-19 03:06:17 | MASTER-OAFA | (19h 53m 51.00s , -48d 54m 43.3s) | C | 60 | 20.2 | 3178 | 2025-09-19 03:07:22 | MASTER-OAFA | (19h 53m 51.10s , -48d 54m 42.9s) | C | 60 | 20.2 | 3244 | 2025-09-19 03:08:29 | MASTER-OAFA | (19h 53m 51.26s , -48d 54m 42.6s) | C | 60 | 20.2 | 3310 | 2025-09-19 03:09:34 | MASTER-OAFA | (19h 53m 51.38s , -48d 54m 42.1s) | C | 60 | 20.3 | 3375 | 2025-09-19 03:10:39 | MASTER-OAFA | (19h 53m 51.55s , -48d 54m 41.6s) | C | 60 | 20.2 | 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/41880. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39945] EP250919a: Einstein Probe detection of an X-ray transient
by GCN Circulars 19 Sep '25

19 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41879 SUBJECT: EP250919a: Einstein Probe detection of an X-ray transient DATE: 25/09/19 04:34:49 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Y. F. Liang (PMO), R. D. Liang, C. L. Guo, W. J. Hu, Z. X. Ling (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 EP250919a. The transient triggered EP-WXT (ID: 01709243841). A follow-up observation with the Follow-up X-ray Telescope (FXT) was performed automatically. At 2025-09-19T02:14:55 (UTC), an uncatalogued X-ray source was detected at R.A. = 298.5520 deg, DEC = -48.8395 deg (J2000) with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic). An uncataloged optical source was detected within FXT error circle (GCN 41877, 41878). EP250919a is located within the 1-sigma error region of GRB 250919A (GCN 41874). However, the temporal offset exceeds 2 hours, and thus we cannot rule out the possibility of a chance spatial coincidence. Further information will be updated when the telemetry data is received. Further follow-up observations are encouraged. 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/41879. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39944] Correction for GCN 41877: EP-WXT ID is 01709243841
by GCN Circulars 19 Sep '25

19 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41878 SUBJECT: Correction for GCN 41877: EP-WXT ID is 01709243841 DATE: 25/09/19 03:38:33 GMT FROM: Wenxiong Li at NAOC <liwenxiong1992(a)gmail.com> Wenxiong Li (NAOC), Iair Arcavi (TAU), Ido Keinan (TAU), David Sand (U of Arizona) The correct EP-WXT trigger ID in GCN 41877 is 01709243841. We apologize for any confusion. View this GCN Circular online at https://gcn.nasa.gov/circulars/41878. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39943] The EP-WXT trigger 01709240768: Las Cumbres discovery of the optical counterpart
by GCN Circulars 19 Sep '25

19 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41877 SUBJECT: The EP-WXT trigger 01709240768: Las Cumbres discovery of the optical counterpart DATE: 25/09/19 03:28:55 GMT FROM: Wenxiong Li at NAOC <liwenxiong1992(a)gmail.com> Wenxiong Li (NAOC), Iair Arcavi (TAU), Ido Keinan (TAU), David Sand (U of Arizona) We observed the position of EP-WXT trigger 01709240768 with a Las Cumbres 1m telescope at Cerro Tololo Inter-American Observatory 0.8 hours after the Einstein Probe WXT trigger. We took 2x300s exposures in the broad optical w band. We find an uncataloged source at RA=298.55383, Dec=-48.8378 within the EP/WXT error circle and measure the following preliminary photometry calibrated to the r band: MJD 60937.127 Mag 17.0 Additional followup is encouraged. View this GCN Circular online at https://gcn.nasa.gov/circulars/41877. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39942] GRB 250916A: Fermi GBM Observation
by GCN Circulars 19 Sep '25

19 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41876 SUBJECT: GRB 250916A: Fermi GBM Observation DATE: 25/09/19 02:43:19 GMT FROM: Matt Godwin <msg0028(a)uah.edu> Matt Godwin (UAH) and C. Meegan (UAH) reports on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 13:29:21.01 UT on 16 September 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250916A (trigger 779722166/250916562). which was also detected by AstroSat ( Arya et al. 2025, GCN 41843) with an optical counterpart by GOTO (Belkin et al. 2025, GCN 41847). The angle from the Fermi LAT boresight is 66 degrees. GBM triggered on what appears to be precursor and the main emission episode begins about 150 seconds after the precursor. The lightcurve has a duration (T90) of about 80 s (50-300 keV). The time-averaged spectrum of the main emission from T0+230 to T0+290 s is best fit by a Band function with Epeak = 144 +/- 9 keV, alpha = -1.08 +/- 0.03, and beta = -2.00 +/- 0.03. The event fluence (10-1000 keV) within this time interval is (4.61 +/- 0.07)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+270 s in the 10-1000 keV band is 5.65 +/- 0.4 ph/s/cm^2. The time-averaged spectrum of the percursor from T0-12 to T0+05 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -0.92 +/- 0.3 and the cutoff energy, parameterized as Epeak, is 110 +/- 22 keV. The event fluence (10-1000 keV) within this time interval is (1.31 +/- 0.15)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+270 s in the 10-1000 keV band is 0.67 +/- 0.05 ph/s/cm^2. The localization for the preliminary pulse is uncertain, but consistent with the secondary pulse. The event fluence (10-1000 keV) within the whole time interval is (4.73 +/- 0.16)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+270 s in the 10-1000 keV band is 4.57 +/- 0.3 ph/s/cm^2. The localization for the preliminary pulse is uncertain, but consistent with the secondary pulse. 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/41876. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39941] Fermi GRB 250919A: Global MASTER-Net observations report
by GCN Circulars 19 Sep '25

19 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41875 SUBJECT: Fermi GRB 250919A: Global MASTER-Net observations report DATE: 25/09/19 01:30:59 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-SAAO robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in South Africa (South African Astronomical Observatory) started inspect of the Fermi GRB 250919A ( Fermi GBM team, GCN 41874) errorbox 557 sec after notice time and 592 sec after trigger time at 2025-09-19 00:38:44 UT, with upper limit up to 19.3 mag. The observations began at zenith distance = 63 deg. The sun altitude is -47.5 deg. MASTER-OAFA robotic telescope located in Argentina (OAFA observatory of San Juan National University) started inspect of the Fermi GRB 250919A errorbox 658 sec after notice time and 693 sec after trigger time at 2025-09-19 00:40:26 UT, with upper limit up to 20.3 mag. The observations began at zenith distance = 19 deg. The sun altitude is -28.7 deg. The galactic latitude b = -34 deg., longitude l = 350 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2994728 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 622 | 2025-09-19 00:38:44 | MASTER-SAAO | (20h 12m 52.30s , -49d 54m 57.2s) | C | 60 | 19.3 | 622 | 2025-09-19 00:38:44 | MASTER-SAAO | (20h 10m 02.82s , -49d 39m 38.7s) | C | 60 | 19.2 | 764 | 2025-09-19 00:40:26 | MASTER-OAFA | (20h 13m 10.49s , -49d 55m 27.8s) | C | 140 | 20.2 | 925 | 2025-09-19 00:42:52 | MASTER-OAFA | (20h 13m 10.79s , -49d 55m 23.7s) | C | 170 | 20.3 | 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/41875. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39940] GRB 250919A: Fermi GBM Final Real-time Localization
by GCN Circulars 19 Sep '25

19 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41874 SUBJECT: GRB 250919A: Fermi GBM Final Real-time Localization DATE: 25/09/19 00:39:24 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 00:28:52 UT on 19 Sep 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250919A (trigger 779934537.284108 / 250919020). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 303.5, Dec = -49.8 (J2000 degrees, equivalent to J2000 20h 14m, -49d 47'), with a statistical uncertainty of 1.0 degrees. The angle from the Fermi LAT boresight is 57.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250919020/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250919020/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250919020/… View this GCN Circular online at https://gcn.nasa.gov/circulars/41874. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39939] GRB 250916A: KAIT optical observations
by GCN Circulars 18 Sep '25

18 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41873 SUBJECT: GRB 250916A: KAIT optical observations DATE: 25/09/18 22:13:06 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 250916A (Fermi GBM team, GCN 41839; Arya et al., GCN 41843; Cheung et al., GCN 41855; Waratkar et al., GCN 41871) starting at ~0.783d and again at ~1.738d after the burst. A set of clear (roughly R) filter images were obtained. We clearly detected the optical afterglow (Belkin et al., GCN 41847; Mohan et al., GCN 41858; Moskvitin et al., GCN 41859; Burkhonov et al., GCN 41860; de Ugarte Postigo et al., GCN 41863; Moskvitin et al., GCN 41870) in our coadd images. We estimate the afterglow to be 19.35 +/- 0.1 and 20.10 +/- 0.1 mag (Vega) at a mid time of ~0.824d and ~1.807d respectively. View this GCN Circular online at https://gcn.nasa.gov/circulars/41873. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39938] GRB 250917B: VLT/HAWK-I near-infrared observations
by GCN Circulars 18 Sep '25

18 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41872 SUBJECT: GRB 250917B: VLT/HAWK-I near-infrared observations DATE: 25/09/18 20:03:34 GMT FROM: muskan.yadav(a)students.uniroma2.eu Muskan Yadav (U. Rome), Rosa L. Becerra (U. Rome) and Eleonora Troja (U. Rome) report on behalf of the ERC BHianca team: We observed the field of GRB 250917B (Fermi GBM Team et al., GCN 41846; Caputo et al., GCN 41848) with the HAWKI imager on the ESO VLT UT4 (Yepun). Observations started on 2025-09-17 at 23:52:22 UT, approximately 0.7 days after the trigger, and were carried out in the Ks filter at an average seeing of 0.6". Image subtraction against 2MASS Catalogue (Skrutskie et al. 2006) shows no new uncataloged source down to K~18.5 AB. Several fainter objects are visible within the BAT refined position (Parsotan et al., GCN 41868), however additional observations are required to assess their variability. At the position of the Source 1 reported by Kennea et al. GCN 41851, our observation is dominated by the close bright star TYC 1059-317-1. We thank the staff at the VLT, for the rapid execution of these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/41872. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39937] GRB 250916A: NuSTAR detection of the prompt emission
by GCN Circulars 18 Sep '25

18 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41871 SUBJECT: GRB 250916A: NuSTAR detection of the prompt emission DATE: 25/09/18 19:45:02 GMT FROM: Gaurav Waratkar at Caltech <gauravwaratkar(a)iitb.ac.in> G. Waratkar (Caltech) and B. Grefenstette (Caltech) report on behalf of the NuSTAR Search for INteresting Gamma-ray Signals (SINGS) working group: The NuSTAR SINGS working group reports the detection of prompt emission from the long-duration GRB 250916A in both the NuSTAR CsI anti-coincidence shields. This GRB was identified through a blind search using the CsI shield rates. Details of the search algorithm will be described in a future paper. The NuSTAR SINGS algorithm triggered at 2025-09-16 13:33:27.000 (with a resolution ~5-seconds). This is consistent with the detections by Fermi-GBM (Fermi GBM Team, GCN Circ., 41839), Astrosat-CZTI (Arya et al., GCN Circ. 41843), Glowbug (Cheung et al., GCN Circ. 41855), and CALET-GBM (Trig ID. 1442064382). The NuSTAR CsI shield data are recorded at 1 Hz. The burst appears to be composed of two significantly-detected peaks. We do not detect the initial faint burst detected by Fermi-GBM which occurred ~250-s before our detection. The total duration for the event is at roughly 50-s. The peak count rate is ~500-cps over a baseline rate of ~1,000-cps during this time period. We do not see clear evidence in the signal above 100 keV in the CdZnTe detectors. The localization from the optical counterpart candidate (Belkin et al., GCN Circ. 41847) at RA = 26.57, Dec = 36.16 implies an offset from the NuSTAR boresight of 69-deg (e.g., through the side of the instrument) and the offset from the geocenter of 142-deg. Lightcurves and analysis for this GRB can be found here: https://nustarsoc.caltech.edu/NuSTAR_Public/grbs/reports/2025/250916A/ Information on NuSTAR SINGS can be found here: https://nustarsoc.caltech.edu/NuSTAR_Public/grbs/ NuSTAR is a NASA Small Explorer mission led by Caltech and managed by JPL for NASA's Science Mission Directorate in Washington. View this GCN Circular online at https://gcn.nasa.gov/circulars/41871. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39936] GRB 250916A: further SAO RAS optical observations
by GCN Circulars 18 Sep '25

18 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41870 SUBJECT: GRB 250916A: further SAO RAS optical observations DATE: 25/09/18 15:39:58 GMT FROM: Alexander Moskvitin at SAO RAS <mosk(a)sao.ru> A. Moskvitin (SAO RAS), A. Pozanenko (IKI), N. Pankov (HSE, IKI) report on behalf of GRB follow-up collaboration and IKI-GRB-FuN. We observed the field of the GRB 250916A (Fermi GBM team, GCN 41839; Arya et al., GCN 41843; Cheung et al., GCN 41855) with the BTA, 6-m telescope of SAO RAS equipped with SCORPIO-1 focal reducer. We obtained 3 x 60 sec. images in Rc band under mediocre weather conditions on September 18, 00:07:09--00:15:29 UT (t_mid - T0 = 1.4458 days = 34.6994 hours). The OT (Belkin et al., GCN 41847; Mohan et al., GCN 41858; Burkhonov et al., GCN 41860) at the redshift z = 2.015 (de Ugarte Postigo et al., GCN 41863) is clearly detected in the stacked frame with a brightness of R = 19.72 +/- 0.05. The preliminary photometry is based on PanSTARRS data on nearby objects (magnitudes calculated using the Lupton 2005 transformations) and does not take into account Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/41870. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39935] GRB 250912A: SVOM/ECLAIRs refined analysis
by GCN Circulars 18 Sep '25

18 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41869 SUBJECT: GRB 250912A: SVOM/ECLAIRs refined analysis DATE: 25/09/18 15:09:27 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Hui Yang, Olivier Godet, Marius Brunet, Jean-Luc Atteia (IRAP), Floriane Cangemi (APC), Jean-Grégoire Ducoin, Damien Dornic (CPPM) Using the event-by-event data downloaded through the X-band ground station, we report further analysis of ECLAIRs observations of GRB 250912A (SVOM burst-id sb25091206, GCN 41820) detected at T0 = 2025-09-12T21:06:24.69, which was also detected by SVOM/GRM (GCN 41826) and Fermi/GBM (GCN 41819). The burst that triggered ECLAIRs consists of a short main peak starting from T0-1.19 s and lasting about 0.6 s in the 4-120 keV energy band, followed by extended emission continuing until T0+18.3 s. We note a weak precursor at T0-11.1 s, detected mainly in the 8-20 keV band by ECLAIRs and also by GRM, whose position is consistent with that of the main event. The spectrum of the main peak (from T0-1.19 s to T0-0.55 s) in the 4-120 keV energy range is well fitted by a power-law model with a photon index of 1.2 +/-0.2. With this model, the 4-120 keV flux is (1.7+/-0.4)e-07 erg/cm^2/s. The spectrum of the extended emission following the main peak (from T0-0.55 s to T0+18.31 s) in the 4-120 keV band is well fitted by a power-law model with a photon index of 1.4+/-0.1, yielding a 4-120 keV flux of (3.3+/-0.5)e-08 erg/cm^2/s. The spectral index is consistent with that measured by SVOM/GRM and Fermi/GBM (GCN 41828). The combined fluence of both components in the 4-120 keV is (7.3+/-1.0)e-07 erg/cm^2. The low count rates prevent a spectral analysis of the precursor and the time-resolved spectral analysis of the burst. All the quoted errors are at the 68% confidence level. 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. ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC. The SVOM/ECLAIRs point of contact for this burst is: Hui Yang (IRAP) (hui.yang(a)irap.omp.eu) View this GCN Circular online at https://gcn.nasa.gov/circulars/41869. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39934] GRB 250917B: Swift-BAT refined analysis
by GCN Circulars 18 Sep '25

18 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41868 SUBJECT: GRB 250917B: Swift-BAT refined analysis DATE: 25/09/18 13:56:31 GMT FROM: Amy <yarleen(a)gmail.com> T. Parsotan (GSFC), S. D. Barthelmy (GSFC), R. Caputo (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), D. Sadaula (GSFC/UMBC), 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 250917B (trigger #1350381) (Caputo et al., GCN Circ. 41848). The BAT ground-calculated position is RA, Dec = 291.382, 11.117 deg which is RA(J2000) = 19h 25m 31.8s Dec(J2000) = +11d 06' 59.9" with an uncertainty of 1.4 arcmin, (radius, sys+stat, 90% containment). The partial coding was 48%. The mask-weighted light curve shows a single FRED-like structure that starts at ~T-0.1, peaks at ~T0, and ends at ~T+0.4. T90 (15-350 keV) is 0.29 +- 0.08 sec (estimated error including systematics). The time-averaged spectrum from T+0.00 to T+0.37 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.66 +- 0.17. The fluence in the 15-150 keV band is 1.7 +- 0.2 x 10^-07 erg/cm2. The 1-sec peak photon flux measured from T-0.31 sec in the 15-150 keV band is 2.4 +- 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/1350381 View this GCN Circular online at https://gcn.nasa.gov/circulars/41868. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39933] LIGO/Virgo/KAGRA S250918aw: 1 counterpart neutrino candidate event from an IceCube neutrino search
by GCN Circulars 18 Sep '25

18 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41867 SUBJECT: LIGO/Virgo/KAGRA S250918aw: 1 counterpart neutrino candidate event from an IceCube neutrino search DATE: 25/09/18 13:48:08 GMT FROM: Zsuzsa Marka at IceCube/Columbia University <zsuzsa(a)astro.columbia.edu> IceCube Collaboration (http://icecube.wisc.edu/) reports: We have performed a search for track-like muon neutrino candidate events detected by IceCube consistent with the sky localization of the low-significance gravitational-wave candidate event S250918aw in a time range of 1000 seconds centered on the alert event time (2025-09-18 07:55:35 UTC to 2025-09-18 08:12:15 UTC) [1,2]. During this time period, IceCube was collecting good quality data. A single hypothesis test was conducted using a Bayesian approach to quantify the joint GW + neutrino event significance, which assumes a binary merger scenario and accounts for known astrophysical priors, such as GW source distance, in the statistical significance estimation [3]. One track-like event was found in spatial and temporal coincidence with the gravitational-wave candidate S250918aw calculated from the map circulated in the S250918aw-2-Preliminary notice. This represents an overall p-value of 0.00023 for the Bayesian search. The p-value measures the consistency of the observed track-like events with the known atmospheric backgrounds for this single map (not accounting for statistical trials from multiple GW events). Further details are available at https://gcn.nasa.gov/missions/icecube and at https://roc.icecube.wisc.edu/public/LvkNuTrackSearch. Properties of the coincident event are shown below: dt(s) RA(deg) Dec(deg) Angular uncertainty(deg) p-value(Bayesian) ------------------------------------------------------------------------------------- -74.35 159.8 44.3 0.66 0.00023 where: dt = Time of track event minus time of GW trigger (sec) Angular uncertainty = Angular uncertainty of track event: the radius of a circle representing 90% CL containment by area. p-value = the individual p-value for the specific track event from this search. 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] M. G. Aartsen et al 2020 ApJL 898 L10 [2] Abbasi et al. Astrophys.J. 944 (2023) 1, 80 [3] I. Bartos et al. 2019 Phys. Rev. D 100, 083017 View this GCN Circular online at https://gcn.nasa.gov/circulars/41867. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39932] GRB 250918A: BALROG localization (Fermi Trigger 779891543 / GRB 250918522)
by GCN Circulars 18 Sep '25

18 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41866 SUBJECT: GRB 250918A: BALROG localization (Fermi Trigger 779891543 / GRB 250918522) DATE: 25/09/18 13:33:35 GMT FROM: Jochen Greiner at MPE <jcgrog(a)mpe.mpg.de> T. Preis (University of Innsbruck) & J. Greiner (MPE Garching) report: The public trigdat data of the Fermi Gamma-ray Burst Monitor (GBM) trigger 779891543 at 12:32:18 on 18 Sept. 2025 were automatically fitted for spectrum and sky location with BALROG (Burgess et al. 2018, MNRAS 476, 1427; Berlato et al. 2019, ApJ 873, 60). The best-fit position is: RA(2000.0) = 225.6 deg Decl.(2000.0) = -16.2 deg The 1 sigma statistical error radius is 4.1 deg. We estimate an additional systematic error of 2 deg. Further details are available at: https://grb.mpe.mpg.de/grb/GRB250918522/ The Healpix map can be downloaded from: https://grb.mpe.mpg.de/grb/GRB250918522/healpix The location parameters are available as JSON at: https://grb.mpe.mpg.de/grb/GRB250918522/json View this GCN Circular online at https://gcn.nasa.gov/circulars/41866. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39931] GRB 250918A: Fermi GBM Final Real-time Localization
by GCN Circulars 18 Sep '25

18 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41865 SUBJECT: GRB 250918A: Fermi GBM Final Real-time Localization DATE: 25/09/18 12:42:57 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 12:32:18 UT on 18 Sep 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250918A (trigger 779891543.0931 / 250918522). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 221.8, Dec = -15.9 (J2000 degrees, equivalent to J2000 14h 47m, -15d 54'), with a statistical uncertainty of 3.4 degrees. The angle from the Fermi LAT boresight is 93.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250918522/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250918522/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250918522/… View this GCN Circular online at https://gcn.nasa.gov/circulars/41865. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39930] GRB 250917B: Swift/UVOT Upper Limits
by GCN Circulars 18 Sep '25

18 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41864 SUBJECT: GRB 250917B: Swift/UVOT Upper Limits DATE: 25/09/18 11:35:38 GMT FROM: Alice Breeveld at MSSL-UCL <a.breeveld(a)ucl.ac.uk> A.A. Breeveld (UCL-MSSL) and R. Caputo (GSFC) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 250917B 139 s after the Swift/BAT trigger (Caputo et al., GCN Circ. 41848) and the Fermi GBM trigger (Fermi GBM Team, GCN 41846). No optical afterglow consistent sources 1, 5 or 6 identified by the Swift-XRT (Kennea et al., GCN Circ. 41851) is detected in the initial UVOT exposures. Preliminary 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first finding chart (FC) exposure and subsequent exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag white_FC 139 289 147 >20.5 u_FC 351 601 246 >19.9 white 139 5391 492 >21.2 v 681 1059 39 >18.1 b 606 5225 236 >20.1 u 351 5020 462 >20.1 w1 730 4815 216 >18.9 m2 705 1084 39 >18.8 w2 831 1035 39 >19.0 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 1.983 in the direction of the burst (Schlegel et al. 1998). View this GCN Circular online at https://gcn.nasa.gov/circulars/41864. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39929] GRB 250916A: OSIRIS+/GTC redshift z = 2.015
by GCN Circulars 18 Sep '25

18 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41863 SUBJECT: GRB 250916A: OSIRIS+/GTC redshift z = 2.015 DATE: 25/09/18 10:56:55 GMT FROM: Antonio de Ugarte Postigo at LAM, CNRS <adeugartepostigo(a)gmail.com> A. de Ugarte Postigo (LAM), D. B. Malesani (DAWN/NBI and Radboud), A. Martin-Carrillo (UCD), J. F. Agui Fernandez (CAHA), C. C. Thoene (AbAO), M. A. Aloy (UV), J. P. U. Fynbo (DAWN/NBI), L. Galbany (IEEC-CSIC), S. Geier (GTC), L. Izzo (INAF/OACN and DARK/NBI), G. Lombardi (GTC), N. A. Rakotondrainibe (LAM), B. Schneider (LAM), N. R. Tanvir (Univ. Leicester), F. Pérez Toledo (GTC) and D. González Gonzalez (GTC) report: We observed the optical afterglow (Belkin et al., GCN 41847) of GRB 250916A (Fermi GBM team, GCN 41839) with OSIRIS+, mounted on the 10.4 m GTC telescope, at Roque de los Muchachos Observatory, on the island of La Palma (Spain). The observation consisted of an r-band acquisition image followed by 3x900 s of spectroscopy using grism R1000B, with a spectral coverage between 3600 and 7800 AA and a resolving power of ~600. The observation started at 2025-09-18 04:15:12.011 UT (1.61 days after the burst onset). In the acquisition image we detect the afterglow at r = 20.0 +/- 0.1 mag (AB), as compared to Pan-STARRS field stars and not corrected by Galactic extinction. The spectrum shows a clear continuum over the entire spectral range. The spectrum continuum shows a moderate curvature, which could be indicative of host galaxy extinction. We detect multiple spectral features that correspond to Lyman alpha, S II, Si II, Si II*, O I, C II, Ni II, Ni II*, Si IV, C IV, Fe II, Fe II*, Al II, Al III, Cr II, Zn II, and Mn II, all at a common redshift of 2.015, which we identify as the redshift of the GRB. We also note the presence of at least one intervening system with C IV features at z = 1.853. View this GCN Circular online at https://gcn.nasa.gov/circulars/41863. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39928] GRB 250916A: Swift-XRT observations
by GCN Circulars 18 Sep '25

18 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41862 SUBJECT: GRB 250916A: Swift-XRT observations DATE: 25/09/18 07:58:29 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), C. Salvaggio (INAF-OAB), M. Ferro (INAF-OAB), R. Brivio (INAF-OAB), D.N. Burrows (PSU), S. Lanava (PSU), S. Dichiara (PSU) and P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team: Swift-XRT has performed follow-up observations of the Fermi/GBM-detected burst GRB 250916A, collecting 1.6 ks of Photon Counting (PC) mode data between T0+101.9 ks and T0+107.2 ks. One uncatalogued X-ray source has been detected within the estimated 3-sigma GOTO error region (0.8 arcsec) given in GCN Circ. 41847, it is below the RASS limit and shows no definitive signs of fading. However, given its coincident location with the fading optical source, it is indeed likely to be the afterglow. Details of this source are given below: Source 1: RA (J2000.0): 26.5708 = 01h 46m 16.99s Dec (J2000.0): +36.1652 = +36d 09' 54.6" Error: 3.7 arcsec (radius, 90% conf. [Enhanced position]) Count-rate: 0.0274 +/- 0.0049 ct s^-1 Distance: 2 arcsec from GOTO position. Flux: (9.2 +/- 1.6)e-13 erg cm^-2 s^-1 (observed, 0.3-10 keV) An uncatalogued source was also detected, however this was too far from the GRB position to be the afterglow. 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/ToO_GRBs/00021859. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/41862. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39927] EP250916a: EP-FXT follow-up observation
by GCN Circulars 18 Sep '25

18 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41861 SUBJECT: EP250916a: EP-FXT follow-up observation DATE: 25/09/18 07:46:30 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> C. Y. Dai (NJU), Q. Y. Wu, D. Y. Li, H. W. Pan (NAO, CAS) on behalf of the Einstein Probe (EP) team: EP-FXT performed a follow-up observation of EP250916a (GCN 41841) at 2025-09-17 11:34:24 (UTC), about 32 hours after the WXT detection, with an exposure time of 3.1 ks. FXT detected a bright source within the WXT error circle at R.A. = 268.2379 and Dec. = –35.3222 (J2000), with a positional uncertainty of 10 arcseconds (radius, 90% confidence level, including both statistical and systematic errors). The fit with a power-law spectrum yields Nh = 3.1 × 10^21 cm^-2 and a photon index of 1.66 ± 0.02, with a 0.5–10 keV flux of 5.4 × 10^-10 erg/s/cm^2. Additionally, we note that this source keeps brightening in the WXT monitoring, with the flux rising from approximately 3 × 10^-11 erg/s/cm^2 at 2025-09-16 03:33:13 to about 2 × 10^-10 erg/s/cm^2 at 2025-09-17 17:54:10 (UTC). Further follow-up observations are encouraged to identify the nature of this source. 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/41861. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39926] GRB 250916A: MAO/AZT-22 optical observations
by GCN Circulars 18 Sep '25

18 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41860 SUBJECT: GRB 250916A: MAO/AZT-22 optical observations DATE: 25/09/18 05:09:34 GMT FROM: Yodgor Rajabov at UBAI <rajabov(a)astrin.uz> O. Burkhonov, Y. Rajabov, B.Abidkhanov, S. Eghamberdiev, Y. Tillayev (UBAI), A. Shaymanov (Maidanak Observatory/UBAI) report on behalf of UBAI team. We observed the field of the GRB 250916A (Fermi GBM team, GCN 41839; Arya et al., GCN 41843; Cheung et al., GCN 41855) with the 1.5-m at Maidanak Observatory telescope AZT-22 equipped with the 4kx4k CCD SNUCAM camera(Im et al., 2010). We obtained series of 300 sec. images in Bessel R filter on September 17, 18:35:18-19:02:20 UTC. The OT (Belkin et al., GCN 41847; Mohan et al., GCN 41858, Moskvitin et al. GCN 41859) is clearly detected in the individual and stacked frames with the brightness of R = 19.76 +/- 0.03 (t_mid - T0 = 1.2229 days = 29.4917 hours). All the data have been reduced by a single data processing pipeline, STDPipe (Karpov et al., 2022). Images obtained in Johnson Cousin filters were calibrated using the Gaia DR3 Synphot catalog. For image template subrtaction we used PanSTARRS DR2 catalog. The data has not corrected for the Galactic extinction. Maidanak astronomical observatory (MAO) is an observational facility of the Ulugh Beg Astronomical Institute (UBAI), Uzbekistan Academy of Sciences (http://maidanak.uz/) View this GCN Circular online at https://gcn.nasa.gov/circulars/41860. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39925] GRB 250916A: SAO RAS optical observations
by GCN Circulars 17 Sep '25

17 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41859 SUBJECT: GRB 250916A: SAO RAS optical observations DATE: 25/09/17 23:24:23 GMT FROM: Alexander Moskvitin at SAO RAS <mosk(a)sao.ru> A. Moskvitin, O. Spiridonova (SAO RAS), A. Pozanenko (IKI), A. Ghosh, S. Razzaque (CAPP, University of Johannesburg), Tao An and Yuanqi Liu (Shanghai Astronomical Observatory) report on behalf of GRB follow-up collaboration and IKI-GRB-FuN. We observed the field of the GRB 250916A (Fermi GBM team, GCN 41839; Arya et al., GCN 41843; Cheung et al., GCN 41855) with the 1-m SAO RAS telescope Zeiss-1000 equipped with CCD-photometer. We obtained series of 300 sec. images in BVRcIc bands on September 17, 20:21:44--21:42:59 UT. The OT (Belkin et al., GCN 41847; Mohan et al., GCN 41858) is clearly detected in the individual and stacked frames with the brightness of R = 19.60 +/- 0.02 (t_mid - T0 = 1.3059 days = 31.3419 hours). Preliminary photometry is based on the nearby objects from PanSTARRS (magnitudes converted with Lupton 2005 equations) and has not corrected for the Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/41859. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39924] GRB 250916A : GIT optical observations
by GCN Circulars 17 Sep '25

17 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41858 SUBJECT: GRB 250916A : GIT optical observations DATE: 25/09/17 21:43:01 GMT FROM: V. Swain at IIT Bombay <vishwajeet.s(a)iitb.ac.in> T. Mohan, V. Swain, A.P. Saikia, V. Bhalerao (IITB), G.C. Anupama, S. Barway (IIA) and R. Norbu (IAO) report on behalf of the GIT team: We observed the field of Fermi GRB 250916A (Fermi GBM team, GCN 41839) with 0.7m GROWTH-India Telescope (GIT) in r' filter. We started the observation at 2025-09-17 17:34:08 UT, i.e., 28.08 hours after the Fermi GBM trigger. The source is detected at the position reported by GOTO (Belkin et al., GCN 41847) and photometry result follows as: | MJD (mid) | tmid-t0 (hours) | Filter | Exposure (s) | Mag (AB) | | ------------- | ----------- | ------ | ------------ | -------------- | | 60935.73411 | 28.13 | r' | 360 | 19.73 +- 0.06 | The source is fading and photometric result is consistent with Belkin et al., GCN 41847. More broadband observations are under way. The measurement is calibrated against PanSTARRS DR1 (Chambers et al., 2016) and not corrected for Galactic extinction. The GROWTH India Telescope (GIT; Kumar et al. 2022) is a 70-cm telescope with a 0.7-degree field of view, set up by the Indian Institute of Astrophysics (IIA) and the Indian Institute of Technology Bombay (IITB) with funding from DST-SERB and IUSSTF. It is located at the Indian Astronomical Observatory (Hanle), operated by IIA. We acknowledge funding by the IITB alumni batch of 1994, which partially supports the operations of the telescope. Telescope technical details are available at https://sites.google.com/view/growthindia/. View this GCN Circular online at https://gcn.nasa.gov/circulars/41858. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39923] LIGO/Virgo/KAGRA S250917aq: Three counterpart neutrino candidates from IceCube neutrino searches
by GCN Circulars 17 Sep '25

17 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41857 SUBJECT: LIGO/Virgo/KAGRA S250917aq: Three counterpart neutrino candidates from IceCube neutrino searches DATE: 25/09/17 21:05:39 GMT FROM: A. Zegarelli at Ruhr University Bochum <azegarelli(a)icecube.wisc.edu> IceCube Collaboration (http://icecube.wisc.edu/) reports: Searches for track-like muon neutrino events detected by IceCube consistent with the sky localization of gravitational-wave candidate S250917aq in a time range of 1000 seconds centered on the alert event time (2025-09-17 13:13:34.401 UTC to 2025-09-17 13:30:14.401 UTC) have been performed [1,2]. During this time period IceCube was collecting good quality data. Two hypothesis tests were conducted. The first search is a maximum likelihood analysis which searches for a generic point-like neutrino source coincident with the given GW skymap. The second uses a Bayesian approach to quantify the joint GW + neutrino event significance, which assumes a binary merger scenario and accounts for known astrophysical priors, such as GW source distance, in the significance estimate [3]. Three track-like events are found in spatial and temporal coincidence with the gravitational-wave candidate S250917aq calculated from the map circulated in the 4-Update notice. This represents an overall p-value of 0.0096 from the generic transient search and an overall p-value of 0.0197 for the Bayesian search. These p-values measure the consistency of the observed track-like events with the known atmospheric backgrounds for this single map (not trials corrected for multiple GW events). The most probable multi-messenger source direction based on the neutrinos and GW skymap is RA 243.72, Dec -34.23 degrees in the generic transient search. The reported p-values can differ due to the estimated distance of the GW candidate. The distance is used as a prior in the Bayesian binary merger search, while it is not taken into account in the generic transient point-like source search. The false alarm rate of these coincidences can be obtained by multiplying the p-values with their corresponding GW trigger rates. Further details are available at https://gcn.nasa.gov/missions/icecube. Additional details and updates will be posted at https://roc.icecube.wisc.edu/public/LvkNuTrackSearch/. Properties of the coincident events are shown below. | dt(s) | RA(deg) | Dec(deg) | Angular uncertainty(deg)| p-value(generic transient)| p-value(Bayesian) | |-------|----------|----------|-------------------------|---------------------------|-----------------------| | -497.79 | 228.08 | -34.97 | 0.43 | 0.0307 | null | | -82.26 | 243.67 | -34.25 | 0.43 | 0.0096 | 0.0809 | | -62.98 | 38.47 | 36.82 | 3.99 | null | 0.0302 | where: dt = Time of track event minus time of GW trigger (sec) Angular uncertainty = Angular uncertainty of track event: the radius of a circle representing 90% CL containment by area. p-value = the p-value for this specific track event from each search. Event p-values are provided when the per-event p-value is less than 0.1 in either search. 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] M. G. Aartsen et al 2020 ApJL 898 L10 [2] Abbasi et al. Astrophys.J. 944 (2023) 1, 80 [3] I. Bartos et al. 2019 Phys. Rev. D 100, 083017 View this GCN Circular online at https://gcn.nasa.gov/circulars/41857. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39922] LIGO/Virgo/KAGRA S250917aq: Updated Sky localization
by GCN Circulars 17 Sep '25

17 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41856 SUBJECT: LIGO/Virgo/KAGRA S250917aq: Updated Sky localization DATE: 25/09/17 19:57:03 GMT FROM: Aditya Vijaykumar <aditya.vijaykumar(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 S250917aq (GCN Circular 41850). 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/S250917aq For the Bilby.multiorder.fits,0 sky map, the 90% credible region is 5216 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 696 +/- 162 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/41856. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39921] GRB 250916A: Glowbug gamma-ray detection
by GCN Circulars 17 Sep '25

17 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41855 SUBJECT: GRB 250916A: Glowbug gamma-ray detection DATE: 25/09/17 19:22:38 GMT FROM: C.C. Cheung at Naval Research Lab <Teddy.Cheung(a)nrl.navy.mil> C.C. Cheung, R. Woolf, M. Kerr, J.E. Grove (NRL), A. Goldstein (USRA), C.A. Wilson-Hodge, D. Kocevski (MSFC), and M.S. Briggs (UAH) report: The Glowbug gamma-ray telescope [1,2,3], operating on the International Space Station, reports the detection of GRB 250916A, which was also detected by Fermi/GBM (GCN 41839), AstroSat/CZTI (GCN 41843), and CALET (Trig ID. 1442064382). Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2025-09-16 13:33:04.840 with a duration of 64.5 s and a total significance of about 110 sigma. The light curve comprises two primary peaks at ~T0+22s and ~T0+44s. A search of the Glowbug data for the earlier, fainter emission reported in GCN 41839 by Fermi/GBM (trigger time 13:29:21) was inconclusive. The analysis results presented here are preliminary and use a response function that lacks a detailed characterization of the surrounding passive structure of the ISS. Glowbug is a NASA-funded technology demonstrator for sensitive, low-cost gamma-ray transient telescopes developed, built, and operated by the U.S. Naval Research Laboratory (NRL) with support from the University of Alabama in Huntsville, USRA, and NASA MSFC. It was launched on 2023 March 15 aboard the Department of Defense Space Test Program’s STP-H9 to the ISS, and operated until 2024 April when it was put in safe storage on orbit. Glowbug was recently removed from storage and resumed operation on 2025 September 12. [1] Grove, J.E. et al. 2020, Proc. Yamada Conf. LXXI, arXiv:2009.11959 [2] Woolf, R.S. et al. 2022, Proc. SPIE, 12181, id. 121811O [3] Woolf, R.S. et al. 2024, Proc. SPIE, 13151, id. 1315108 Distribution Statement A: Approved for public release. Distribution is unlimited. View this GCN Circular online at https://gcn.nasa.gov/circulars/41855. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39920] GRB250917B: WFST optical observations
by GCN Circulars 17 Sep '25

17 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41854 SUBJECT: GRB250917B: WFST optical observations DATE: 25/09/17 19:16:36 GMT FROM: ylhua(a)pmo.ac.cn Yan-Long Hua, Bin Li, Bin-Yang Liu, Tian-Rui Sun, Jin-Jun Geng, Xue-Feng Wu, Zhi-Ping Jin, Wen Zhao, Ji-An Jiang report on behalf of the WFST team: Following the detection of GRB 250917B by Fermi GBM (Fermi GBM Team, GCN 41846) and Swift-BAT (R. Caputo, GCN 41848), we performed follow-up observations using the Wide Field Survey Telescope (WFST Collaboration; arXiv:2306.07590) at the Lenghu Astronomical Observation Base in Qinghai Province, China. Observations were performed in the g/r/i band, starting from 2025-09-17 13:15:02（UTC）to 2025-09-17 13:42:39（UTC）, with an exposure of 120s*3 for each band. The r-band stacked image reaches a limiting magnitude of 22.3 (AB). We performed image subtraction using Pan-STARRS1 (PS1) reference images, but did not find any significant optical counterpart. We also examined the Swift-XRT (J.A. Kennea, GCN 41851) sources within the GRB error region: Source 1 is located near the center of a galaxy, making it difficult to justify an optical counterpart. Source 5 and Source 6 show no detectable optical counterparts in our images. These results suggest that no clear optical afterglow was detected at the positions of the X-ray sources within our observation limits. We thank the WFST staff for supporting these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/41854. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39919] GRB 250916A: Swift ToO observations
by GCN Circulars 17 Sep '25

17 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41853 SUBJECT: GRB 250916A: Swift ToO observations DATE: 25/09/17 19:02:32 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 Fermi/GBM-detected event GRB 250916A. Automated analysis of the XRT data will be presented online at https://www.swift.ac.uk/ToO_GRBs/00021859 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 Fermi/GBM 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/41853. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39918] GRB 250917B: Fermi GBM Observation
by GCN Circulars 17 Sep '25

17 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41852 SUBJECT: GRB 250917B: Fermi GBM Observation DATE: 25/09/17 18:53:07 GMT FROM: Rushikesh Digambar Sonawane PHD231014 at IISER, TVM <rushikesh23(a)iisertvm.ac.in> R. Sonawane (IISER, TVM) and C. Meegan (UAH) report on behalf ofthe Fermi Gamma-ray Burst Monitor Team:"At 06:27:44.33 UT on 17 September 2025, the Fermi Gamma-ray Burst Monitor (GBM)triggered and located GRB 250917B (trigger 779783269/250917269).which was also detected by Swift BAT (R. Caputo et al. 2025, GCN 41848).The Fermi GBM on-ground location is consistent with the Swift BAT position.The angle from the Fermi LAT boresight is 48 degrees.The GBM light curve consists of a single emission episode with a duration (T90)of about 0.2 s (50-300 keV). The time-averaged spectrumfrom T0-0.2 to T0+0.3 s is best fit bya power law function with an exponential high-energy cutoff.The power law index is -1 +/- 0.2 and the cutoff energy,parameterized as Epeak, is 120 +/- 20 keV.The event fluence (10-1000 keV) in this time interval is(3.2 +/- 0.3)E-07 erg/cm^2. The 64-ms peak photon flux measuredstarting from T0+0.0 s in the 10-1000 keV band is 24 +/- 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.htmlFor 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/41852. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39917] GRB 250917B: Swift-XRT observations
by GCN Circulars 17 Sep '25

17 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41851 SUBJECT: GRB 250917B: Swift-XRT observations DATE: 25/09/17 17:14:55 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> J.A. Kennea (PSU), A.P. Beardmore (U. Leicester), J.P. Osborne (U. Leicester), B. Sbarufatti (INAF-OAB), C. Salvaggio (INAF-OAB), M. Ferro (INAF-OAB), D.N. Burrows (PSU), S. Lanava (PSU) and P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team: We have analysed 5.5 ks of Photon Counting (PC) mode XRT data for GRB 250917B, collected between T0+142 s and T0+28.4 ks. Three uncatalogued X-ray sources have been detected within the estimated 3-sigma Swift-BAT error region (296 arcsec), however none of them is above the RASS limit or shows definitive signs of fading. Therefore, at the present time we cannot identify which, if any, is the afterglow. Details of these sources are given below: Source 1: RA (J2000.0): 291.3458 = 19h 25m 23.00s Dec (J2000.0): +11.1151 = +11d 06' 54.5" Error: 5.5 arcsec (radius, 90% conf. [Enhanced position]) Count-rate: (5.5 [+1.3, -1.2])e-3 ct s^-1 Distance: 113 arcsec from Swift-BAT position. Flux: (1.26 [+0.30, -0.28])e-13 erg cm^-2 s^-1 (observed, 0.3-10 keV) Source 5: RA (J2000.0): 291.3929 = 19h 25m 34.30s Dec (J2000.0): +11.0748 = +11d 04' 29.2" Error: 7.7 arcsec (radius, 90% conf.) Count-rate: (4.6 [+5.4, -3.9])e-4 ct s^-1 Distance: 147 arcsec from Swift-BAT position. Source 6: RA (J2000.0): 291.4312 = 19h 25m 43.49s Dec (J2000.0): +11.1014 = +11d 06' 05.0" Error: 8.3 arcsec (radius, 90% conf.) Count-rate: (7.4 [+6.4, -4.8])e-4 ct s^-1 Distance: 192 arcsec from Swift-BAT position. Flux: (1.47 [+1.27, -0.95])e-12 erg cm^-2 s^-1 (observed, 0.3-10 keV) Three uncatalogued sources were also detected too far from the GRB position to be likely afterglow candidates. 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/01350381. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/41851. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39916] LIGO/Virgo/KAGRA S250917aq: Identification of a GW compact binary merger candidate
by GCN Circulars 17 Sep '25

17 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41850 SUBJECT: LIGO/Virgo/KAGRA S250917aq: Identification of a GW compact binary merger candidate DATE: 25/09/17 14:18:25 GMT FROM: daniela.pascucci(a)ugent.be The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report: We identified the compact binary merger candidate S250917aq during real-time processing of data from LIGO Hanford Observatory (H1) and Virgo Observatory (V1) at 2025-09-17 13:21:54.401 UTC (GPS time: 1442150532.401). The candidate was found by the GstLAL [1] analysis pipeline. S250917aq is an event of interest because its false alarm rate, as estimated by the online analysis, is 1.1e-13 Hz, or about one in 1e5 years. The event's properties can be found at this URL: https://gracedb.ligo.org/superevents/S250917aq 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 3%. 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 5646 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 687 +/- 182 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/41850. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39915] Fermi GRB 250917B: Global MASTER-Net observations report
by GCN Circulars 17 Sep '25

17 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41849 SUBJECT: Fermi GRB 250917B: Global MASTER-Net observations report DATE: 25/09/17 12:31:52 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) started inspect of the Fermi GRB 250917B ( Fermi GBM team, GCN 41846) errorbox 21352 sec after notice time and 21386 sec after trigger time at 2025-09-17 12:24:10 UT, with upper limit up to 13.2 mag. Observations started at twilight. The observations began at zenith distance = 22 deg. The sun altitude is -11.2 deg. The galactic latitude b = 19 deg., longitude l = 57 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2993668 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 21416 | 2025-09-17 12:24:10 | MASTER-Tunka | (18h 22m 39.27s , +29d 57m 54.1s) | C | 60 | 13.2 | 21498 | 2025-09-17 12:25:32 | MASTER-Tunka | (18h 19m 56.75s , +28d 02m 47.7s) | C | 60 | 13.0 | 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/41849. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39914] GRB 250917B: Swift detection of a short burst
by GCN Circulars 17 Sep '25

17 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41848 SUBJECT: GRB 250917B: Swift detection of a short burst DATE: 25/09/17 06:48:14 GMT FROM: K.L. Page at U Leicester <klp5(a)leicester.ac.uk> R. Caputo (GSFC), C. Gronwall (PSU) and K. L. Page (U Leicester) report on behalf of the Neil Gehrels Swift Observatory Team: At 06:27:44 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 250917B (trigger=1350381). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 291.378, +11.113 which is RA(J2000) = 19h 25m 31s Dec(J2000) = +11d 06' 48" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a short, single peaked structure with a duration of about 0.5 sec. The peak count rate was ~8000 counts/sec (15-350 keV), at ~0 sec after the trigger. The XRT began observing the field at 06:29:58.5 UT, 134.2 seconds after the BAT trigger. No source was detected in 681 s of promptly downlinked data. We are waiting for the full dataset to detect and localise the XRT counterpart. UVOT took a finding chart exposure of 150 seconds with the White filter starting 138 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 25% of the BAT error circle. The typical 3-sigma upper limit has been about 19.6 mag. The 8'x8' region for the list of sources generated on-board covers 100% of the BAT error circle. The list of sources is typically complete to about 18 mag. No correction has been made for the large, but uncertain, extinction expected. 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/41848. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39913] GRB 250916A: GOTO optical counterpart candidate
by GCN Circulars 17 Sep '25

17 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41847 SUBJECT: GRB 250916A: GOTO optical counterpart candidate DATE: 25/09/17 06:44:08 GMT FROM: Sergey Belkin at Monash University <sergey.belkin(a)monash.edu> S. Belkin, D. O'Neill, B. P. Gompertz, R. Starling, K. Ackley, M. Dyer, J. Lyman, K. Ulaczyk, D. Steeghs, D. Galloway, V. Dhillon, P. O'Brien, G. Ramsay, K. Noysena, R. Kotak, R. Breton, J. Casares, L. Nuttall, B. Godson, T. Killestein, A. Kumar, M. Pursiainen, report on behalf of GOTO collaboration: We report on optical observations with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022, Dyer et al. 2024) in response to GRB 250916A (Fermi GBM team, GCN 41839; Arya et al., GCN 41843). Targeted observations were performed beginning at 2025-09-16 23:39:53 UT (+10.18h post trigger) and continued through to 2025-09-17 04:55:45 UT (+15.44h post trigger). 211 images were taken, across 10 unique pointings, covering 422.1 sq deg within the 90% localisation contour. ~68.1% of the total 2D localisation probability was covered, with an average 5-sigma depth of 20.0 mag. 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. A new optical source, GOTO25hed, is identified within the GBM 90% localisation region with coordinates (J2000) RA = 26.570161, DEC = 36.16543. The source was initially detected with magnitude L = 18.90 ± 0.11 AB mag (+10.43h post trigger), before fading to L = 19.28 ± 0.12 AB mag (+14.47h post trigger). In total, the source was detected 3 times in our observations. The observed decay rate across the 4 hours our observations span is ~t^(-1.05±0.03). ATLAS forced photometry (Shingles et al. 2021) reveals a non-detection down to a 5-sigma upper limit of o > 19.6 AB mag at 2025-09-16 11:50:38 UT (-1.65h before trigger). We find no evidence of the source prior to the GRB trigger time in previous GOTO or ATLAS observations. A summary of our observations is presented below. +-----------------------------------------------------------------------------+ | Observation time (UT) | t-t0 | filter | AB mag | +-----------------------------------------------------------------------------+ | 2025-09-15 05:57:16 | -31.53h | L | >19.00 | | 2025-09-16 23:55:24 | +10.43h | L | 18.90 ± 0.11 | | 2025-09-17 02:49:13 | +13.33h | L | 19.17 ± 0.07 | | 2025-09-17 03:57:43 | +14.47h | L | 19.28 ± 0.12 | +-----------------------------------------------------------------------------+ 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/41847. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39912] GRB 250917B: Fermi GBM Final Real-time Localization
by GCN Circulars 17 Sep '25

17 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41846 SUBJECT: GRB 250917B: Fermi GBM Final Real-time Localization DATE: 25/09/17 06:38:07 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 06:27:44 UT on 17 Sep 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250917B (trigger 779783269.329994 / 250917269). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 275.0, Dec = 29.0 (J2000 degrees, equivalent to J2000 18h 19m, 29d 00'), with a statistical uncertainty of 6.2 degrees. The angle from the Fermi LAT boresight is 25.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250917269/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250917269/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250917269/… View this GCN Circular online at https://gcn.nasa.gov/circulars/41846. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39911] GRB 250917A: Fermi GBM Final Real-time Localization
by GCN Circulars 17 Sep '25

17 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41845 SUBJECT: GRB 250917A: Fermi GBM Final Real-time Localization DATE: 25/09/17 02:23:49 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 02:13:13 UT on 17 Sep 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250917A (trigger 779767998.991126 / 250917093). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 14.5, Dec = -44.6 (J2000 degrees, equivalent to J2000 00h 58m, -44d 36'), with a statistical uncertainty of 21.8 degrees. The angle from the Fermi LAT boresight is 28.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250917093/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250917093/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250917093/… View this GCN Circular online at https://gcn.nasa.gov/circulars/41845. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39910] The EP-WXT trigger 01709241037 is likely a flaring star
by GCN Circulars 17 Sep '25

17 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41844 SUBJECT: The EP-WXT trigger 01709241037 is likely a flaring star DATE: 25/09/17 02:17:05 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> B.T. Wang (YNAO, CAS), S. Q . Jiang, W. D. Zhang (NAO, CAS) on behalf of the Einstein Probe (EP) team: The EP-WXT trigger 01709241037 at the time of 2025-09-16T23:34:38 (UTC), is likely a stellar flare associated with UPM J0113-5939. The estimated flux of the flare is around 6e-11 erg/s/cm^2 in 0.5-4.0 keV, corresponding to an X-ray luminosity of around 1.3e31 erg/s. 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/41844. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39909] GRB 250916A: AstroSat CZTI detection of a bright long burst
by GCN Circulars 16 Sep '25

16 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41843 SUBJECT: GRB 250916A: AstroSat CZTI detection of a bright long burst DATE: 25/09/16 18:23:31 GMT FROM: Anuraag Arya at IIT Bombay <aryaanuraag910(a)gmail.com> A. Arya (IITB), A. Goyal (IITB), M. Tembhurnikar (IUCAA), Harsha K. H. (IUCAA), S. Salunke (IUCAA), G. Waratkar (Caltech/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 bright long-duration GRB 250916A which was also detected by Fermi GBM (Fermi GBM Team, GCN Circ. 41839), and CALET (Trig ID. 1442064382). Note that we detected the bright burst roughly 250 s after the initial fainter spike as seen in the GBM lightcurve. The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2025-09-16 13:33:28.50 UTC. The measured peak count rate associated with the burst is 79 (+29, -4) counts/s above the background in the combined data of two quadrants (out of four), with a total of 1695 (+232, -241) counts. We caution that there is a 0.3 s readout dead time in CZT data during the burst which affects the calculated total counts. The local mean background count rate was 135 (+1, -2) counts/s. Using cumulative rates, we measure a T90 of 48 (+2, -6) s. The source was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2025-09-16 13:33:26.00 UTC. The measured peak count rate associated with the burst is 556 (+80, -24) counts/s above the background in the combined data of all quadrants, with a total of 13048 (+742, -896) counts. The local mean background count rate was 1180 (+5, -4) counts/s. We measure a T90 of 50 (+2, -5) 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/41843. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39908] GRB 250910A: SVOM/ECLAIRs refined analysis
by GCN Circulars 16 Sep '25

16 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41842 SUBJECT: GRB 250910A: SVOM/ECLAIRs refined analysis DATE: 25/09/16 16:03:05 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Baptiste Hubert, Nicolas Dagoneau, Stéphane Schanne (CEA), Jean-Luc Atteia (IRAP), Frédéric Piron (LUPM), Yinuo Ma, Donghua Zhao, Wenjin Xie (NAOC) Using the event-by-event data downloaded through the X-band ground station, we report further analysis of ECLAIRs observations of GRB 250910A (SVOM burst-id sb25091001). The burst that triggered ECLAIRs (GCN 41769) consists of a broad structure with a duration of T90 = 22 -2/+3 s in the 4-20 keV energy band. The time-averaged spectrum from T0-15.5 s to T0+6.7 s (T0 = 2025-09-10T03:16:30) in the energy range 4-120 keV is best fitted by a power-law model with photon index 1.7 +/-0.2. With this model, the 4-120 keV flux is (2.2 -0.4/+0.2)e-08 erg/cm^2/s. All the quoted errors are at the 68% confidence level. 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. ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC. The SVOM/ECLAIRs point of contact for this burst is: Nicolas Dagoneau (CEA) (nicolas.dagoneau at cea.fr) View this GCN Circular online at https://gcn.nasa.gov/circulars/41842. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39907] EP250916a: Einstein Probe detection of an X-ray transient
by GCN Circulars 16 Sep '25

16 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41841 SUBJECT: EP250916a: Einstein Probe detection of an X-ray transient DATE: 25/09/16 16:02:54 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Q. Y. Wu (NAO, CAS), C. Y. Dai (NJU), D. Y. Li, H. W. Pan (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 through ground data analysis, designated EP250916a. The WXT position of the source is R.A. = 268.279 deg, DEC = -35.317 deg (J2000) with an uncertainty of 2.4 arcmin in radius (90% C.L. statistical and systematic), located at low Galactic latitude (l = 355.331, b = -4.634). The source was detected in three consecutive observations: the first started at 2025-09-16T03:33:13 (UTC) with a flux of ~3e-11 erg/s/cm^2; two subsequent observations, approximately 2 h and 6 h later, also detected the source with slightly higher fluxes of ~5e-11 erg/s/cm^2. As of the latest observation, the transient has persisted for ~7 hours. A preliminary spectral analysis shows that the 0.5-4 keV spectrum can be fitted by an absorbed power-law model with Galactic hydrogen column density fixed at 3.76 x 10^21 cm^-2 and a photon index of 1.1 (-/+0.8). No known X-ray sources have been found previously within the EP-WXT error circle. A stellar flare origin cannot be excluded at this stage. Follow-up observations with the Follow-up X-ray Telescope (FXT) on board EP have been scheduled, and further information will be updated when the telemetry data are 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/41841. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39906] Fermi GRB 250916A: Global MASTER-Net observations report
by GCN Circulars 16 Sep '25

16 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41840 SUBJECT: Fermi GRB 250916A: Global MASTER-Net observations report DATE: 25/09/16 15:30:58 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) started inspect of the Fermi GRB 250916A ( Fermi GBM team, GCN 41839) errorbox 2134 sec after notice time and 2165 sec after trigger time at 2025-09-16 14:05:26 UT, with upper limit up to 20.8 mag. The observations began at zenith distance = 44 deg. The sun altitude is -24.7 deg. The galactic latitude b = -20 deg., longitude l = 137 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2992979 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 2196 | 2025-09-16 14:05:26 | MASTER-Tunka | (01h 01m 35.41s , +42d 32m 50.5s) | C | 60 | 20.7 | 2196 | 2025-09-16 14:05:26 | MASTER- | (01h 02m 07.93s , +42d 25m 57.0s) | C | 60 | 20.5 | 2271 | 2025-09-16 14:06:42 | MASTER-Tunka | (01h 31m 07.38s , +48d 15m 08.4s) | C | 60 | 19.6 | 2271 | 2025-09-16 14:06:42 | MASTER- | (01h 31m 43.29s , +48d 08m 17.2s) | C | 60 | 19.5 | 2825 | 2025-09-16 14:15:56 | MASTER-Tunka | (01h 01m 37.13s , +42d 32m 44.7s) | C | 60 | 20.6 | 2825 | 2025-09-16 14:15:56 | MASTER- | (01h 02m 10.56s , +42d 25m 34.6s) | C | 60 | 20.6 | 2900 | 2025-09-16 14:17:11 | MASTER-Tunka | (01h 31m 06.83s , +48d 15m 06.1s) | C | 60 | 20.2 | 2900 | 2025-09-16 14:17:11 | MASTER- | (01h 31m 43.65s , +48d 07m 58.6s) | C | 60 | 19.8 | 4244 | 2025-09-16 14:39:34 | MASTER-Tunka | (01h 17m 38.67s , +38d 43m 55.2s) | C | 60 | 19.8 | 4244 | 2025-09-16 14:39:34 | MASTER- | (01h 18m 09.42s , +38d 37m 35.4s) | C | 60 | 19.7 | 4985 | 2025-09-16 14:51:56 | MASTER-Tunka | (01h 01m 35.37s , +42d 30m 26.2s) | C | 60 | 20.7 | 4985 | 2025-09-16 14:51:56 | MASTER- | (01h 02m 11.14s , +42d 22m 49.2s) | C | 60 | 20.6 | 5059 | 2025-09-16 14:53:10 | MASTER-Tunka | (01h 31m 07.69s , +48d 15m 07.8s) | C | 60 | 20.2 | 5059 | 2025-09-16 14:53:10 | MASTER- | (01h 31m 47.54s , +48d 07m 33.5s) | C | 60 | 19.9 | 5553 | 2025-09-16 15:01:23 | MASTER-Tunka | (01h 17m 43.01s , +38d 42m 15.8s) | C | 60 | 19.8 | 5553 | 2025-09-16 15:01:23 | MASTER- | (01h 18m 15.41s , +38d 35m 49.9s) | C | 60 | 19.7 | 5775 | 2025-09-16 15:05:05 | MASTER-Tunka | (01h 01m 31.47s , +42d 30m 13.1s) | C | 60 | 20.8 | 5775 | 2025-09-16 15:05:06 | MASTER- | (01h 02m 08.39s , +42d 23m 51.2s) | C | 60 | 20.6 | 5852 | 2025-09-16 15:06:22 | MASTER-Tunka | (01h 31m 05.98s , +48d 12m 03.1s) | C | 60 | 20.3 | 5852 | 2025-09-16 15:06:22 | MASTER- | (01h 31m 46.96s , +48d 05m 44.0s) | C | 60 | 19.9 | 6285 | 2025-09-16 15:13:36 | MASTER-Tunka | (01h 17m 33.49s , +38d 39m 54.6s) | C | 60 | 19.9 | 6285 | 2025-09-16 15:13:36 | MASTER- | (01h 18m 04.22s , +38d 34m 21.2s) | C | 60 | 19.7 | 6508 | 2025-09-16 15:17:18 | MASTER-Tunka | (01h 01m 28.89s , +42d 27m 40.0s) | C | 60 | 20.7 | 6508 | 2025-09-16 15:17:18 | MASTER- | (01h 02m 05.60s , +42d 21m 48.9s) | C | 60 | 20.7 | 6582 | 2025-09-16 15:18:33 | MASTER-Tunka | (01h 31m 05.87s , +48d 12m 44.6s) | C | 60 | 19.7 | 6582 | 2025-09-16 15:18:33 | MASTER- | (01h 31m 46.70s , +48d 06m 57.1s) | C | 60 | 19.6 | 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/41840. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39905] GRB 250916A: Fermi GBM Final Real-time Localization
by GCN Circulars 16 Sep '25

16 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41839 SUBJECT: GRB 250916A: Fermi GBM Final Real-time Localization DATE: 25/09/16 13:40:16 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 13:29:21 UT on 16 Sep 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250916A (trigger 779722166.007904 / 250916562). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 29.3, Dec = 40.3 (J2000 degrees, equivalent to J2000 01h 57m, 40d 17'), with a statistical uncertainty of 9.8 degrees. The angle from the Fermi LAT boresight is 66.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250916562/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250916562/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250916562/… View this GCN Circular online at https://gcn.nasa.gov/circulars/41839. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39904] EP250827b: VLA Observations
by GCN Circulars 16 Sep '25

16 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41838 SUBJECT: EP250827b: VLA Observations DATE: 25/09/16 13:27:15 GMT FROM: Genevieve Schroeder at Cornell University <genevieveschroeder(a)u.northwestern.edu> G. Schroeder (Cornell), D. A. Perley (LJMU), X. J. Hall (CMU), A. Y. Q. Ho (Cornell), Gokul Srinivasaragavan (UMD) report: We observed the location of the optical transient AT2025wkm, associated with EP250827b (Schroeder et al., GCN 41635) with the NSF’s Karl G. Jansky Very Large Array under program 25B-363 (PI Perley) on 2025 September 13 at a mid time of 13:02 UT (~17.3 days post discovery) at a mid frequency of 10 GHz (4 GHz bandwidth). Based on preliminary analysis, we detect a ~6 sigma source with a flux density of ~28 microJy. At a redshift of z = 0.120 (Sevilla et al., GCN 41639), this corresponds to a luminosity of ~1e28 erg/s/Hz. This is a factor of ~6 less luminous than the radio emission associated with SN1998bw (Kulkarni et al. Nature, 395, 663), and a factor of ~5 more luminous than the radio emission associated with SN2006aj (Soderberg et al. 2006, Nature, 442, 1014) at a similar observing frequency and epoch. If the radio emission can be attributed solely to star formation, this would indicate a radio star formation rate of ~3 Msol/year. Additional followup is planned to determine variability of the source. We thank the VLA staff for quickly approving and executing these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/41838. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39903] LIGO/Virgo/KAGRA S250818k: HCT optical follow-up
by GCN Circulars 16 Sep '25

16 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41837 SUBJECT: LIGO/Virgo/KAGRA S250818k: HCT optical follow-up DATE: 25/09/16 08:43:46 GMT FROM: V. Swain at IIT Bombay <vishwajeet.s(a)iitb.ac.in> V. Swain (IITB), G. C. Anupama (IIA), D.K. Sahu (IIA), S. Barway (IIA), H. Das (IIA), J. Basu (IIA), S. Chamoli (IIA), S. P. Singh (IAO), A. Tiwari (IAO), T. Mohan (IITB), A.P. Saikia (IITB), V. Bhalerao (IITB): We observed the optical transient AT2025ulz (Stein et. al, GCN #41414) in the localization region of a candidate binary neutron star merger S250818k (LVK, GCN #41437) using the 2.0m Himalayan Chandra Telescope (HCT) of the Indian Astronomical Observatory (IAO). We obtained single exposure in the SDSS r' filter starting at 2025-09-11T16:04:33.16 UT (~24.61 days post trigger). Image subtraction was performed using a reference frame from CFHT/MegaCam, and the transient was detected in the resulting difference image. The derived photometry is reported below: | JD (mid) | Filter | Exposure (s) | Mag (AB) | Limiting Mag (AB) | | -------------- | ------ | ------------ | ------------ | ----------------- | | 2460930.169828 | r' | 600 | 20.82 ± 0.11 | 21.9 | The magnitudes are calibrated against PanSTARRS DR1 (Chambers et al., 2016) and not corrected for Galactic extinction. Our result is consistent with the photometry followed by (Busmann et. al, GCN #41421; Hall et. al, GCN #41433; Karambelkar et. al, GCN #41436; Nicholl et. al, GCN #41439; Srivastav et. al, GCN #41451; O’Connor et. al, GCN #41452; Gillanders et. al, GCN #41454; Mo et. al, GCN #41456; Liu et. al, GCN #41461; Ackley et. al, GCN #41468; Klose et. al, GCN #41474; Banerjee et. al, GCN #41476; Perley et. al, GCN #41480; D'Avanzo et. al, GCN #41489; Malesani et. al, GCN #41492; Smartt et. al, GCN #41493; Santos et. al, GCN #41501; Becerra et. al, GCN #41502; An et. al, GCN #41503; Passaleva et. al, GCN #41504; Taguchi et. al, GCN #41505; Troja et. al, GCN #41506; Freeburn et. al, GCN #41507; Angulo et. al, GCN #41518; Antier et. al, GCN #41519; Banerjee et. al, GCN #41532; Lipunov et. al, GCN #41534; Busmann et. al, GCN #41535; Kasliwal et. al, GCN #41538; Gillanders et. al, GCN #41540; Becerra et. al, GCN #41544; Pankov et. al, GCN #41548). Further observations are planned. These observations were carried out under the ToO program HCT-2025-C3-P43. We thank the HCT staff for their support during the observations. The Indian Astronomical Observatory is operated by the Indian Institute of Astrophysics, Bengaluru, India. View this GCN Circular online at https://gcn.nasa.gov/circulars/41837. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39902] SVOM/sb25091517: Confirmation of a stellar flare by SVOM/VT
by GCN Circulars 16 Sep '25

16 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41836 SUBJECT: SVOM/sb25091517: Confirmation of a stellar flare by SVOM/VT DATE: 25/09/16 07:10:53 GMT FROM: Huali Li at at NAOC, SVOM <lhl(a)nao.cas.cn> H.L. Li (NAOC), L.P. Xin, Y. N. Ma, Y.L. Qiu, C. Wu, Z.H. Yao, X.H. Han, J. Wang, W.J. Xie, Y. Xu, H.B. Cai, J.Y. Wei (NAOC), J. Palmerio (CEA), Y. Julakanti, R. A. J. Eyles-Ferris (U. Leicester) report on behalf of the SVOM team. SVOM performed an automatic slew on the soft burst triggered by SVOM/ECLAIRs (Julakanti et al., GCN 41834) in VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. The observation with good image quality began at 2025-09-15T22:09:18, i.e., 457 sec post trigger. With X band downlinked data, preliminary analysis shows that the M2 dwarf 1RXS J020013.6-084106 located within MXT's errorbox (Julakanti et al., GCN 41834) was decreasing in brightness from 10.6 mag to 12.2 mag in VT_B during 3 hour time interval after the trigger time. This result confirms that the trigger was due to a stellar flare, as already reported by Jelinek et al. (GCN 41617). Our photometry was estimated in AB magnitude. 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/41836. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39901] SVOM/sb25091517: FRAM-ORM stellar flare - transient observation
by GCN Circulars 16 Sep '25

16 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41835 SUBJECT: SVOM/sb25091517: FRAM-ORM stellar flare - transient observation DATE: 25/09/16 01:34:05 GMT FROM: Martin Jelinek at Astro.Inst-AVCR,Ondrejov <martin.jelinek(a)asu.cas.cz> Martin Jelinek, Jan Strobl (ASU CAS Ondrejov, CZ), Sergey Karpov, Martin Masek, Petr Janecek, Jakub Jurysek, Jan Ebr, Ronan Cunniffe, Petr Travnicek and Michael Prouza (Institute of Physics, Prague, CZ) report: The 25cm robotic telescope FRAM-ORM at La Palma (Spain) reacted robotically to the alert of SVOM/sb25091517 (Julakanti et al. GCN 41834), obtaining a series of 70 x 60s unfiltered images starting at 22:51 UT, i.e. 50 min post trigger. We clearly detect the high proper motion star 1RXS J020013.6-084106 at coordinates R.A. = 02:00:12.98, Dec. = -08:40:53.5 (J2000), located 18 arcsec from the MXT position as noted in the discovery circular. The star shows a decay from unfiltered magnitude ~11.0 to ~11.4 over our 80-minute observing sequence ending at 00:11 UT, with one brief 0.1 mag rebrightening episode during the observations. The observed photometric behavior is consistent with the stellar flaring nature suggested in the discovery circular. View this GCN Circular online at https://gcn.nasa.gov/circulars/41835. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39900] SVOM/sb25091517: SVOM detection of an X-ray transient
by GCN Circulars 15 Sep '25

15 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41834 SUBJECT: SVOM/sb25091517: SVOM detection of an X-ray transient DATE: 25/09/15 23:23:46 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Y. Julakanti, R. A. J. Eyles-Ferris (U. Leicester), S. Schanne (CEA/Irfu), F. Piron (LUPM), H. Goto (Kanazawa Univ./CEA), report on behalf of the SVOM mission team: At 2025-09-15T22:01:41 UTC (T0), SVOM/ECLAIRs triggered and located the X-ray transient SVOM/sb25091517 (SVOM burst-id). 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 3 alerts. IMT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 8.81 in the [5-20] keV energy band over a time window of 655.36 seconds starting at 2025-09-15T21:56:13 (Tb). The localization of the best alert is R.A., Dec. 30.1388, -8.7614 degrees (J2000) with a 90% confidence level (C.L.) radius of 8.96 arcmin (including systematic error of 2 arcmin added in quadrature). We notice the presence of the known X-ray sources 6dFGS gJ020039.1-084555, 2E 0157.9-0853, 1RXS J020013.6-084106, CXOMP J020012.1-085113 in the ECLAIRs error box. SVOM slewed to the burst. SVOM/MXT began observing the field at 2025-09-15T22:09:15 UTC, 454 seconds after T0. Using onboard processed data we found an X-ray source located at R.A., Dec. 30.0581, -8.6826 degrees: R.A. (J2000) = 2h00m13.94s Dec. (J2000) = -8d40m57.37s with a 90% C.L. radius of 30 arcseconds. This location is 6.73 arcminutes from the ECLAIRs onboard position. This position may be improved as more data is received. We notice that the High Proper Motion Star 1RXS J020013.6-084106 is located at 18 arcsec from the MXT position. Therefore this trigger is likely caused by a flare from this star. 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 Yashaswi Julakanti: skyj1(a)leicester.ac.uk. Please contact the BA by email if you require additional information. View this GCN Circular online at https://gcn.nasa.gov/circulars/41834. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39899] GRB 250912A: Swift/BAT-GUANO localization skymap of a possibly short burst
by GCN Circulars 15 Sep '25

15 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41833 SUBJECT: GRB 250912A: Swift/BAT-GUANO localization skymap of a possibly short burst DATE: 25/09/15 21:59:44 GMT FROM: Jimmy DeLaunay at Penn State <delauj2(a)gmail.com> James DeLaunay (PSU), Samuele Ronchini (PSU), Aaron Tohuvavohu (Caltech), Jamie A. Kennea (PSU), Tyler Parsotan (NASA GSFC), Maia Williams (PSU) report: Swift/BAT did not localize GRB 250912A onboard (T0: 2025-09-12T21:06:23.64 UTC, SVOM trig sb25091206, Fermi Trig 779403988) The Fermi notice, distributed in near real-time, triggered the Swift Mission Operations Center operated Gamma-ray Urgent Archiver for Novel Opportunities (GUANO; Tohuvavohu et al. 2020, ApJ, 900, 1). Upon trigger by this notice, GUANO sent a command to the Swift Burst Alert Telescope (BAT) to save 200 seconds of BAT event-mode data from [-50,+150] seconds around the time of the burst. All the requested event mode data was delivered to the ground. The BAT likelihood search, NITRATES (DeLaunay + Tohuvavohu 2022, ApJ, 941, 169), performed on the temporal window [T0-20 s, T0+20 s], detects the burst with a sqrt(TS) of 10.2 in a 0.512 s analysis time bin, starting at T0 - 0.128 s. Using the NITRATES analysis, parameter estimation was performed to obtain the localization of this burst in the form of a HEALPIX Multi-Order Coverage (MOC) skymap. This localization accounts for both statistical and systematic errors. More details in the creation and calibration of these maps will soon be published (DeLaunay et al. 2025. in prep) The 90% credible area is 13,292 deg2 and the 50% credible area is 4,915 deg2. The integrated probability inside the coded field of view is <1%. The NITRATES skymap is consistent with the SVOM/ECLAIRS position (GCN 41820) and Fermi localization (GCN 41819), and the afterglow position (SVOM/MXT GCN 41820, Swift/XRT GCN 41831, VLT GCN 41829, VLT/HAWK-I GCN 41830). A plot of the probability skymap can be viewed here: [skymap_plot](https://guano.swift.psu.edu/trigger_report?id=779404019/#:~:te… The probability skymap file can be downloaded from the link here [skymap_fits_file](https://guano.swift.psu.edu/files/779404019/0_n_PROBMAP) Instructions on how to read and manipulate this map can be found here: https://guano.swift.psu.edu/documentation More details about this burst can be found on the trigger report page here: https://guano.swift.psu.edu/trigger_report?id=779404019 GUANO is a fully autonomous, extremely low latency, spacecraft commanding pipeline designed for targeted recovery of BAT event mode data around the times of compelling astrophysical events to enable more sensitive GRB searches. A live reporting of Swift/BAT event data recovered by GUANO can be found at: https://www.swift.psu.edu/guano/ View this GCN Circular online at https://gcn.nasa.gov/circulars/41833. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39898] GRB 250912A: SVOM/COLIBRÍ (FM-GFT) optical observations
by GCN Circulars 14 Sep '25

14 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41832 SUBJECT: GRB 250912A: SVOM/COLIBRÍ (FM-GFT) optical observations DATE: 25/09/14 15:36:39 GMT FROM: Alan Watson at UNAM <alan(a)astro.unam.mx> Alan M. Watson (UNAM), Sarah Antier (OCA), Damien Dornic (CPPM), Benjamin Schneider (LAM), Rosa L. Becerra (U Roma), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Nathaniel R. Butler (ASU), Jean-Grégoire Ducoin (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), N. A. Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), and Antonio de Ugarte Postigo (LAM) report: We imaged the field of the SVOM/Fermi GRB 250912A (Ducoin et al., GCN Circ. 41820, and Fermi GBM Team, GCN Circ. 41819) using the DDRAGO two-channel wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope. We observed from 2025-09-13 05:51 to 08:33 UTC (from 8.75 to 11.45 hours after the ECLAIRs trigger) and obtained 112 minutes of simultaneous exposure in the r and z filters and then again from 2025-09-14 05:52 to 08:10 UTC (from 32.78 to 35.07 hours after the ECLAIRs trigger) and obtained 96 minutes of simultaneous exposure in the r and z filters. 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 do not detect the J-band source reported by Garnichey et al. (GCN Circ. 41929) and Ricci et al. (GCN Circ. 41830) to 3-sigma limits at our first epoch of: r > 24.8 z > 23.7 and at our second epoch of: r > 24.7 z > 23.5 This confirms the absence of a similarly bright optical counterpart to the J-band source and confirms its extremely red colors. We have subtracted our two epochs and in the difference image find no clear evidence for an optical transient in the MXT error region (Ducoin et al., GCN Circ. 41820) at our first epoch to 5-sigma limits of: r > 23.9 z > 22.8 Our result is in agreement with earlier observations reported by Lipunov et al. (GCN Circ 41822), Wu et al. (GCN Circ. 41824), and Li et al. (GCN Circ. 41825). Evans et al. (GCN Circ. 41831) report the discovery of an uncataloged X-ray source outside of the MXT error region. This source is close to a galaxy (object 121410150406866805 in the Pan-STARRS DR2 catalog) with r ≈ 19.6 and z ≈ 18.9. At this position in our difference image, we do not see an obvious optical transient, but our ability to quantify this is limited by significant subtraction artifacts. 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/41832. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39897] GRB 250912A: Swift-XRT observations
by GCN Circulars 14 Sep '25

14 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41831 SUBJECT: GRB 250912A: Swift-XRT observations DATE: 25/09/14 14:45:17 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 GRB 250912A (Ducoin et al., GCN 41820; Wang et al., GCN 41826; see also Fermi GBM team, GCN 41819), collecting 2.2 ks of Photon Counting (PC) mode data between T0+11 ks and T0+55 ks after the trigger. We have detected 1 source. This has been automatically classified as an uncatalogued X-ray source. Uncatalogued X-ray sources -------------------------- Source 1 (SWIFT J010009.7+111047): ================================== RA (J2000.0): 15.0405 = 01 00 09.72 Dec (J2000.0): +11.1797 = +11 10 46.9 Error: 7.3 (arcsec, radius, 90% confidence). Detect flag: GOOD Distance: 6.8 arcmin from the SVOM/ECLAIRs position. Mean rate: (3.6 [+2.0, -1.5])e-3 ct s^-1 Mean flux: (2.7 [+1.5, -1.1])e-13 erg cm^-2 s^-1 Peak rate: (3.6 [+2.0, -1.5])e-3 ct s^-1 Peak flux: (2.7 [+1.5, -1.1])e-13 erg cm^-2 s^-1 ECF: 7.43e-11 erg cm^-2 ct^-1 assuming NH=5.11e+20 cm^-2, gamma=0.69 determined from a spectral fit. RASS UL: 7.3e-02 ct s^-1 (converted to XRT; 0.3-10 keV) so the source is not above this 3-sigma upper limit. 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. We note that source 1 lies outside the MXT error region reported by Ducoin et al. (GCN 41820), so it is likely unrelated with the GRB. 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_FIELD00037. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/41831. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39896] GRB250912A: VLT/HAWK-I follow-up observations
by GCN Circulars 14 Sep '25

14 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41830 SUBJECT: GRB250912A: VLT/HAWK-I follow-up observations DATE: 25/09/14 12:29:31 GMT FROM: Roberto Ricci at INAF-IRA <ricci(a)ira.inaf.it> R. Ricci (U Rome), E. Troja (U Rome), M. Yadav (U Rome) and Y. Yang (U. Rome) report: We observed the field of GRB250912A discovered by Fermi/GBM (Fermi GBM team GCN 41819) and SVOM (Ducoin et al. GCN 41820) and classified as a possible short GRB with extended emission (Wang et al. GCN 41826) using the VLT UT4 (Yepun) telescope equipped with the HAWK-I near-infrared imager. Our observations were centered on the SVOM/MXT position (Ducoin et al. GCN 41820) and were carried out in the J filter for a net exposure time of 15 minutes starting on Sep 14th 03:58 UT (31 hours after the trigger). The source reported by Malesani et al. (GCN 41829) and located at coordinates (J2000): RA = 00:59:44.39 Dec = +11:10:07.0 is detected in our imaging with J ~ 22.20 AB mag, thus not showing significant variability since the previous night. No other obvious counterpart is evident in our observations. Further observations are planned. We thank the VLT Observatory staff for promptly executing the observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/41830. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39895] GRB 250912A: VLT observations
by GCN Circulars 14 Sep '25

14 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41829 SUBJECT: GRB 250912A: VLT observations DATE: 25/09/14 10:06:40 GMT FROM: Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani(a)nbi.ku.dk> M. Garnichey (LUX-Paris Obs.), G. Corcoran (UCD), B. Schneider (LAM), L. Izzo (INAF/OACN), A. Saccardi (CEA/Irfu), V. D’Elia (ASI/SSDC), N. Habeeb (Leicester), D. B. Malesani (DAWN/NBI and Radboud), A. Martin-Carrillo (UCD), A. L. Thakur (INAF/IAPS), N. R. Tanvir (Leicester), S. D. Vergani (LUX-Paris Obs.), report on behalf of the Stargate collaboration: Following the reports of deep optical upper limits (Wu et al., GCN 41824; Li et al., GCN 41825), we observed the location of the SVOM GRB 250912A (Ducoin et al., GCN 41820; Wang et al., GCN 41826; see also Smith & Meegan, GCN 41828) using the ESO VLT UT4 (Yepun) equipped with the HAWK-I near-infrared imager. A total of 15 min exposure was secured in the J band, at a mean epoch 2025 Sep 13.130 UT (6.02 hr after the trigger). Image subtraction against archival UKIDSS J-band data reveals no new sources down to the depth of this survey, J ~ 20.6 (AB). As our HAWK-I stack reaches much deeper (limiting magnitude J = 23.9 AB), a more effective search can be carried out by comparison with the Legacy Survey, which is much more sensitive than UKIDSS, but only covers bands different than J. Within the MXT error circle (Ducoin et al., GCN 41820), many objects are visible in our J-band image that are not present in the Legacy Survey. The brightest one has a magnitude J = 22.15 +/- 0.06 (AB), and is located at coordinates (J2000): RA = 00:59:44.39 Dec = +11:10:07.0 For this object, we measure an upper limit z > 23.7 AB in the Legacy Survey, indicating either a remarkably red object or a transient/variable source. Based on the available information, we cannot discriminate between these two possibilities at the moment. Follow-up observations of this source were secured using the ESO VLT UT1 (Antu) equipped with the FORS2 spectrograph. A 3x1000 s spectrum was obtained with the 600z grism (wavelength range 7500 - 10100 AA). No object is detected in the acquisition image (mid time 9.83 hr after trigger) down to a depth of z > 22.7 AB, but a very faint trace is detected in the red part down to ~8550 AA. The very low S/N prevents us from identifying any features, but the continuum detection allows us to set a redshift upper limit z <~ 6. At the present time, no clear afterglow candidate emerges from our observations. A second, deep J-band image is required in order to conclusively identify any faint, variable sources. We acknowledge expert support from the ESO observing staff in Paranal, in particular Robert De Rosa, Juan Carlos Olivares, Jonathan Smoker, Hannah Osborne, and Sam Kim. View this GCN Circular online at https://gcn.nasa.gov/circulars/41829. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39894] GRB 250912A: Fermi GBM Observation
by GCN Circulars 14 Sep '25

14 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41828 SUBJECT: GRB 250912A: Fermi GBM Observation DATE: 25/09/14 00:30:11 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 21:06:23.64 UT on 12 September 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250912A (trigger 779403988/250912879), which was also detected by SVOM/ECLAIRs (Jean-Grégoire Ducoin et al. 2025, GCN 41820). The Fermi GBM on-ground location is consistent with the SVOM/ECLAIRs position. The angle from the Fermi LAT boresight is 49 degrees. The GBM light curve consists of multiple emission episodes with a duration (T90) of about 15 s (50-300 keV). The time-averaged spectrum from T0 to T0+15.6 s is best fit by a simple power law function with index -1.31 +/- 0.04. A power law function with an exponential high-energy cutoff fits the spectrum equally well with a with power law index = -1.05 +/- 0.12 and Epeak = 783 +/- 359. The event fluence (10-1000 keV) in this time interval is (3.1 +/- 0.1)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0-0.26 s in the 10-1000 keV band is 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/41828. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39893] GRB 250911A: Insight-HXMT detection
by GCN Circulars 13 Sep '25

13 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41827 SUBJECT: GRB 250911A: Insight-HXMT detection DATE: 25/09/13 18:17:46 GMT FROM: Chenwei Wang at IHEP <cwwang(a)ihep.ac.cn> Chen-Wei Wang, Jin-Peng Zhang, Shao-Lin Xiong, and Chao Zheng report on behalf of the Insight-HXMT team: At 2025-09-11T01:29:28.250 (T0), Insight-HXMT/HE detected the burst GRB 250911A, which is also detected by Swift/BAT (Palmer et al., GCN 41781) and GECAM-B (Zhang et al., GCN#41813. The Insight-HXMT/HE light curve mainly consists of multi-pulses with a T90 of 24.5 +2.5/-1.5 s. The 1s peak rate, measured from T0+5.250 s, is 1857 cnts/sec. The total counts from this burst is 11720 counts. The HXMT/HE light curve can be found here: https://www.bursthub.cn//admin/static/hxmtgrb250911A.png All measurements above are made with the CsI detectors operating in the regular mode with the energy range of about 60-900 keV (deposited energy). Only gamma-rays with energy greater than about 200 keV can penetrate the spacecraft and leave signals in the CsI detectors installed inside of the telescope. Insight-HXMT is the first Chinese space X-ray telescope, which was funded jointly by the China National Space Administration (CNSA) and the Chinese Academy of Sciences (CAS). More information about it could be found at: http://www.hxmt.org. View this GCN Circular online at https://gcn.nasa.gov/circulars/41827. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39892] GRB 250912A: SVOM/GRM analysis suggests a possible short GRB with extended emission
by GCN Circulars 13 Sep '25

13 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41826 SUBJECT: GRB 250912A: SVOM/GRM analysis suggests a possible short GRB with extended emission DATE: 25/09/13 18:17:13 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, Jean-Luc Atteia (IRAP), Stéphane Schanne (CEA) Report on behalf of the SVOM team: SVOM/GRM detected the burst GRB 250612A at 2025-09-12T21:06:23.700 UTC (T0), which is also detected by SVOM/ECLAIRs (Jean-Grégoire Ducoin et al., GCN #41820) and Fermi/GBM (Fermi GBM team, GCN #41819) With the event-by-event data downloaded through the X-band ground station, we conducted the standard analysis pipeline of GRB 250612A. The GRM light curve shows that this burst consists of a hard pulse followed by extended emission with a T90 of 13.0 +6.5/-2.0 s in the 15-5000 keV band, and there is a weak precursor-like signal at about T0-10 s, which is also clearly detected by ECLAIRs. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb250912A.png With the localization of ECLAIRs (RA= 14.953, DEC= 11.137), the time-averaged spectrum from T0-1 to T0+16 s can be fitted by a power law function with an exponential high-energy cutoff adequately. The power law index is -1.15 +0.19/- 0.15 and the cutoff energy, parameterized as Epeak, is 520 +692/-203 keV. The event fluence (10-1000 keV) in this time interval is (3.01 +0.40/- 0.44)E-06 erg/cm^2. Thus GRB 250912A is consistent with Type I GRBs in the 'Amati' relation diagram, as shown at: https://www.bursthub.cn//admin/static/svgrb250912A_amati.png Based on the location of this GRB in 'Amati' relation diagram, as well as the shape of the light curve, a possible merger origin is suggested. Follow-up observations are encouraged. We note that the calibration of SVOM/GRM is undergoing thus these results are preliminary. Refined analysis will be reported later. 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/GRM 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/41826. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39891] GRB 250912A:SVOM/VT optical upper limit
by GCN Circulars 13 Sep '25

13 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41825 SUBJECT: GRB 250912A:SVOM/VT optical upper limit DATE: 25/09/13 06:18:59 GMT FROM: Huali Li at at NAOC, SVOM <lhl(a)nao.cas.cn> H. L. Li, L. P. Xin, Y. N. Ma, Z. H. Yao, Y. L. Qiu, C. Wu, 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, D. H. Zhao (NAOC), J. Palmerio (CEA) report on behalf of the SVOM/VT team. SVOM performed an automatic slew on the burst triggered by SVOM/ECLAIRs (Ducoin et al., GCN 41820). SVOM/VT began observing the field at 2025-09-12T21:10:17 UTC, 233 sec after T0, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. No uncatalogued sources were detected in our single or stacked images at the SVOM/MXT position (Ducoin et al., GCN 41820), compared to the Legacy survey. The 3 sigma limits are: mid-time | exposure time (s) | band | upper limit (AB) -----------|-------------------|------|----------------- 12.8 min | 18*50 | VT_B | 23.0 12.8 min | 18*50 | VT_R | 23.1 Our results are consistent with the reports (Lipunov et al., GCN 41822; Wu et al., GCN 41824). 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/41825. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39890] GRB 250912A: LCO optical upper limit
by GCN Circulars 13 Sep '25

13 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41824 SUBJECT: GRB 250912A: LCO optical upper limit DATE: 25/09/13 03:14:55 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> C. Wu (NAOC), A. Saccardi (CEA/Irfu), L. P. Xin (NAOC), B. Cordier (CEA/Irfu), J.G. Ducoin (CPPM), D. Dornic (CPPM) report on behalf of the SVOM mission team: We observed the field of the GRB 250912A detected by Fermi/GBM(Fermi Team, GCN 41819) and SVOM/ECLAIRs (Ducoin et al., GCN 41820) with the LCO 1m telescope at South African Astronomical Observatory equipped with the Sinistro instrument. Our observation started on 2025-09-12 at 23:43:52 UT (~2.62 hr after the trigger) and we obtained 3x200 s exposures using the SDSS r filter. In the stacked image, we did not detect any new optical source at the SVOM/MXT position (Ducoin et al., GCN 41820). We derived the following upper limit r > 21.4 mag (3-sigma) calibrated using nearby stars from the UCAC4 catalog and not corrected for Galactic extinction. This project is funded by the SVOM collaboration. View this GCN Circular online at https://gcn.nasa.gov/circulars/41824. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39889] The EP-WXT trigger 01709240768 is likely a flaring star
by GCN Circulars 13 Sep '25

13 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41823 SUBJECT: The EP-WXT trigger 01709240768 is likely a flaring star DATE: 25/09/13 02:07:50 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> W.Chen, X. Mao, Z.X. Ling(NAO, CAS) on behalf of the Einstein Probe (EP) team: The EP-WXT trigger 01709240768 at the time of 2025-09-12T23:11:57 is likely a stellar flare associated with LSPM J0011+0227. The estimated flux of the flare is around 6x10^-11 erg/s/cm^2 in 0.5-4.0 keV, corresponding to an X-ray luminosity of around 1.2x10^31 erg/s. 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/41823. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39888] Fermi GRB 250912A: Global MASTER-Net observations report
by GCN Circulars 13 Sep '25

13 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41822 SUBJECT: Fermi GRB 250912A: Global MASTER-Net observations report DATE: 25/09/13 01:30:58 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 250912A ( Fermi GBM team, GCN 41819) errorbox 12109 sec after notice time and 12119 sec after trigger time at 2025-09-13 00:28:22 UT, with upper limit up to 17.0 mag. The observations began at zenith distance = 30 deg. The sun altitude is -24.7 deg. The galactic latitude b = -38 deg., longitude l = 125 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2990662 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 12149 | 2025-09-13 00:28:22 | MASTER-Kislovodsk | (00h 49m 11.26s , +24d 09m 10.4s) | C | 60 | 16.9 | 12323 | 2025-09-13 00:31:16 | MASTER-Kislovodsk | (00h 49m 55.02s , +26d 01m 05.3s) | C | 60 | 16.5 | 12820 | 2025-09-13 00:39:33 | MASTER-Kislovodsk | (00h 49m 13.73s , +24d 08m 45.3s) | C | 60 | 17.0 | 12996 | 2025-09-13 00:42:30 | MASTER-Kislovodsk | (00h 49m 58.92s , +26d 02m 34.8s) | C | 60 | 17.0 | 13174 | 2025-09-13 00:45:28 | MASTER-Kislovodsk | (00h 48m 26.82s , +22d 14m 39.0s) | C | 60 | 16.5 | 13353 | 2025-09-13 00:48:26 | MASTER-Kislovodsk | (01h 04m 52.12s , +22d 13m 05.7s) | C | 60 | 13.7 | 13436 | 2025-09-13 00:49:49 | MASTER-Kislovodsk | (00h 49m 14.02s , +24d 06m 49.9s) | C | 60 | 13.8 | 13521 | 2025-09-13 00:51:14 | MASTER-Kislovodsk | (01h 05m 50.94s , +24d 08m 56.8s) | C | 60 | 17.0 | 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/41822. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39887] EP250911a: Global MASTER-Net observations report
by GCN Circulars 13 Sep '25

13 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41821 SUBJECT: EP250911a: Global MASTER-Net observations report DATE: 25/09/13 00:18:39 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-Tavrida robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Russia (Lomonosov MSU, SAI Crimea astronomical station) was pointed to the EP250911a ( EP Team et al., GCN 41788) errorbox 27051 sec after notice time and 30571 sec after trigger time at 2025-09-11 17:27:59 UT, with upper limit up to 13.6 mag. Observations started at twilight. The observations began at zenith distance = 57 deg. The sun altitude is -15.9 deg. MASTER-Kislovodsk robotic telescope located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) was pointed to the EP250911a errorbox 1 days 51178 sec after notice time and 1 days 54698 sec after trigger time at 2025-09-13 00:10:06 UT, with upper limit up to 17.5 mag. The observations began at zenith distance = 34 deg. The sun altitude is -27.5 deg. The galactic latitude b = -32 deg., longitude l = 108 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2989778 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 13450 | 2025-09-11 12:42:07 | MASTER- | (23h 49m 56.46s , +28d 43m 10.6s) | C | 60 | 16.4 | Coadd 30602 | 2025-09-11 17:27:59 | MASTER-Tavrida | (23h 49m 27.05s , +29d 17m 08.7s) | C | 60 | 13.6 | 141129 | 2025-09-13 00:10:06 | MASTER-Kislovodsk | (23h 49m 03.03s , +29d 23m 20.1s) | C | 60 | 17.1 | 141292 | 2025-09-13 00:12:50 | MASTER-Kislovodsk | (23h 49m 01.01s , +29d 23m 04.4s) | C | 60 | 17.5 | 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/41821. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39886] GRB 250912A: SVOM detection of a burst
by GCN Circulars 12 Sep '25

12 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41820 SUBJECT: GRB 250912A: SVOM detection of a burst DATE: 25/09/12 21:58:10 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Jean-Grégoire Ducoin (CPPM), Damien Dornic (CPPM), Hui Yang (IRAP), Chenwei Wang (IHEP) , Hatsune Goto (Kanazawa Univ./CEA), report on behalf of the SVOM mission team: At 2025-09-12T21:06:24 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 250912A (SVOM burst-id sb25091206). This transient was also detected by Fermi/GBM (GCN Circular 41819). 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 14 alerts. IMT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 11.88 in the [8-120] keV energy band over a time window of 20.48 seconds starting at 2025-09-12T21:06:19. The localization of the best alert is R.A., Dec. 14.9546, 11.1084 degrees (J2000) with a 90% confidence level (C.L.) radius of 6.78 arcmin (including systematic error of 2 arcmin added in quadrature). This burst also triggered SVOM/GRM at 2025-09-12T21:06:23 on a timescale of 0.10 seconds with an SNR of 6.20. SVOM slewed to the burst. SVOM/MXT began observing the field at 2025-09-12T21:09:18 UTC, 174 seconds after T0. Using onboard processed data we found an uncatalogued X-ray source located at R.A., Dec. 14.953, 11.137 degrees: R.A. (J2000) = 0h59m48.72s Dec. (J2000) = 11d08m12.88s with a 90% C.L. radius of 143 arcseconds. This location is 1.7 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 Jean-Gregoire Ducoin: ducoin(a)cppm.in2p3.fr. Please contact the BA by email if you require additional information. View this GCN Circular online at https://gcn.nasa.gov/circulars/41820. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39885] GRB 250912A: Fermi GBM Final Real-time Localization
by GCN Circulars 12 Sep '25

12 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41819 SUBJECT: GRB 250912A: Fermi GBM Final Real-time Localization DATE: 25/09/12 21:17:50 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 21:06:23 UT on 12 Sep 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250912A (trigger 779403988.636734 / 250912879). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 13.9, Dec = 24.3 (J2000 degrees, equivalent to J2000 00h 55m, 24d 18'), with a statistical uncertainty of 7.9 degrees. The angle from the Fermi LAT boresight is 62.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250912879/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250912879/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250912879/… View this GCN Circular online at https://gcn.nasa.gov/circulars/41819. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39884] IceCube-Cascade 250911A: Upper limits from a search for additional neutrino events in IceCube
by GCN Circulars 12 Sep '25

12 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41818 SUBJECT: IceCube-Cascade 250911A: Upper limits from a search for additional neutrino events in IceCube DATE: 25/09/12 20:17:38 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-Cascade 250911A (https://gcn.gsfc.nasa.gov/notices_amon_icecube_cascade/141344_29341777.amon) in a time range of 1000 seconds centered on the alert event time (2025-09-11 04:20:17.140 UTC to 2025-09-11 04:36:57.140 UTC) during which IceCube was collecting good quality data. Excluding the event that prompted the alert, two track-like events are found within the 90% containment region of IceCube-Cascade 250911A. We find that these additional 2 events are well described by atmospheric background expectations, with a p-value of 0.01. IceCube’s sensitivity to neutrino point sources with an E^-2.5 spectrum, expressed as E^2 dN/dE evaluated at 1 TeV, ranges from 1.3e-01 to 6.1e+00 GeV cm^-2 within the 90% spatial containment region of IceCube-Cascade 250911A 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 3e+06 GeV. A subsequent search was performed including 2 days of data centered on the alert event time (2025-09-10 04:28:37.140 UTC to 2025-09-12 04:28:37.140 UTC). In this case, we report a p-value of 0.23, consistent with no significant excess of track events. IceCube’s sensitivity to neutrino point sources with an E^-2.5 spectrum, expressed as E^2 dN/dE evaluated at 1 TeV, ranges from 1.5e-01 to 6.2e+00 GeV cm^-2 within the 90% spatial containment of IceCube-Cascade 250911A 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/41818. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39883] LIGO/Virgo/KAGRA S250912s: 2 counterpart neutrino candidate events from an IceCube neutrino search
by GCN Circulars 12 Sep '25

12 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41817 SUBJECT: LIGO/Virgo/KAGRA S250912s: 2 counterpart neutrino candidate events from an IceCube neutrino search DATE: 25/09/12 20:13:49 GMT FROM: Zsuzsa Marka at IceCube/Columbia University <zsuzsa(a)astro.columbia.edu> IceCube Collaboration (http://icecube.wisc.edu/) reports: We have performed a search for track-like muon neutrino candidate events detected by IceCube consistent with the sky localization of the low-significance gravitational-wave candidate event S250912s in a time range of 1000 seconds centered on the alert event time (2025-09-12 18:13:09 UTC to 2025-09-12 18:29:49 UTC) [1,2]. During this time period, IceCube was collecting good quality data. A single hypothesis test was conducted using a Bayesian approach to quantify the joint GW + neutrino event significance, which assumes a binary merger scenario and accounts for known astrophysical priors, such as GW source distance, in the statistical significance estimation [3]. Two track-like events were found in spatial and temporal coincidence with the gravitational-wave candidate S250912s calculated from the map circulated in the S250912s-2-Preliminary notice. This represents an overall p-value of 0.00927 for the Bayesian search. The p-value measures the consistency of the observed track-like events with the known atmospheric backgrounds for this single map (not accounting for statistical trials from multiple GW events). Further details are available at https://gcn.nasa.gov/missions/icecube and at https://roc.icecube.wisc.edu/public/LvkNuTrackSearch. Properties of the coincident event are shown below: dt(s) RA(deg) Dec(deg) Angular uncertainty(deg) p-value(Bayesian) ------------------------------------------------------------------------------------- -276.12 284.52 44.13 16.11 0.0115 19.10 275.72 24.65 1.44 0.0530 where: dt = Time of track event minus time of GW trigger (sec) Angular uncertainty = Angular uncertainty of track event: the radius of a circle representing 90% CL containment by area. p-value = the individual p-value for the specific track event from this search. 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] M. G. Aartsen et al 2020 ApJL 898 L10 [2] Abbasi et al. Astrophys.J. 944 (2023) 1, 80 [3] I. Bartos et al. 2019 Phys. Rev. D 100, 083017 View this GCN Circular online at https://gcn.nasa.gov/circulars/41817. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39882] EP250908c: tentative VLT/FORS2 redshift z = 2.87
by GCN Circulars 12 Sep '25

12 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41816 SUBJECT: EP250908c: tentative VLT/FORS2 redshift z = 2.87 DATE: 25/09/12 16:10:17 GMT FROM: Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani(a)nbi.ku.dk> D. B. Malesani (DAWN/NBI and Radboud), L. Izzo (INAF/OACn and DARK/NBI), A. Saccardi (CEA/Irfu), J. An (NAOC), G. Corcoran (UCD), V. D’Elia (ASI/SSDC), M. Garnichey (LUX-Paris Obs.), P. G. Jonker (Radboud), A. J. Levan (Radboud and Warwick), A. Martin-Carrillo (UCD), E. Palazzi (INAF/OAS), G. Pugliese (API), D. Xu (NAOC), report on behalf of a larger collaboration: We observed the optical counterpart (Malesani et al., GCN 41760; Ma et al., GCN 41761; Rau, GCN 41773) of the fast X-ray transient EP250908c (Zhang et al., GCNs 41754, 41763) using the ESO VLT UT1 equipped with the FORS2 spectrograph. In the acquisition image (mid time 2025 Sep 9.134 UT, or 3.37 hr after the EP trigger) we measure a magnitude V = 21.4 +- 0.2 (calibrated using archival zeropoints). A spectrum covering the wavelength range 3800-8600 AA was secured using grism 300V and no order-sorting filter, with a total exposure time of 3x600 s. A faint trace is detected down to ~4790 AA, where a spectral break is observed. If due to Lyman alpha, this would correspond to a redshift of ~2.9. Consistently, a few, weak absorption features are detected, which can be interpreted as C II 1334, Si IV 1393,1402, Si II 1526, C IV 1548,1550, all at a common redshift of z = 2.87. Given the low S/N of the continuum, we caution that this redshift solution should be considered tentative. Rectifying what was stated in our previous report (Malesani et al., GCN 41760), we note the presence of an extended object in the Legacy Survey underlying the afterglow position, which is a candidate host galaxy for EP250908c. With a Legacy Survey magnitude of r = 23.1, this corresponds to M(UV) = -22.4 (AB) at z = 2.87. No emission lines are visible in our spectrum to determine the redshift of this object. We acknowledge excellent support from the observing staff in Paranal, in particular Julien Drevon, Jonathan Smoker and Marcela Espinoza. View this GCN Circular online at https://gcn.nasa.gov/circulars/41816. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39881] EP250911a: Upper limit from Fermi-GBM Observations
by GCN Circulars 12 Sep '25

12 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41815 SUBJECT: EP250911a: Upper limit from Fermi-GBM Observations DATE: 25/09/12 14:23:51 GMT FROM: mariaedvige.ravasio(a)ru.nl M. E. Ravasio and P.G. Jonker (Radboud Univ.) on behalf of the Einstein Probe Team and E. Burns (LSU) on behalf of the Fermi-GBM Team, report: Fermi-GBM had full spatial coverage of the transients EP250911a (Liang et al., GCN 41788 and GCN 41809) detected by EP-WXT, and found to be at z=3.84 (Malesani et al., GCN 41811). There was no Fermi-GBM onboard trigger around the refined EP trigger time T0=2025-09-11T08:57:55 (UTC). The GBM targeted search [1], the most sensitive, coherent search for GRB-like signals, was run in the time interval [T0-50; T0+500] s, seeking signals between 64 ms and 32.768 s in duration. No signal consistent with the EP transients, both temporally and spatially, is identified, as confirmed also by visual inspection of the data. Assuming a “normal” spectral template (Band function with Epeak = 230 keV, alpha = -1.0, beta = -2.3), whose alpha value is consistent with the power law index reported by EP (Liang et al., GCN 41809), and a timescale of 8.192 s, we derive a flux upper limit of 5.3e-08 erg/cm2/s in the energy band 10-1000 keV. [1] Goldstein et al. 2019 arXiv:1903.12597 View this GCN Circular online at https://gcn.nasa.gov/circulars/41815. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39880] LIGO/Virgo/KAGRA S250912f: Updated Sky localization
by GCN Circulars 12 Sep '25

12 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41814 SUBJECT: LIGO/Virgo/KAGRA S250912f: Updated Sky localization DATE: 25/09/12 13:28:26 GMT FROM: natalie.williams(a)uni-potsdam.de The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report: We have conducted further analysis of the LIGO Livingston Observatory (L1) and Virgo Observatory (V1) data around the time of the compact binary merger (CBC) candidate S250912f (GCN Circular 41810). 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/S250912f For the Bilby.multiorder.fits,0 sky map, the 90% credible region is 298 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 2740 +/- 722 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/41814. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39879] GRB 250911A: GECAM-B detection
by GCN Circulars 12 Sep '25

12 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41813 SUBJECT: GRB 250911A: GECAM-B detection DATE: 25/09/12 13:00:39 GMT FROM: zhangjinpeng(a)ihep.ac.cn Jin-Peng Zhang, Yang-Zhao Ren, Chen-Wei Wang, Shao-Lin Xiong and Yue Huang (IHEP) report on behalf of GECAM team: GECAM-B was triggered on-ground by GRB 250911A at 2025-09-11T01:29:28.250 UTC (denoted as T0), which was also observed by Swift (Palmer et al., GCN 41781). According to the GECAM-B light curves in about 40-6000 keV, this burst mainly consists of a weak precursor and a bright pulse with multiple spikes, with a duration (T90) of 35.4 +1.1/-1.7 s. The GECAM-B light curve can be found here: https://www.bursthub.cn//admin/static/gecambgrb250911A.png GECAM-B localized this burst to the following position (J2000): Ra: 262.0 deg Dec: -20.2 deg Err: 4.1 deg (1-sigma, statistical only) This localization is consistent with Swift observation (Palmer et al., GCN 41781; Beardmore et al., GCN 41784). The time-averaged spectrum from T0 - 5 s to T0 + 40 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.52 +0.10/-0.12 and the cutoff energy, parameterized as Epeak, is 330 +180/-80 keV. The event fluence (10-1000 keV) in this time interval is (3.52 +0.25/-0.32)E-05 erg/cm^2. The 'Amati' relation diagram of GRB 250911A is shown at: https://www.bursthub.cn//admin/static/gecambgrb250911A_amati.png Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) mission originally consists of two micro-satellites (GECAM-A and GECAM-B) launched in Dec. 2020. As the third member of GECAM constellation, GECAM-C was launched onboard SATech-01 experimental satellite in July 2022. GECAM mission is funded by the Chinese Academy of Sciences (CAS). View this GCN Circular online at https://gcn.nasa.gov/circulars/41813. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39878] GRB 250911A: Swift-BAT refined analysis
by GCN Circulars 12 Sep '25

12 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41812 SUBJECT: GRB 250911A: Swift-BAT refined analysis DATE: 25/09/12 10:16:27 GMT FROM: Rahul Gupta at NASA GSFC <rahul.gupta(a)nasa.gov> D. M. Palmer (LANL), 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), 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+200 sec from the recent telemetry downlink, we report further analysis of BAT GRB 250911 A (trigger #1348587) (Klingler, et al., GCN Circ. 41781). The BAT ground-calculated position is RA, Dec = 263.752, -16.841 deg which is RA(J2000) = 17h 35m 00.6s Dec(J2000) = -16d 50' 28.0" with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment). The partial coding was 29%. The mask-weighted BAT light curve shows two emission episodes (a precursor followed by main emission) separated by quiescent gap of ~ 80 sec. T90 (15-350 keV) is 128.42 +- 87.23 sec (estimated error including systematics). The time-averaged spectrum from T-1.35 to T+147.24 sec is best fit by a power law with an exponential cutoff. This fit gives a photon index 1.00 +- 0.20, and Epeak of 170.5 +- 84.5 keV (chi squared 56.83 for 56 d.o.f.). For this model the total fluence in the 15-150 keV band is 1.5 +- 0.0 x 10^-05 erg/cm2 and the 1-sec peak flux measured from T+103.94 sec in the 15-150 keV band is 8.6 +- 0.6 ph/cm2/sec. A fit to a simple power law gives a photon index of 1.35 +- 0.05 (chi squared 66.73 for 57 d.o.f.). 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/1348587 View this GCN Circular online at https://gcn.nasa.gov/circulars/41812. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39877] EP250911a: GTC/OSIRIS+ spectroscopic redshift z = 3.84
by GCN Circulars 12 Sep '25

12 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41811 SUBJECT: EP250911a: GTC/OSIRIS+ spectroscopic redshift z = 3.84 DATE: 25/09/12 09:59:04 GMT FROM: Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani(a)nbi.ku.dk> D. B. Malesani (DAWN/NBI and Radboud), A. J. Levan (Radboud and Warwick), G. Corcoran (UCD), R. A. J. Eyles-Ferris (Leicester), P. G. Jonker (Radboud), A. Martin-Carrillo (UCD), A. L. Cabrera Lavers (GTC), D. Reverte-Payá (GTC), A. Pérez-Romero (GTC) report for a larger collaboration: We observed the afterglow (Quirola-Vasquez et al., GCN 41790; Angulo et al., GCN 41793; Lai et al., GCN 41801; Evans et al., GCN 41802; Moskvitin & Spiridonova, GCN 41805; Ma et al., GCN 41807) of EP250911a (Liang et al. GCN 41788; Liang et al., GCN 41809) using the Gran Telescopio Canairas (GTC) equipped with the OSIRIS+ instrument. In a sequence of images taken in the r and z filters (mean times 13.97 and 14.12 hr after the trigger time, respectively), we measure magnitudes r = 22.0 +/- 0.1, z = 21.4 +/- 0.1 (all AB, calibrated against nearby Pan-STARRS objects, and not corrected for Galactic extinction). A sequence of 4 spectra with 1200 s exposure time each was obtained using the R1000B grism, covering the wavelength range 3700-7700 AA (mean time 15.4 hr after trigger). Inspection of the combined spectrum shows a weak continuum. A broad trough is observed around 5890 AA, which is interpreted as a DLA feature at a redshift z ~ 3.84. This is confirmed by the detection of a few metal absorption lines at a consistent redshift, among which we identify S II / Si II 1260, O II / Si II 1303, C II 1334, Si IV 1394, C IV 1548,1550. We also detect a continuum break around 4400 AA, which corresponds to the Lyman limit at this redshift. Note that, despite some temporal and spatial proximity, this redshift is inconsistent with the distance (~1.1 Gpc) derived for the LVK GW source S250911ac (LVK collaboration, GCNs 41786, GCN 41795), excluding an association between the two events. View this GCN Circular online at https://gcn.nasa.gov/circulars/41811. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39876] LIGO/Virgo/KAGRA S250912f: Identification of a GW compact binary merger candidate
by GCN Circulars 12 Sep '25

12 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41810 SUBJECT: LIGO/Virgo/KAGRA S250912f: Identification of a GW compact binary merger candidate DATE: 25/09/12 07:24:18 GMT FROM: Trang Nguyen <trang.nguyen(a)ligo.org> The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report: We identified the compact binary merger candidate S250912f during real-time processing of data from LIGO Livingston Observatory (L1) and Virgo Observatory (V1) at 2025-09-12 06:40:08.840 UTC (GPS time: 1441694426.840). The candidate was found by the GstLAL [1] and SPIIR [2] analysis pipelines. S250912f is an event of interest because its false alarm rate, as estimated by the online analysis, is 2.9e-13 Hz, or about one in 1e5 years. The event's properties can be found at this URL: https://gracedb.ligo.org/superevents/S250912f The classification of the GW signal, in order of descending probability, is BBH (>99%), Terrestrial (<1%), NSBH (<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%. [3] Using the masses and spins inferred from the signal, the probability of matter outside the final compact object (HasRemnant) is <1%. [3] 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 (44.0, 88.0) 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,1, an initial localization generated by BAYESTAR [4], distributed via GCN and SCiMMA notices about 27 seconds after the candidate event time. * bayestar.multiorder.fits,2, an initial localization generated by BAYESTAR [4], 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,2. For the bayestar.multiorder.fits,2 sky map, the 90% credible region is 393 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 2870 +/- 784 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] Chu et al. PRD 105, 024023 (2022) doi:10.1103/PhysRevD.105.024023 [3] Chatterjee et al. ApJ 896, 54 (2020) doi:10.3847/1538-4357/ab8dbe [4] Singer & Price PRD 93, 024013 (2016) doi:10.1103/PhysRevD.93.024013 View this GCN Circular online at https://gcn.nasa.gov/circulars/41810. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39875] EP250911a: refined analysis of the EP-WXT and EP-FXT observations
by GCN Circulars 12 Sep '25

12 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41809 SUBJECT: EP250911a: refined analysis of the EP-WXT and EP-FXT observations DATE: 25/09/12 05:02:03 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Y. F. Liang (PMO), Q. Y. Wu, W. D. Zhang(NAO, CAS) on behalf of the Einstein Probe (EP) team: The fast X-ray transient EP250911a triggered the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Liang et al., GCN 41788), and followed by Swift/XRT (Evans et al., GCN 41802) and several optical telescopes (Quirola-Vasquez et al., GCN 41790 , Angulo et al., GCN 41793, Lai et al., GCN 41801, Moskvitin et al., GCN 41805, Ma et al., GCN 41807). The refined analysis of the WXT data shows that the event started at T0=2025-09-11T08:57:55 (UTC) and lasted for 34 s with the peak flux of 9.3 x 10^(-9) erg/s/cm^2, before the observation was interrupted by the autonomous follow-up observation. The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 4.79 x 10^20 cm^-2 and a photon index of 0.77 (-/+0.95). The derived average unabsorbed 0.5-4 keV flux is 3.4 (-1.5/+3.1) x 10^(-9) erg/s/cm^2. The autonomous observation by the Follow-up X-ray Telescope (FXT) was performed at 2025-09-11T09:03:21 (UTC), about six minutes after T0. The exposure time of this observation is 3856 s. The on-ground analysis shows that an uncatalogued source was detected at R.A., Dec. = 357.5194, 29.2999 deg (J2000) with an uncertainty of about 10 arcsec (radius, 90% C.L. statistical and systematic). The average FXT 0.5-10 keV spectrum can be fitted with an absorbed power law with a fixed Galactic equivalent hydrogen column density of 4.79 x 10^20 cm^-2 and a photon index of 2.02 (-/+0.22). The derived average unabsorbed 0.5-10 keV flux is 7.5 (-1.1/+1.4) x 10^(-13) 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/41809. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39874] GRB 250910B: SVOM/GRM observation
by GCN Circulars 12 Sep '25

12 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41808 SUBJECT: GRB 250910B: SVOM/GRM observation DATE: 25/09/12 04:13:28 GMT FROM: Chenwei Wang at IHEP <cwwang(a)ihep.ac.cn> SVOM/GRM team: Chen-Wei Wang, Yue Huang, Shi-Jie Zheng, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Jean-Luc Atteia (IRAP) Report on behalf of the SVOM team: SVOM/GRM was triggered in-flight by a burst GRB 250910B (SVOM trigger reference: sb25091008) at 2025-09-10T18:52:06.000 UTC (T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN #41778). 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 10.0 +4.5/-1.5 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb250910B.png In addition, the position of this burst, as determined by Fermi/GBM (RA = 80.2, Dec = -46.4, GCN #41778), is located at about 54 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 the localization from Fermi/GBM, the time-averaged spectrum from T0-3 to T0+8.5 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -0.75 +0.12/-0.11 and the cutoff energy, parameterized as Epeak, is 218 +29/-22 keV. The event fluence (10-1000 keV) in this time interval is (5.77 +0.38/-0.36)E-06 erg/cm^2. The 'Amati' relation diagram of GRB 250910B is shown at: https://www.bursthub.cn//admin/static/svgrb250910B_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/41808. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39873] EP250911a: SVOM/VT optical observation
by GCN Circulars 12 Sep '25

12 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41807 SUBJECT: EP250911a: SVOM/VT optical observation DATE: 25/09/12 03:27:06 GMT FROM: Yinuo Ma <mayn(a)bao.ac.cn> Y. N. Ma, L. P. Xin, Z. H. Yao, 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 performed a Target of Opportunity observation of EP250911a detected by EP/WXT (Liang et al., GCN 41788). SVOM/VT began observing the field at 2025-09-11T15:33:30 UTC, 6.584 hours after the trigger, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. With X-band data available, the optical counterpart (Quirola-Vasquez et al., GCN 41790, Angulo et al., GCN 41793; Lai et al., GCN 41801; Moskvitin & Spiridonova, GCN 41805) at a location consistent with Swift XRT position (Evans et al., GCN 41802) was clearly detected in both VT_B and VT_R bands. The magnitudes are: mid time (h) | exposure time (s) | band | mag (AB) | mag err -------------|-------------------|------|----------|-------- 6.945 | 27*100 | VT_B | 22.06 | 0.08 6.945 | 27*100 | VT_R | 20.87 | 0.05 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/41807. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39872] GRB 250911A: MASTER optical counterpart observations
by GCN Circulars 12 Sep '25

12 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41806 SUBJECT: GRB 250911A: MASTER optical counterpart observations DATE: 25/09/12 00:53:31 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.M.Lipunov (Lomonosov MSU, Moscow), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (OAFA), A.Kuznetsov, A.Sankovich, G.Antipov, P.Balanutsa, E.Gorbovskoy, N.Tiurina, M.Shilova, A.Chasovnikov, V.Topolev, K.Zhirkov, Ya.Kechin, V.Senik, D.Vlasenko (Lomonosov MSU), D.Buckley, (SAAO, South Africa) O.Gress, N.Budnev (ISU, Irkutsk), A.Sosnovskij (Crao RAS), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), V.M.Pillet, R.Rebolo Lopez (The Instituto de Astrofisica de Canarias, Spain), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez,J.Martinez,A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysic Observatory, Mexico) MASTER-OAFA robotic telescope (Global MASTER-Net: http://observ.pereplet.ru,Argentina started Swift GRB 250911A (Klingler et al. GCN 41781) observations automatically at 2025-09-11 02:25:44UT and in own planner mode befor it. There is GRB optical counterpart MASTER OT J173500.02-165114.40 with mOT~18.81 at Swift position (XRT Perri et al. GCN 41783, Beardmore et al. GCN 41784, Dichiara et al. GCN 41804; UVOT Siegel et al. GCN 41800), first reported by COLIBRI (Angula et al. GCN 41782). All images reduction will be continued. The message may be cited. References 1) Lipunov et al. 2010, MASTER Robotic Net, Advances in Astronomy, vol. 2010, p.30L 2) Lipunov,V.G. Kornilov, E.S. Gorbovskoy, N.V. Tyurina, A.S. Kuznetsov, "ASTRONOMICAL ROBOTIC NETWORKS and OPERATIVE MULTICHANNEL ASTROPHYSICS. Based on the example of the global MASTER network.", The Moscow State University Publishing House. In the series "Works of Outstanding Scientists of Moscow State University", http://www.pereplet.ru/lipunov/625.html#625) View this GCN Circular online at https://gcn.nasa.gov/circulars/41806. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39871] EP250911a: SAO RAS optical observations
by GCN Circulars 11 Sep '25

11 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41805 SUBJECT: EP250911a: SAO RAS optical observations DATE: 25/09/11 23:47:13 GMT FROM: Alexander Moskvitin at SAO RAS <mosk(a)sao.ru> A. Moskvitin, O. Spiridonova (SAO RAS) report on behalf of GRB follow-up collaboration. We observed the field of EP250911a (Liang et al., GCN 41788, Evans et al., GCN 41802) with the 1-m SAO RAS telescope Zeiss-1000 equipped with CCD-photometer. We obtained 9 x 300 sec. images in Rc band on September 11, 21:38:05--22:34:14 UT (t_mid - T0 = 13.12819 hours = 0.547008 days). The OT (Quirola-Vasquez et al., GCN 41790, Angulo et al., GCN 41793; Lai et al., GCN 41801) is clearly detected in the stacked image with the brightness of R = 21.90 +/- 0.11 (R_lim = 23.0 mag). This preliminary photometry is based on nearby SDSS stars (magnitudes were converted with the Lupton 2005 equations) and not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/41805. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39870] GRB 250911A: Swift-XRT refined Analysis
by GCN Circulars 11 Sep '25

11 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41804 SUBJECT: GRB 250911A: Swift-XRT refined Analysis DATE: 25/09/11 20:18:36 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> S. Dichiara (PSU), J.A. Kennea (PSU), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), V. D'Elia (SSDC & INAF-OAR), B. Sbarufatti (INAF-OAB), C. Salvaggio (INAF-OAB), D.N. Burrows (PSU) and P.A. Evans report on behalf of the Swift-XRT team: We have analysed 6.6 ks of XRT data for GRB 250911A, from 3.4 ks to 48.4 ks after the trigger. The data are entirely in Photon Counting (PC) mode. The light curve can be modelled with a power-law decay with a decay index of alpha=1.52 (+/-0.08). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.80 (+0.16, -0.15). The best-fitting absorption column is 3.9 (+1.0, -0.5) x 10^21 cm^-2, consistent with the Galactic value of 3.4 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 4.5 x 10^-11 (6.3 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 3.9 (+1.0, -0.5) x 10^21 cm^-2 Galactic foreground: 3.4 x 10^21 cm^-2 Excess significance: <1.6 sigma Photon index: 1.80 (+0.16, -0.15) If the light curve continues to decay with a power-law decay index of 1.52, the count rate at T+24 hours will be 0.015 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 6.8 x 10^-13 (9.5 x 10^-13) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01348587. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/41804. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39869] GRB 250910C: Fermi GBM Final Localization Correction
by GCN Circulars 11 Sep '25

11 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41803 SUBJECT: GRB 250910C: Fermi GBM Final Localization Correction DATE: 25/09/11 18:28:00 GMT FROM: eliza.neights(a)gmail.com The Fermi GBM team reports the detection of a likely LONG GRB "At 23:50:11.34 UT on 10 September 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250910C (trigger 779241016/250910993). This trigger was initially classified as Unreliable location by the flight software, but is in fact a GRB. The on-ground calculated location, using the Fermi GBM trigger data, is RA = 47.58, Dec = -35.77 (J2000 degrees, equivalent to J2000 3h 10m, -35d 46'), with a statistical uncertainty of 10.95 degrees. The angle from the Fermi LAT boresight is 46 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250910993/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250910993/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250910993/…" View this GCN Circular online at https://gcn.nasa.gov/circulars/41803. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39868] EP250911a: Swift-XRT observations
by GCN Circulars 11 Sep '25

11 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41802 SUBJECT: EP250911a: Swift-XRT observations DATE: 25/09/11 17:36:52 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 EP250911a (Liang et al., GCN Circ 41788), collecting 1.7 ks of Photon Counting (PC) mode data between T0+5.5 ks and T0+11 ks after the trigger. We have detected 1 source consistent with the EP/FXT position (Liang et al., GCN Circ 41788). This has been automatically classified as an uncatalogued X-ray source. Uncatalogued X-ray sources -------------------------- Source 1 (SWIFT J235004.5+291757): ================================== RA (J2000.0): 357.5191 = 23 50 04.58 Dec (J2000.0): +29.2992 = +29 17 57.1 Error: 4.6 (arcsec, radius, 90% confidence). Detect flag: GOOD Distance: 62 arcsec from the Einstein Probe/WXT position. Mean rate: 0.0239 +/- 0.0047 ct s^-1 Mean flux: (8.3 +/- 1.6)e-13 erg cm^-2 s^-1 Peak rate: 0.0239 +/- 0.0047 ct s^-1 Peak flux: (8.3 +/- 1.6)e-13 erg cm^-2 s^-1 ECF: 3.47e-11 erg cm^-2 ct^-1 assuming NH=5.84e+20 cm^-2, gamma=1.92 determined from a spectral fit. XMM UL: 7.6e-12 erg cm^-2 s^-1, (0.3-10 keV) so the source is not above this 3-sigma upper limit. 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. We note that source 1 also matches the position of the optical counterpart to EP250911a reported by Quirola-Vasquez et al. (GCN Circ. 41790) and Angulo et al. (GCN Circ. 41793). 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_FIELD00073. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/41802. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39867] EP250911a: Optical detection with Kinder observations
by GCN Circulars 11 Sep '25

11 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41801 SUBJECT: EP250911a: Optical detection with Kinder observations DATE: 25/09/11 17:32:52 GMT FROM: Janet Chen at National Central University <janetstars(a)gmail.com> C.-H. Lai, A. Aryan, T.-W. Chen, C.-S. Lin (all NCU), Y.-C. Shiau (FEMH), J. Gillanders, S. J. Smartt (both Oxford), Y. J. Yang (NYUAD), A. K. H. Kong (NTHU), Y.-H. Lee, A. Sankar. K, Y.-C. Pan, C.-C. Ngeow, M.-H. Lee, W.-J. Hou, H.-C. Lin, H.-Y. Hsiao, J.-K. Guo (all NCU), S. Yang, Z. N. Wang, L. L. Fan, G. H. Sun (all HNAS), H.-W. Lin (UMich), H. F. Stevance, S. Srivastav, L. Rhodes (all Oxford), M. Nicholl, M. Fulton, T. Moore, K. W. Smith, C. Angus, A. Aamer (all QUB), A. Schultz and M. Huber (both IfA, Hawaii) report: We observed the field of the fast X-ray transient EP250911a (Liang et al., GCN 41788) using the 1m LOT and 40cm SLT at Lulin Observatory in Taiwan as part of the Kinder collaboration (Chen & Yang et al., 2025, ApJ, 983, 86). The first LOT epoch of observations in r-band started at 13:17 UTC on the 11th of September 2025 (MJD 60929.554), 4.31 hr after the EP WXT trigger. Moreover, the first SLT epoch of observations in i-band started at 13:18 UTC on the 11th of September 2025 (MJD 60929.554), 4.33 hr after the EP WXT trigger. We utilized the astroalign (Beroiz et al. 2020, A&C, 32, 100384) and astropy (Astropy Collaboration et al. 2022, ApJ, 935, 167) packages to align and stack the individual frames. In the stacked frames of r, i and z bands from LOT and i-band from SLT, we clearly detected the optical counterpart candidate proposed by Quirola-Vasquez et al. (GCN 41790) and confirmed by Angulo et al. (GCN 41793). Moreover, we further utilized AutoPhOT to perform the PSF photometry. The details of the observations and the measured magnitude (in the AB system) are as follows: Telescope | Filter | MJD (start) | t-t0 (hr | Exposure (s) | Magnitude | avg. Seeing | med. Airmass LOT | r | 60929.554 | 4.31 | 300 * 6 | 21.30 +/- 0.05 | 0".74 | 1.29 SLT | i | 60929.554 | 4.33 | 300 * 24 | 20.44 +/- 0.11| 1".3 | 1.14 LOT | i | 60929.601 | 5.46 | 300 * 6 | 20.71 +/- 0.07 | 0".73 | 1.10 LOT | z | 60929.642 | 6.43 | 300 * 6 | 20.50 +/- 0.09 | 0".97| 1.02 The presented magnitudes are calibrated using the field stars from the SDSS catalog and are not corrected for the expected Galactic foreground reddening of E(B-V) = 0.05 mag in the direction of the transient (Schlafly & Finkbeiner 2011). View this GCN Circular online at https://gcn.nasa.gov/circulars/41801. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39866] GRB 250911A: Swift/UVOT Detection
by GCN Circulars 11 Sep '25

11 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41800 SUBJECT: GRB 250911A: Swift/UVOT Detection DATE: 25/09/11 16:49:55 GMT FROM: Mike Siegel at PSU/Swift MOC <mhs18(a)psu.edu> M. H. Siegel (PSU) and N. J. Klingler (GSFC/UMBC/CRESSTII) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 250911A 3.5 ks after the BAT trigger (Klingler et al., GCN Circ. 41781). A fading afterglow consistent the XRT position (Beardmore et al., GCN Circ. 41784) and COLIBRI afterglow (Angulo et al., GCN Circ. 41782) is detected in the initial UVOT exposures. The preliminary UVOT position is: RA (J2000) = 17:35:00.03 = 263.75011 (deg.) Dec (J2000) = -16:51:14.9 = -16.85413 (deg.) with an estimated uncertainty of 0.42 arc sec. (radius, 90% confidence). Preliminary 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first finding chart (FC) exposure and subsequent exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag/3sigUL white 3483 4252 344 19.95+/-0.16 v 4462 4662 196 >19.20 v 26629 26655 25 >17.87 b 3847 4047 196 19.40+/-0.22 b 10440 10955 503 20.58+/-0.33 u 3642 5214 330 19.18+/-0.19 u 21026 21075 48 >18.94 uvw1 4872 5072 196 >19.53 uvw1 20120 21019 885 >20.01 uvm2 4667 4867 196 >19.38 uvm2 16021 16815 782 >20.49 uvw2 4258 4458 196 >19.50 uvw2 25723 26622 885 >20.09 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.4185 in the direction of the burst (Schlegel et al. 1998). View this GCN Circular online at https://gcn.nasa.gov/circulars/41800. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39865] GRB 250910A / EP250910a: Swift-XRT afterglow detection
by GCN Circulars 11 Sep '25

11 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41799 SUBJECT: GRB 250910A / EP250910a: Swift-XRT afterglow detection DATE: 25/09/11 16:29:52 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> S. Lanava (PSU), S. Dichiara (PSU), J.A. Kennea (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), M. Perri (SSDC & INAF-OAR), V. D'Elia (SSDC & INAF-OAR), B. Sbarufatti (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 250910A. We searched for X-ray sources in 1.2 ks of Photon Counting (PC) mode data. The total exposure at the position of the afterglow (see below) is 1.2 ks, obtained between T0+29.5 ks and T0+30.7 ks. An uncatalogued X-ray source is detected and is believed to be the afterglow. Using 1195 s of PC mode data and 1 UVOT image, we find an enhanced XRT position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 39.80164, -39.69498 which is equivalent to: RA (J2000): 02h 39m 12.39s Dec(J2000): -39d 41' 41.9" with an uncertainty of 8.4 arcsec (radius, 90% confidence). This source is consistent with the position reported by EP/FXT (Liu et al., GCN 41776) and with the optical/NIR source detected with VLT (Schneider et al., GCN 41794) and SVOM/VT (Li et al., GCN 41798). We cannot determine at the present time whether the source is fading. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/03000083. The results of the full analysis of the XRT observations are available at https://www.swift.ac.uk/SVOM/SVOM_FIELD00036. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/41799. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39864] GRB 250910A / EP250910a: SVOM/VT afterglow confirmation
by GCN Circulars 11 Sep '25

11 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41798 SUBJECT: GRB 250910A / EP250910a: SVOM/VT afterglow confirmation DATE: 25/09/11 15:27:28 GMT FROM: Huali Li at at NAOC, SVOM <lhl(a)nao.cas.cn> H.L. Li (NAOC), Y.N. Ma, L.P. Xin, Y. L. Qiu, C. Wu, 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), D. H. Zhao, J. Palmerio (CEA) report on behalf of the SVOM/VT team. SVOM/VT performed an automatic slew on the burst triggered by SVOM/ECLAIRs (Ma et al., GCN 41769) and EP-WXT (Liu et al., GCN 41776). The observation with good image quality began at 2025-09-10T04:00:48 UTC, ie. 44 min post trigger in VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. A second ToO observation was performed to the field (Wu et al., GCN 41772; Li et al., GCN 41774; Garnichey et al., GCN 41777; Lipunov et al., GCN 41789), which stared at 2025-09-11T09:10:42 UTC, i.e., 1.24 day post trigger. The NIR counterpart reported by VLT (Schneider et al., GCN 41794) in the errorbox of SVOM/MXT (Götz et al., GCN 41770), EP-FXT (Liu et al., GCN 41776) and Swift/XRT (https://www.swift.ac.uk/SVOM/SVOM_FIELD00036/) was detected in our stacked images in both channels. It was fading from our earliest observation at about 22.7+/-0.3 mag to 23.6+/-0.4 mag (1.27 days) in VT_R band. 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/41798. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39863] GRB 250909B: Insight-HXMT detection
by GCN Circulars 11 Sep '25

11 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41797 SUBJECT: GRB 250909B: Insight-HXMT detection DATE: 25/09/11 15:16:08 GMT FROM: Chenwei Wang at IHEP <cwwang(a)ihep.ac.cn> Chen-Wei Wang, Shao-Lin Xiong, and Chao Zheng report on behalf of the Insight-HXMT team: At 2025-09-09T17:49:10.200 (T0), Insight-HXMT/HE detected the burst GRB 250909B, which is also detected by AstroSat (M. Tembhurnikar et al., GCN#41775), SVOM/GRM (Wang et al., GCN#41796) and Konus-Wind. The Insight-HXMT/HE light curve mainly consists of multi-pulses with a T90 of 12.9 +1.2/-1.7 s. The 1s peak rate, measured from T0+0.250 s, is 5422 cnts/sec. The total counts from this burst is 23044 counts. The HXMT/HE light curve can be found here: https://www.bursthub.cn//admin/static/hxmtgrb250909B.png All measurements above are made with the CsI detectors operating in the regular mode with the energy range of about 60-900 keV (deposited energy). Only gamma-rays with energy greater than about 200 keV can penetrate the spacecraft and leave signals in the CsI detectors installed inside of the telescope. Insight-HXMT is the first Chinese space X-ray telescope, which was funded jointly by the China National Space Administration (CNSA) and the Chinese Academy of Sciences (CAS). More information about it could be found at: http://www.hxmt.org. View this GCN Circular online at https://gcn.nasa.gov/circulars/41797. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39862] GRB 250909B: SVOM/GRM observation
by GCN Circulars 11 Sep '25

11 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41796 SUBJECT: GRB 250909B: SVOM/GRM observation DATE: 25/09/11 15:07:29 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: Jean-Luc Atteia (IRAP) Report on behalf of the SVOM team: SVOM/GRM was triggered on-ground by GRB 250909B at 2025-09-09T17:49:10.200 UTC (T0), which is also detected by AstroSat (M. Tembhurnikar et al., GCN#41775) and Konus-Wind. With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of a multi-pulses with a T90 of 10.5 +3.5/-1.5 s in the 15-5000 keV band. ECLAIRs was not collecting data at the time of this burst. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb250909B.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/41796. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39861] LIGO/Virgo/KAGRA S250911ac: Updated Sky localization and Source Classification
by GCN Circulars 11 Sep '25

11 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41795 SUBJECT: LIGO/Virgo/KAGRA S250911ac: Updated Sky localization and Source Classification DATE: 25/09/11 13:17:25 GMT FROM: natalie.williams(a)uni-potsdam.de The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report: We have conducted further analysis of the LIGO Hanford Observatory (H1) and LIGO Livingston Observatory (L1) data around the time of the compact binary merger (CBC) candidate S250911ac (GCN Circular 41786). Parameter estimation has been performed using Bilby [1] and a new sky map, Bilby.offline0.multiorder.fits,0, distributed via GCN and SCiMMA notices, is available for retrieval from the GraceDB event page: https://gracedb.ligo.org/superevents/S250911ac %}Assuming the candidate is astrophysical, the updated classification of the GW signal, in order of descending probability, is BBH (96%), Terrestrial (4%), BNS (<1%), or NSBH (<1%). For the Bilby.offline0.multiorder.fits,0 sky map, the 90% credible region is 952 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 1124 +/- 285 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/41795. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39860] GRB 250910A / EP250910a : VLT/HAWK-I NIR counterpart discovery
by GCN Circulars 11 Sep '25

11 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41794 SUBJECT: GRB 250910A / EP250910a : VLT/HAWK-I NIR counterpart discovery DATE: 25/09/11 12:51:17 GMT FROM: Benjamin Schneider at MIT <bschn(a)mit.edu> B. Schneider (LAM), A. Martin-Carrillo (UCD), M. Garnichey (LUX-Paris Obs.), V. D'Elia (ASI-SSDC), A. J. Levan (Radboud U.), G. Corcoran (UCD), D. B. Malesani (DAWN/NBI and Radboud), A. Saccardi (CEA/Irfu), A. L. Thakur (INAF-IAPS), S. D. Vergani (LUX-Paris Obs.) report on behalf of the Stargate collaboration: We observed again the field of GRB 250910A / EP250910a (Ma et al., GCN 41769; Götz et al. GCN 41770; Wu et al., GCN 41772; Li et al., GCN 41774; Liu et al., GCN 41776) using the ESO VLT UT4 (Yepun) equipped with the HAWK-I NIR camera. We obtained 15 min imaging in the J band, beginning on 2025-09-11 at 09:36:48 UT (1.26 days post-trigger). Carrying out image subtraction with HOTPANTS between our new and previous (Garnichey et al., GCN 41777) images, a clear transient source is detected at coordinates (0.5" error): RA(J2000) = 02:39:12.56 Dec(J2000) = -39:41:40.9 These coordinates are consistent with the EP/FXT X-ray location (Liu et al., GCN 41776) and Swift/XRT X-ray detection (https://www.swift.ac.uk/SVOM/SVOM_FIELD00036/) We measure for the transient a magnitude J = 22.73 +/- 0.08 (AB, at 5.2 hr post trigger), calibrated against nearby 2MASS stars and not corrected for Galactic extinction. We caution that strictly this is a lower limit to the source brightness, as it is possible that residual transient light was present in our second observation. The spatial association with the X-ray afterglow and its fading behavior indicate that this object is the NIR afterglow of GRB 250910A / EP250910a. We note that at this location, an extended optical source can be seen in the Legacy Survey (magnitudes g = 24.56, r = 23.80, i = 23.38, z = 23.66), likely being the host galaxy of this source. We acknowledge excellent support from the ESO observing staff in Paranal, in particular Juan Carlos Olivares and Robert De Rosa. View this GCN Circular online at https://gcn.nasa.gov/circulars/41794. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39859] EP250911a: COLIBRÍ optical observations
by GCN Circulars 11 Sep '25

11 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41793 SUBJECT: EP250911a: COLIBRÍ optical observations DATE: 25/09/11 12:10:52 GMT FROM: Rosa L. Becerra at Tor Vergata, Roma <rosa.becerra(a)roma2.infn.it> Camila Angulo (UNAM), Sarah Antier (OCA), Rosa L. Becerra (U Roma), Jean-Grégoire Ducoin (CPPM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Jean-Luc Atteia (IRAP), Fredd Alvarez (UNAM), Dalya Akl (NYUAD), 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 EP250711a (Liang et al., GCN Circ. 41788) using the DDRAGO wide-field imager on the COLIBRÍ telescope. We observed from 2025-11-09 09:29 to 10:33 UTC (from 0.52 to 1.58 hours after the trigger, and 13 minutes after the notice) and obtained 45 minutes of exposure in the r and z filters. 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 our both filters, we detected the optical counterpart reported by LCO (Quirola-Vasquez et al., GCN Circ. 41790), at preliminary magnitudes of: r = 20.57 +/- 0.02 z = 19.87 +/- 0.03 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/41793. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39858] LIGO/Virgo/KAGRA S250908y: Updated Sky localization
by GCN Circulars 11 Sep '25

11 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41792 SUBJECT: LIGO/Virgo/KAGRA S250908y: Updated Sky localization DATE: 25/09/11 11:27:49 GMT FROM: natalie.williams(a)uni-potsdam.de 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 S250908y (GCN Circular 41750). 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/S250908y For the Bilby.multiorder.fits,0 sky map, the 90% credible region is 9926 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 1146 +/- 334 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/41792. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39857] Fermi GRB 250910B: Global MASTER-Net observations report
by GCN Circulars 11 Sep '25

11 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41791 SUBJECT: Fermi GRB 250910B: Global MASTER-Net observations report DATE: 25/09/11 10:31:00 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 Fermi GRB 250910B ( Fermi GBM team, GCN 41778) errorbox 45057 sec after notice time and 45097 sec after trigger time at 2025-09-11 07:23:42 UT, with upper limit up to 19.9 mag. The observations began at zenith distance = 40 deg. The sun altitude is -41.7 deg. The galactic latitude b = -34 deg., longitude l = 252 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2989479 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 45128 | 2025-09-11 07:23:42 | MASTER-OAFA | (05h 21m 01.46s , -46d 16m 04.7s) | C | 60 | 19.9 | 45203 | 2025-09-11 07:24:58 | MASTER-OAFA | (05h 21m 06.25s , -46d 17m 02.2s) | C | 60 | 19.8 | 45277 | 2025-09-11 07:26:12 | MASTER-OAFA | (05h 21m 01.18s , -46d 17m 59.3s) | C | 60 | 19.9 | 45353 | 2025-09-11 07:27:28 | MASTER-OAFA | (05h 21m 05.78s , -46d 17m 54.0s) | C | 60 | 19.9 | 45428 | 2025-09-11 07:28:43 | MASTER-OAFA | (05h 21m 03.82s , -46d 16m 02.0s) | C | 60 | 19.8 | 45503 | 2025-09-11 07:29:58 | MASTER-OAFA | (05h 21m 03.84s , -46d 17m 30.1s) | C | 60 | 19.8 | 45579 | 2025-09-11 07:31:13 | MASTER-OAFA | (05h 21m 06.46s , -46d 16m 12.8s) | C | 60 | 19.8 | 45656 | 2025-09-11 07:32:31 | MASTER-OAFA | (05h 21m 00.95s , -46d 16m 45.4s) | C | 60 | 19.8 | 45734 | 2025-09-11 07:33:49 | MASTER-OAFA | (05h 21m 01.87s , -46d 15m 42.5s) | C | 60 | 19.8 | 45811 | 2025-09-11 07:35:06 | MASTER-OAFA | (05h 21m 07.33s , -46d 16m 40.1s) | C | 60 | 19.9 | 45888 | 2025-09-11 07:36:22 | MASTER-OAFA | (05h 21m 00.65s , -46d 17m 37.5s) | C | 60 | 19.8 | 45962 | 2025-09-11 07:37:36 | MASTER-OAFA | (05h 21m 07.79s , -46d 17m 14.3s) | C | 60 | 19.9 | 46036 | 2025-09-11 07:38:51 | MASTER-OAFA | (05h 21m 04.04s , -46d 15m 34.4s) | C | 60 | 19.9 | 46112 | 2025-09-11 07:40:06 | MASTER-OAFA | (05h 21m 04.05s , -46d 17m 27.2s) | C | 60 | 19.9 | 46187 | 2025-09-11 07:41:21 | MASTER-OAFA | (05h 21m 07.22s , -46d 15m 29.4s) | C | 60 | 19.9 | 46263 | 2025-09-11 07:42:38 | MASTER-OAFA | (05h 21m 00.93s , -46d 16m 25.0s) | C | 60 | 19.9 | 46340 | 2025-09-11 07:43:55 | MASTER-OAFA | (05h 21m 00.54s , -46d 15m 22.3s) | C | 60 | 19.9 | 46417 | 2025-09-11 07:45:11 | MASTER-OAFA | (05h 21m 06.25s , -46d 16m 20.5s) | C | 60 | 19.8 | 46495 | 2025-09-11 07:46:29 | MASTER-OAFA | (05h 21m 01.68s , -46d 17m 18.0s) | C | 60 | 19.9 | 46569 | 2025-09-11 07:47:43 | MASTER-OAFA | (05h 21m 06.17s , -46d 16m 51.8s) | C | 60 | 19.9 | 46645 | 2025-09-11 07:49:00 | MASTER-OAFA | (05h 21m 04.24s , -46d 15m 24.7s) | C | 60 | 19.9 | 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/41791. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39856] EP250911a: LCO optical counterpart discovery
by GCN Circulars 11 Sep '25

11 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41790 SUBJECT: EP250911a: LCO optical counterpart discovery DATE: 25/09/11 10:23:38 GMT FROM: Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani(a)nbi.ku.dk> J. A. Quirola-Vasquez (Radboud), R. A. J. Eyles-Ferris (Leicester), D. B. Malesani (DAWN/NBI and Radboud), G. Corcoran (UCD), A. Martin-Carrillo (UCD), L. Cotter (UCD), P. G. Jonker (Radboud), F. E. Bauer (SSI and UTA), and J. Chacón (PUC) report on behalf of a larger collaboration: We observed the location of EP250911a (Liang et al., GCN 41788) with the Sinistro instrument mounted on the 1-m telescopes at McDonald Observatory, available via the LCO network. 6 x 200 s exposures were obtained in the SDSS r filter at a start time of 2025-09-11 UT 09:35:35 (~37.1 min post trigger). Within the WXT and FXT error circles (Liang et al., GCN 41788) we locate a new source in our stacked r-band image, not visible in the archival Legacy Survey images. Its coordinates (0.5" error) are: RA(J2000): 23:50:04.83 DEC(J2000): +29:17:59.6 Calibrated to nearby stars from the Pan-STARRS catalog, we measure a magnitude r = 20.04 +/- 0.07 (AB), not corrected for Galactic extinction. Given the non-detection in the deeper archival images and the consistency with the FXT error circle, we suggest that this source is the optical counterpart of EP250911a. View this GCN Circular online at https://gcn.nasa.gov/circulars/41790. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39855] EP250910a: Global MASTER-Net observations report
by GCN Circulars 11 Sep '25

11 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41789 SUBJECT: EP250910a: Global MASTER-Net observations report DATE: 25/09/11 10:09:24 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) was pointed to the EP250910a ( EP Team et al., GCN 41776) errorbox 829 sec after trigger time at 2025-09-10 03:29:53 UT, with upper limit up to 19.6 mag. The observations began at zenith distance = 54 deg. The sun altitude is -60.2 deg. The galactic latitude b = -64 deg., longitude l = 248 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2989175 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 849 | 2025-09-10 03:29:53 | MASTER-OAFA | (02h 39m 03.43s , -39d 42m 17.1s) | C | 40 | 18.9 | 895 | 2025-09-10 03:30:38 | MASTER-OAFA | (02h 39m 03.40s , -39d 42m 15.3s) | C | 40 | 18.9 | 940 | 2025-09-10 03:31:24 | MASTER-OAFA | (02h 39m 03.42s , -39d 42m 13.6s) | C | 40 | 18.9 | 987 | 2025-09-10 03:32:10 | MASTER-OAFA | (02h 39m 03.36s , -39d 42m 11.4s) | C | 40 | 18.9 | 1032 | 2025-09-10 03:32:55 | MASTER-OAFA | (02h 39m 03.34s , -39d 42m 09.8s) | C | 40 | 18.9 | 1077 | 2025-09-10 03:33:41 | MASTER-OAFA | (02h 39m 03.29s , -39d 42m 08.0s) | C | 40 | 18.9 | 1123 | 2025-09-10 03:34:27 | MASTER-OAFA | (02h 39m 03.28s , -39d 42m 06.1s) | C | 40 | 18.9 | 1169 | 2025-09-10 03:35:13 | MASTER-OAFA | (02h 39m 03.23s , -39d 42m 04.7s) | C | 40 | 18.9 | 1215 | 2025-09-10 03:35:58 | MASTER-OAFA | (02h 39m 03.16s , -39d 42m 03.1s) | C | 40 | 18.8 | 1261 | 2025-09-10 03:36:45 | MASTER-OAFA | (02h 39m 03.15s , -39d 42m 01.5s) | C | 40 | 18.8 | 1306 | 2025-09-10 03:37:30 | MASTER-OAFA | (02h 39m 03.08s , -39d 41m 59.9s) | C | 40 | 18.9 | 1352 | 2025-09-10 03:38:15 | MASTER-OAFA | (02h 39m 03.06s , -39d 41m 58.1s) | C | 40 | 18.9 | 1398 | 2025-09-10 03:39:01 | MASTER-OAFA | (02h 39m 03.03s , -39d 41m 56.4s) | C | 40 | 18.9 | 1443 | 2025-09-10 03:39:46 | MASTER-OAFA | (02h 39m 03.00s , -39d 41m 55.0s) | C | 40 | 18.9 | 1488 | 2025-09-10 03:40:32 | MASTER-OAFA | (02h 39m 02.97s , -39d 41m 53.5s) | C | 40 | 18.9 | 1535 | 2025-09-10 03:41:19 | MASTER-OAFA | (02h 39m 02.93s , -39d 41m 52.0s) | C | 40 | 18.9 | 1580 | 2025-09-10 03:42:04 | MASTER-OAFA | (02h 39m 02.89s , -39d 41m 50.3s) | C | 40 | 18.9 | 1626 | 2025-09-10 03:42:50 | MASTER-OAFA | (02h 39m 02.87s , -39d 41m 49.0s) | C | 40 | 18.9 | 8775 | 2025-09-10 05:41:58 | MASTER-OAFA | (02h 39m 14.92s , -39d 38m 15.4s) | C | 40 | 19.0 | 8820 | 2025-09-10 05:42:44 | MASTER-OAFA | (02h 39m 15.02s , -39d 38m 14.6s) | C | 40 | 19.0 | 8866 | 2025-09-10 05:43:29 | MASTER-OAFA | (02h 39m 15.10s , -39d 38m 13.5s) | C | 40 | 19.0 | 8912 | 2025-09-10 05:44:16 | MASTER-OAFA | (02h 39m 15.16s , -39d 38m 12.2s) | C | 40 | 19.0 | 8958 | 2025-09-10 05:45:01 | MASTER-OAFA | (02h 39m 15.23s , -39d 38m 11.0s) | C | 40 | 19.0 | 9003 | 2025-09-10 05:45:46 | MASTER-OAFA | (02h 39m 15.27s , -39d 38m 09.8s) | C | 40 | 19.1 | 9050 | 2025-09-10 05:46:34 | MASTER-OAFA | (02h 39m 15.35s , -39d 38m 08.4s) | C | 40 | 19.2 | 9096 | 2025-09-10 05:47:19 | MASTER-OAFA | (02h 39m 15.36s , -39d 38m 07.0s) | C | 40 | 19.2 | 9141 | 2025-09-10 05:48:05 | MASTER-OAFA | (02h 39m 15.41s , -39d 38m 05.9s) | C | 40 | 19.2 | 9187 | 2025-09-10 05:48:51 | MASTER-OAFA | (02h 39m 15.48s , -39d 38m 04.6s) | C | 40 | 19.1 | 9233 | 2025-09-10 05:49:36 | MASTER-OAFA | (02h 39m 15.55s , -39d 38m 03.0s) | C | 40 | 19.2 | 9278 | 2025-09-10 05:50:22 | MASTER-OAFA | (02h 39m 15.61s , -39d 38m 01.9s) | C | 40 | 19.3 | 9601 | 2025-09-10 05:55:35 | MASTER-OAFA | (02h 33m 49.69s , -39d 37m 50.4s) | C | 60 | 19.4 | 9677 | 2025-09-10 05:56:51 | MASTER-OAFA | (02h 33m 54.50s , -39d 38m 48.0s) | C | 60 | 19.3 | 9755 | 2025-09-10 05:58:09 | MASTER-OAFA | (02h 33m 49.60s , -39d 39m 45.9s) | C | 60 | 19.4 | 9831 | 2025-09-10 05:59:24 | MASTER-OAFA | (02h 44m 18.55s , -39d 39m 18.6s) | C | 60 | 19.5 | 9907 | 2025-09-10 06:00:40 | MASTER-OAFA | (02h 44m 16.33s , -39d 37m 58.7s) | C | 60 | 19.5 | 9991 | 2025-09-10 06:02:05 | MASTER-OAFA | (02h 44m 16.40s , -39d 39m 33.5s) | C | 60 | 19.5 | 12839 | 2025-09-10 06:49:33 | MASTER-OAFA | (02h 44m 22.49s , -39d 36m 17.7s) | C | 60 | 18.5 | 12914 | 2025-09-10 06:50:48 | MASTER-OAFA | (02h 44m 16.60s , -39d 37m 14.4s) | C | 60 | 18.5 | 12995 | 2025-09-10 06:52:08 | MASTER-OAFA | (02h 44m 16.65s , -39d 36m 12.0s) | C | 60 | 18.5 | 21335 | 2025-09-10 09:11:08 | MASTER-OAFA | (02h 34m 24.31s , -39d 47m 18.9s) | C | 60 | 18.1 | 21411 | 2025-09-10 09:12:25 | MASTER-OAFA | (02h 44m 52.99s , -39d 48m 13.6s) | C | 60 | 18.2 | 21650 | 2025-09-10 09:16:23 | MASTER-OAFA | (02h 34m 27.58s , -39d 47m 23.8s) | C | 60 | 18.0 | 21725 | 2025-09-10 09:17:39 | MASTER-OAFA | (02h 44m 51.45s , -39d 48m 38.3s) | C | 60 | 18.3 | 21885 | 2025-09-10 09:20:18 | MASTER-OAFA | (02h 34m 24.84s , -39d 48m 09.4s) | C | 60 | 18.0 | 23662 | 2025-09-10 09:49:55 | MASTER-OAFA | (02h 44m 54.42s , -39d 48m 19.8s) | C | 60 | 18.1 | 23738 | 2025-09-10 09:51:12 | MASTER-OAFA | (02h 44m 57.09s , -39d 46m 48.8s) | C | 60 | 18.0 | 23814 | 2025-09-10 09:52:27 | MASTER-OAFA | (02h 44m 52.46s , -39d 47m 38.5s) | C | 60 | 17.9 | 108092 | 2025-09-11 09:17:15 | MASTER-OAFA | (02h 34m 29.12s , -39d 47m 30.9s) | C | 40 | 19.6 | 108137 | 2025-09-11 09:18:01 | MASTER-OAFA | (02h 34m 29.19s , -39d 47m 30.2s) | C | 40 | 19.5 | 108183 | 2025-09-11 09:18:46 | MASTER-OAFA | (02h 34m 29.25s , -39d 47m 29.8s) | C | 40 | 19.5 | 108235 | 2025-09-11 09:19:39 | MASTER-OAFA | (02h 34m 29.29s , -39d 47m 29.2s) | C | 40 | 19.5 | 108281 | 2025-09-11 09:20:24 | MASTER-OAFA | (02h 34m 29.36s , -39d 47m 28.6s) | C | 40 | 19.5 | 108326 | 2025-09-11 09:21:10 | MASTER-OAFA | (02h 34m 29.44s , -39d 47m 28.0s) | C | 40 | 19.6 | 108378 | 2025-09-11 09:22:02 | MASTER-OAFA | (02h 34m 29.50s , -39d 47m 27.5s) | C | 40 | 19.5 | 108424 | 2025-09-11 09:22:48 | MASTER-OAFA | (02h 34m 29.55s , -39d 47m 27.0s) | C | 40 | 19.5 | 108469 | 2025-09-11 09:23:33 | MASTER-OAFA | (02h 34m 29.62s , -39d 47m 26.2s) | C | 40 | 19.5 | 108521 | 2025-09-11 09:24:24 | MASTER-OAFA | (02h 34m 29.66s , -39d 47m 25.8s) | C | 40 | 19.5 | 108567 | 2025-09-11 09:25:10 | MASTER-OAFA | (02h 34m 29.74s , -39d 47m 25.1s) | C | 40 | 19.6 | 108612 | 2025-09-11 09:25:56 | MASTER-OAFA | (02h 34m 29.81s , -39d 47m 24.6s) | C | 40 | 19.5 | 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/41789. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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