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[vsnet-grb-info 38523] GRB 250520A: Swift detection of a burst
by GCN Circulars 20 May '25

20 May '25

TITLE: GCN CIRCULAR NUMBER: 40491 SUBJECT: GRB 250520A: Swift detection of a burst DATE: 25/05/20 02:59:58 GMT FROM: K.L. Page at U Leicester <klp5(a)leicester.ac.uk> R. A. J. Eyles-Ferris (U Leicester), N. P. M. Kuin (UCL-MSSL), A. Y. Lien (U Tampa), M. J. Moss (GSFC) and K. L. Page (U Leicester) report on behalf of the Neil Gehrels Swift Observatory Team: At 02:42:16.84 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 250520A (trigger=1315630). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 282.268, -11.847 which is RA(J2000) = 18h 49m 04s Dec(J2000) = -11d 50' 49" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a short burst with a duration of about 1 sec. The peak count rate was ~10,000 counts/sec (15-350 keV), at ~0 sec after the trigger. The XRT began observing the field at 02:44:40.8 UT, 144.1 seconds after the BAT trigger. Using promptly downlinked data we find a fading, uncatalogued X-ray source located at RA, Dec 282.28588, -11.86811 which is equivalent to: RA(J2000) = 18h 49m 08.61s Dec(J2000) = -11d 52' 05.2" with an uncertainty of 3.6 arcseconds (radius, 90% containment). This location is 98 arcseconds from the BAT onboard position, within the BAT error circle. This position may be improved as more data are received; the latest position is available at https://www.swift.ac.uk/sper. A power-law fit to a spectrum formed from promptly downlinked event data gives a column density in excess of the Galactic value (3.68 x 10^21 cm^-2, Willingale et al. 2013), with an excess column of 8 (+6.16/-4.83) x 10^21 cm^-2 (90% confidence). UVOT took a finding chart exposure of 150 seconds with the White filter starting 148 seconds after the BAT trigger. No credible afterglow candidate has been found in the initial data products. The 2.7'x2.7' sub-image covers 100% of the XRT error circle. Because of the density of catalogued stars, further analysis is required to report an upper limit for any afterglow in the sub-image. The 8'x8' region for the list of sources generated on-board covers 100% of the XRT error circle. Because of the density of catalogued stars, further analysis is required to report an upper limit for any afterglow in the region. No correction has been made for the large, but uncertain, extinction expected. Burst Advocate for this burst is R. A. J. Eyles-Ferris (raje1 AT leicester.ac.uk). 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/40491. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38522] Swift GRB250520.11: Global MASTER-Net observations report
by GCN Circulars 20 May '25

20 May '25

TITLE: GCN CIRCULAR NUMBER: 40490 SUBJECT: Swift GRB250520.11: Global MASTER-Net observations report DATE: 25/05/20 02:56:51 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) was pointed to the Swift GRB250520.11 (trigger No 1315630,18h 49m 04.32s , -11d 50m 49.2s, R=0.05) errorbox 23 sec after notice time and 46 sec after trigger time at 2025-05-20 02:43:03 UT, with upper limit up to 17.0 mag. The observations began at zenith distance = 25 deg. The sun altitude is -33.7 deg. The galactic latitude b = -5 deg., longitude l = 22 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2875870 We obtain a following upper limits. Tmid-T0 | Site |Filt.| Expt. | Limit| Comment _________|_____________________|_____|_______|______|________ 52 | MASTER-SAAO | C | 10 | 16.3 | 80 | MASTER-SAAO | C | 10 | 16.3 | 115 | MASTER-SAAO | C | 20 | 16.4 | 159 | MASTER-SAAO | C | 30 | 16.7 | 213 | MASTER-SAAO | C | 40 | 16.7 | 277 | MASTER-SAAO | C | 50 | 16.7 | 351 | MASTER-SAAO | C | 60 | 17.0 | 430 | MASTER-SAAO | C | 60 | 16.9 | 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/40490. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38521] GRB 250516B: Insight-HXMT detection
by GCN Circulars 19 May '25

19 May '25

TITLE: GCN CIRCULAR NUMBER: 40489 SUBJECT: GRB 250516B: Insight-HXMT detection DATE: 25/05/19 12:37:22 GMT FROM: Chenwei Wang at IHEP <cwwang(a)ihep.ac.cn> Chen-Wei Wang, Shao-Lin Xiong, and Jin-Peng Zhang report on behalf of the Insight-HXMT team: At 2025-05-16T06:31:34.7 (T0), Insight-HXMT/HE detected the bright long burst GRB 250516B, which is also detected by GECAM-B (Wang et al., GCN #40469), NuSTAR (B. Grefenstette et al., GCN #40484) and Konus-Wind. The Insight-HXMT/HE light curve mainly consists of multiple pulses with a T90 of 39.6 +0.3/-0.2 s. The 1s peak rate, measured from T0+13.1 s, is 27175 cnts/sec. The total counts from this burst is 423316 counts. The HXMT/HE light curve can be found here: https://www.bursthub.cn//admin/static/hxmtgrb250516B.png All measurements above are made with the CsI detectors operating in the regular mode with the energy range of about 30-1000 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/40489. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38520] EP250427a/GRB250427A: VLA Detection of Radio Counterpart
by GCN Circulars 19 May '25

19 May '25

TITLE: GCN CIRCULAR NUMBER: 40488 SUBJECT: EP250427a/GRB250427A: VLA Detection of Radio Counterpart DATE: 25/05/19 03:14:19 GMT FROM: Tao An at SHAO, CAS <antao(a)shao.ac.cn> Tao An and Yuanqi Liu (Shanghai Astronomical Observatory) report on behalf of a large collaboration. We report the detection of a radio counterpart to the fast X-ray transient EP250427a, discovered by the Einstein Probe on 2025 April 27 (Wang et al., GCN 40257). EP250427a, also designated GRB250427A (Ravasio et al. GCN 40262), is a transient X-ray source notable for its rapid rise and decay in X-ray emission, peaking within minutes of detection. This behavior, combined with its potential association with a gamma-ray burst (GRB), suggests it may belong to a rare class of high-energy astrophysical phenomena. Initial follow-up observations in X-rays and optical wavelengths reported a faint, uncatalogued host galaxy at its position (Liu et al., GCN 40260), with subsequent spectroscopic observations confirming the host galaxy redshift of z=1.52 (Saccardi et al., GCN 40266). On 2025 May 5, at approximately UT 11:25 (mid-time of the observation), we conducted observations using the Karl G. Jansky Very Large Array (VLA) under DDT program VLA/25A-467. The observations were carried out at central frequencies of 6 GHz (C-band) and 10 GHz (X-band). We detected a radio source coincident with the position of EP250427a, with measured flux densities of 26 +/- 7 μJy at 6 GHz and 77 +/- 7 μJy at 10 GHz. These values yield an inverted radio spectrum with a spectral index \alpha ≈ 2.1 (where S \propto ν^\alpha), hinting at physical processes such as synchrotron self-absorption. The inverted spectrum is consistent with an early-time radio afterglow where the emission region is still compact. Continued VLA monitoring is planned to track the flux density and spectral evolution of the radio counterpart, which will help refine models of its emission mechanism and constrain the energetics of the event. We express our gratitude to the VLA TAC for approving the DDT proposal and to the VLA staff for their swift scheduling and support during these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/40488. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38519] GRB 250516A: Swift-BAT refined analysis
by GCN Circulars 19 May '25

19 May '25

TITLE: GCN CIRCULAR NUMBER: 40487 SUBJECT: GRB 250516A: Swift-BAT refined analysis DATE: 25/05/19 03:04:35 GMT FROM: Amy <yarleen(a)gmail.com> T. Sakamoto (AGU), S. D. Barthelmy (GSFC), A. P. Beardmore (U Leicester), R. Gupta (GSFC), H. A. Krimm (NSF), S. Laha (GSFC/UMBC), A. Y. Lien (U Tampa), C. B. Markwardt (GSFC), M. J. Moss (GSFC), D. M. Palmer (LANL), T. Parsotan (GSFC), D. Sadaula (GSFC/UMBC), (i.e. the Swift-BAT team): Using the data set from T-240 to T+963 sec from the recent telemetry downlink, we report further analysis of BAT GRB 250516A (trigger #1314210) (Beardmore et al., GCN Circ. 40467). The BAT ground-calculated position is RA, Dec = 334.612, -9.120 deg which is RA(J2000) = 22h 18m 26.8s Dec(J2000) = -09d 07' 11.9" with an uncertainty of 1.1 arcmin, (radius, sys+stat, 90% containment). The partial coding was 61%. The mask-weighted light curve shows a multi-peaked structure that starts at ~T-20 s and ends at ~T+23 s. The highest peak occurs at ~T+20 s. T90 (15-350 keV) is 30.04 +- 6.01 sec (estimated error including systematics). The time-averaged spectrum from T-19.96 to T+22.70 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.69 +- 0.08. The fluence in the 15-150 keV band is 2.3 +- 0.1 x 10^-06 erg/cm2. The 1-sec peak photon flux measured from T+19.39 sec in the 15-150 keV band is 3.8 +- 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/1314210 View this GCN Circular online at https://gcn.nasa.gov/circulars/40487. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38518] GRB 250516A: COLIBRÍ optical upper limit
by GCN Circulars 18 May '25

18 May '25

TITLE: GCN CIRCULAR NUMBER: 40486 SUBJECT: GRB 250516A: COLIBRÍ optical upper limit DATE: 25/05/18 16:00:54 GMT FROM: Rosa L. Becerra at Tor Vergata, Roma <rosa.becerra(a)roma2.infn.it> Francis Fortin (IRAP), Kin Ocelotl López (UNAM), Rosa L. Becerra (U Roma), Alan M. Watson (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Jean-Luc Atteia (IRAP), Fredd Alvarez (UNAM), Dalya Akl (AUS), Camila Angulo (UNAM), Sarah Antier (OCA), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Leonardo García García (UNAM), Noémie Globus (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 GRB 250516A (Fermi GBM team GCN Circ. 40466; Beardmore et al., GCN Circ. 40467; Frederiks et al., GCN Circ. 40485) using the DDRAGO wide-field imager on the COLIBRÍ telescope. We observed from 2025-05-18 09:59 to 11:20 UTC (from 43.4 to 44.8 hours after the trigger) and obtained 64 minutes of exposure in the r filter. The data were reduced and coadded with the COLIBRÍ pipeline and analysed with STDWeb/STDPipe (Karpov 2025). The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction. In the stacked image, we do not detect any new source at the XRT source position (Evans et al., GCN Circ. 40468) down to the following 3-sigma limit: r > 22.08 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/40486. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38517] Konus-Wind detection of GRB 250516A
by GCN Circulars 18 May '25

18 May '25

TITLE: GCN CIRCULAR NUMBER: 40485 SUBJECT: Konus-Wind detection of GRB 250516A DATE: 25/05/18 13:53:49 GMT FROM: Dmitry Frederiks at Ioffe Institute <fred(a)mail.ioffe.ru> D. Frederiks, A.Lysenko, A. Ridnaya, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report The long GRB 250516A (Fermi GBM detection: Fermi GBM team, GCN 40466; Mukherjee & Meegan, GCN 40473; Swift detection: Beardmore et al., GCN 40467) was detected by Konus-Wind (KW) in the waiting mode. A Bayesian block analysis of the KW waiting mode data in the 20-400 keV band reveals a ~11 sigma count-rate increase in the interval from T0-2.757 s to T0+23.739 s where T0 = 14:35:29 UT. The KW light curve of this burst is available at http://www.ioffe.ru/LEA/GRBs/GRB250516A/ Modeling the time-integrated spectrum of the burst by a power law with exponential cutoff (CPL) model dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) yields alpha = -1.21 (-0.10, + 0.10) and Ep = 164(-9,+10) keV. Modelling the spectrum near the peak count rate (T0+3.131 s to T0+9.019 s) by a CPL function yields alpha = -1.35 (-0.10, + 0.11) and Ep = 403(-53,+82) keV. In the 20 keV -10 MeV band, standard for the KW analysis, the burst fluence is (4.41 ± 1.33)x10^-6 erg/cm^2 and the 2.944 s peak energy flux, measured from T0+6.075 s, is (5.85 ± 0.42)x10^-7 erg/cm^2/s. All the quoted errors are estimated at the 68% confidence level. All the presented results are preliminary. View this GCN Circular online at https://gcn.nasa.gov/circulars/40485. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38516] GRB 250516B: NuSTAR Detection of the Prompt Emission
by GCN Circulars 17 May '25

17 May '25

TITLE: GCN CIRCULAR NUMBER: 40484 SUBJECT: GRB 250516B: NuSTAR Detection of the Prompt Emission DATE: 25/05/17 19:08:14 GMT FROM: Brian Grefenstette at Caltech/NuSTAR <bwgref(a)srl.caltech.edu> B. Grefenstette (Caltech) reports 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 GRB 250516B in both the NuSTAR CsI anti-coincidence shields and in the CdZnTe detectors. 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 2025-05-16 06:31:39 with a resolution ~5-seconds. This is consistent with the GECAM-B reported time of 2025-05-16T06:31:34.7 (Wang et al., GCN circ. 40469). The GRB is a broad burst with multiples peaks. The brightest has a peak count rates in the anti-coincidence shields near 4,000 cps over a baseline of ~1,000 cps. The burst is also clearly seen in the CdZnTe detectors. Discovery report and a preliminary lightcurves for this GRB can be found here: https://nustarsoc.caltech.edu/NuSTAR_Public/grbs/reports/2025/250516B/ 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/40484. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38515] EP-WXT trigger (ID: 01709176312): a new X-ray outburst of HMXB RX J0111.2-7317
by GCN Circulars 17 May '25

17 May '25

TITLE: GCN CIRCULAR NUMBER: 40483 SUBJECT: EP-WXT trigger (ID: 01709176312): a new X-ray outburst of HMXB RX J0111.2-7317 DATE: 25/05/17 15:40:03 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Q. C. Liu (THU), X.-Y. Zhou (PRIC), Y.-H. I. Yin (NJU) and C. C. Jin (NAO, CAS) report on behalf of the Einstein Probe team: We report on the detection of a new X-ray outburst of the High Mass X-ray Binary (HMXB) RX J0111.2-7317 by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission. The burst triggered EP-WXT (ID: 01709176312) at 2025-05-16T19:26:03 (UTC). The emission lasted for around 100 min. The WXT position of the source, inferred from the onground analysis, is R.A. = 17.759 deg, DEC = -73.279 deg (J2000) with an uncertainty of 2.5 arcmin in radius (90% C.L. statistical and systematic). The averaged WXT spectrum in 0.5-4 keV can be fitted by an absorbed power law model a Galactic hydrogen column density of 4.9 x 10^21 cm^-2 and a photon index of 3.10 (+/-0.43). The average unabsorbed 0.5-4 keV flux is 1.3 (-2.0, +2.0) x 10^-10 erg/cm^2/s. Following the WXT trigger, a follow-up observation with the Follow-up X-ray Telescope (FXT) was performed automatically. The FXT observation started at 2025-05-16T19:26:35 (UTC), around 30 seconds after the trigger. The analysis of the data, with an exposure of 2 ks, reveals a detection of an X-ray source at RA = 17.7851 deg, Dec = -73.2799 deg (J2000) with an uncertainty of 10 arcsec in radius (90% C.L. statistical and systematic). This position is consistent with the known HMXB RX J0111.2-7317, confirming the WXT detection as the outburst of this X-ray source. The averaged FXT spectrum in 0.5-10 keV can be roughly fitted by an absorbed power law model a Galactic hydrogen column density of 4.9 x 10^21 cm^-2 and a photon index of 1.86 (+/-0.01). The average unabsorbed 0.5-10 keV flux is 1.48 (-0.02, +0.02) x 10^-10 erg/cm^2/s, which is consistent with the flux detected by the WXT. The X-ray outburst was previously detected by WXT at 2025-05-13T14:15:40 (UTC). The observed flux is around 3.26 x 10^-11 erg/cm^2/s, consistent with the following WXT and FXT observations. More 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/40483. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38514] Fermi GRB 250516A: Global MASTER-Net observations report
by GCN Circulars 17 May '25

17 May '25

TITLE: GCN CIRCULAR NUMBER: 40482 SUBJECT: Fermi GRB 250516A: Global MASTER-Net observations report DATE: 25/05/17 13:16:04 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 250516A ( Fermi GBM team, GCN 40466) errorbox 53236 sec after notice time and 53273 sec after trigger time at 2025-05-17 05:23:23 UT, with upper limit up to 19.8 mag. The observations began at zenith distance = 81 deg. The sun altitude is -73.4 deg. The galactic latitude b = -43 deg., longitude l = 63 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2872281 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 53354 | 2025-05-17 05:23:23 | MASTER-OAFA | (22h 08m 57.57s , -09d 53m 16.4s) | C | 160 | 16.3 | 54587 | 2025-05-17 05:43:56 | MASTER-OAFA | (22h 08m 53.80s , -09d 49m 35.9s) | C | 160 | 16.6 | 54724 | 2025-05-17 05:47:13 | MASTER-OAFA | (22h 08m 48.08s , -09d 50m 58.9s) | C | 40 | 16.7 | 55010 | 2025-05-17 05:50:59 | MASTER-OAFA | (22h 09m 00.15s , -09d 50m 43.3s) | C | 160 | 16.9 | 55020 | 2025-05-17 05:50:59 | MASTER-OAFA | (22h 19m 10.53s , -09d 28m 33.4s) | C | 180 | 15.5 | 55206 | 2025-05-17 05:54:15 | MASTER-OAFA | (22h 08m 57.96s , -09d 49m 01.8s) | C | 160 | 17.0 | 55216 | 2025-05-17 05:54:15 | MASTER-OAFA | (22h 19m 08.28s , -09d 26m 54.9s) | C | 180 | 16.0 | 55401 | 2025-05-17 05:57:30 | MASTER-OAFA | (22h 08m 58.20s , -09d 49m 52.9s) | C | 160 | 17.0 | 55411 | 2025-05-17 05:57:30 | MASTER-OAFA | (22h 19m 08.56s , -09d 27m 47.0s) | C | 180 | 16.7 | 55597 | 2025-05-17 06:00:46 | MASTER-OAFA | (22h 09m 01.12s , -09d 48m 33.7s) | C | 160 | 17.1 | 55607 | 2025-05-17 06:00:46 | MASTER-OAFA | (22h 19m 11.35s , -09d 26m 29.4s) | C | 180 | 16.9 | 56557 | 2025-05-17 06:16:46 | MASTER-OAFA | (22h 08m 55.08s , -09d 48m 15.8s) | C | 160 | 17.1 | 56568 | 2025-05-17 06:16:46 | MASTER-OAFA | (22h 19m 06.24s , -09d 26m 09.9s) | C | 180 | 17.9 | 56752 | 2025-05-17 06:20:01 | MASTER-OAFA | (22h 08m 57.37s , -09d 46m 58.3s) | C | 160 | 17.3 | 56763 | 2025-05-17 06:20:02 | MASTER-OAFA | (22h 19m 08.29s , -09d 24m 56.6s) | C | 180 | 18.0 | 56946 | 2025-05-17 06:23:15 | MASTER-OAFA | (22h 09m 01.40s , -09d 47m 45.6s) | C | 160 | 17.4 | 56956 | 2025-05-17 06:23:15 | MASTER-OAFA | (22h 19m 12.42s , -09d 25m 45.4s) | C | 180 | 18.3 | 57850 | 2025-05-17 06:39:19 | MASTER-OAFA | (22h 08m 51.04s , -09d 48m 32.1s) | C | 40 | 17.1 | 57860 | 2025-05-17 06:39:19 | MASTER-OAFA | (22h 18m 01.41s , -09d 25m 06.5s) | C | 60 | 18.3 | 58215 | 2025-05-17 06:44:23 | MASTER-OAFA | (22h 09m 03.18s , -09d 45m 55.1s) | C | 160 | 17.5 | 58225 | 2025-05-17 06:44:24 | MASTER-OAFA | (22h 19m 14.38s , -09d 23m 59.1s) | C | 180 | 18.8 | 59041 | 2025-05-17 06:59:10 | MASTER-OAFA | (22h 08m 45.76s , -09d 46m 30.8s) | C | 40 | 17.1 | 59051 | 2025-05-17 06:59:10 | MASTER-OAFA | (22h 17m 56.74s , -09d 23m 08.5s) | C | 60 | 18.5 | 59424 | 2025-05-17 07:04:33 | MASTER-OAFA | (22h 08m 56.48s , -09d 46m 31.6s) | C | 160 | 17.5 | 59434 | 2025-05-17 07:04:33 | MASTER-OAFA | (22h 19m 08.49s , -09d 24m 38.0s) | C | 180 | 18.9 | 60168 | 2025-05-17 07:17:57 | MASTER-OAFA | (22h 08m 45.17s , -09d 46m 41.0s) | C | 40 | 17.1 | 60179 | 2025-05-17 07:17:57 | MASTER-OAFA | (22h 17m 56.70s , -09d 23m 17.5s) | C | 60 | 18.7 | 60363 | 2025-05-17 07:21:11 | MASTER-OAFA | (22h 08m 48.12s , -09d 44m 50.5s) | C | 40 | 17.3 | 60373 | 2025-05-17 07:21:12 | MASTER-OAFA | (22h 17m 59.64s , -09d 21m 30.3s) | C | 60 | 18.9 | 60616 | 2025-05-17 07:24:25 | MASTER-OAFA | (22h 09m 03.10s , -09d 43m 57.6s) | C | 160 | 17.8 | 60626 | 2025-05-17 07:24:25 | MASTER-OAFA | (22h 19m 14.88s , -09d 21m 57.0s) | C | 180 | 19.1 | 62075 | 2025-05-17 07:48:44 | MASTER-OAFA | (22h 08m 55.13s , -09d 42m 54.6s) | C | 160 | 17.7 | 62086 | 2025-05-17 07:48:44 | MASTER-OAFA | (22h 19m 08.48s , -09d 20m 53.2s) | C | 180 | 19.3 | 62214 | 2025-05-17 07:52:02 | MASTER-OAFA | (22h 08m 49.30s , -09d 44m 23.1s) | C | 40 | 17.4 | 62224 | 2025-05-17 07:52:03 | MASTER-OAFA | (22h 18m 01.84s , -09d 20m 58.6s) | C | 60 | 19.2 | 63302 | 2025-05-17 08:09:10 | MASTER-OAFA | (22h 08m 57.42s , -09d 43m 55.7s) | C | 160 | 18.0 | 63312 | 2025-05-17 08:09:11 | MASTER-OAFA | (22h 19m 11.59s , -09d 21m 56.1s) | C | 180 | 19.6 | 65610 | 2025-05-17 08:47:39 | MASTER-OAFA | (22h 08m 55.02s , -09d 41m 06.6s) | C | 160 | 18.1 | 65620 | 2025-05-17 08:47:39 | MASTER-OAFA | (22h 19m 09.74s , -09d 19m 09.9s) | C | 180 | 19.6 | 66945 | 2025-05-17 09:09:53 | MASTER-OAFA | (22h 08m 56.20s , -09d 42m 17.9s) | C | 160 | 18.2 | 66955 | 2025-05-17 09:09:54 | MASTER-OAFA | (22h 19m 12.01s , -09d 20m 14.9s) | C | 180 | 19.8 | 68016 | 2025-05-17 09:28:45 | MASTER-OAFA | (21h 54m 48.23s , -07d 54m 13.2s) | C | 40 | 17.7 | 68155 | 2025-05-17 09:30:04 | MASTER-OAFA | (22h 27m 36.59s , -08d 43m 27.0s) | C | 160 | 18.4 | 68165 | 2025-05-17 09:30:04 | MASTER-OAFA | (22h 17m 17.92s , -09d 03m 28.4s) | C | 180 | 19.7 | 68957 | 2025-05-17 09:44:25 | MASTER-OAFA | (21h 54m 46.25s , -07d 53m 07.2s) | C | 40 | 17.7 | 69276 | 2025-05-17 09:49:45 | MASTER-OAFA | (22h 27m 06.28s , +01d 35m 10.8s) | C | 40 | 17.4 | 69286 | 2025-05-17 09:49:45 | MASTER-OAFA | (22h 17m 55.04s , +01d 12m 56.3s) | C | 60 | 18.7 | 69415 | 2025-05-17 09:51:03 | MASTER-OAFA | (22h 27m 35.48s , -08d 42m 28.0s) | C | 160 | 18.6 | 69425 | 2025-05-17 09:51:04 | MASTER-OAFA | (22h 17m 16.20s , -09d 02m 35.8s) | C | 180 | 19.7 | 69553 | 2025-05-17 09:54:21 | MASTER-OAFA | (22h 26m 50.43s , -00d 18m 25.4s) | C | 40 | 17.5 | 69563 | 2025-05-17 09:54:22 | MASTER-OAFA | (22h 17m 38.98s , -00d 40m 37.2s) | C | 60 | 19.2 | 69631 | 2025-05-17 09:55:39 | MASTER-OAFA | (22h 11m 55.19s , +01d 37m 25.6s) | C | 40 | 17.4 | 69641 | 2025-05-17 09:55:40 | MASTER-OAFA | (22h 02m 43.70s , +01d 15m 10.5s) | C | 60 | 19.4 | 69706 | 2025-05-17 09:56:55 | MASTER-OAFA | (22h 28m 42.02s , +03d 30m 10.0s) | C | 40 | 17.0 | 69716 | 2025-05-17 09:56:55 | MASTER-OAFA | (22h 19m 30.05s , +03d 07m 48.2s) | C | 60 | 18.1 | 69785 | 2025-05-17 09:58:14 | MASTER-OAFA | (22h 42m 12.03s , +01d 36m 43.5s) | C | 40 | 17.9 | 69795 | 2025-05-17 09:58:14 | MASTER-OAFA | (22h 33m 00.73s , +01d 14m 23.6s) | C | 60 | 19.3 | 69865 | 2025-05-17 09:59:33 | MASTER-OAFA | (22h 43m 22.31s , -02d 12m 22.6s) | C | 40 | 17.8 | 69875 | 2025-05-17 09:59:34 | MASTER-OAFA | (22h 34m 10.40s , -02d 34m 34.0s) | C | 60 | 19.3 | 69944 | 2025-05-17 10:00:52 | MASTER-OAFA | (22h 27m 01.19s , +01d 35m 18.5s) | C | 40 | 17.4 | 69954 | 2025-05-17 10:00:53 | MASTER-OAFA | (22h 17m 49.81s , +01d 12m 59.9s) | C | 60 | 18.8 | 70024 | 2025-05-17 10:02:12 | MASTER-OAFA | (22h 30m 55.45s , -04d 06m 35.7s) | C | 40 | 17.7 | 70034 | 2025-05-17 10:02:13 | MASTER-OAFA | (22h 21m 42.26s , -04d 28m 41.7s) | C | 60 | 19.2 | 70103 | 2025-05-17 10:03:31 | MASTER-OAFA | (22h 12m 53.62s , -02d 10m 32.8s) | C | 40 | 17.7 | 70113 | 2025-05-17 10:03:32 | MASTER-OAFA | (22h 03m 41.57s , -02d 32m 40.4s) | C | 60 | 19.3 | 70179 | 2025-05-17 10:04:48 | MASTER-OAFA | (22h 26m 50.63s , -00d 18m 22.6s) | C | 40 | 17.4 | 70189 | 2025-05-17 10:04:48 | MASTER-OAFA | (22h 17m 39.16s , -00d 40m 35.4s) | C | 60 | 19.0 | 70258 | 2025-05-17 10:06:07 | MASTER-OAFA | (22h 11m 54.89s , +01d 37m 38.1s) | C | 40 | 17.4 | 70268 | 2025-05-17 10:06:07 | MASTER-OAFA | (22h 02m 43.38s , +01d 15m 22.1s) | C | 60 | 19.3 | 70335 | 2025-05-17 10:07:24 | MASTER-OAFA | (22h 28m 43.22s , +03d 30m 23.6s) | C | 40 | 17.0 | 70346 | 2025-05-17 10:07:24 | MASTER-OAFA | (22h 19m 31.24s , +03d 08m 01.5s) | C | 60 | 18.1 | 70413 | 2025-05-17 10:08:42 | MASTER-OAFA | (22h 42m 12.23s , +01d 36m 55.4s) | C | 40 | 17.9 | 70423 | 2025-05-17 10:08:42 | MASTER-OAFA | (22h 33m 00.93s , +01d 14m 35.7s) | C | 60 | 19.3 | 70490 | 2025-05-17 10:09:59 | MASTER-OAFA | (22h 43m 21.90s , -02d 12m 10.0s) | C | 40 | 17.6 | 70500 | 2025-05-17 10:09:59 | MASTER-OAFA | (22h 34m 09.98s , -02d 34m 21.8s) | C | 60 | 19.1 | 70629 | 2025-05-17 10:11:18 | MASTER-OAFA | (22h 27m 33.04s , -08d 43m 51.9s) | C | 160 | 18.5 | 70639 | 2025-05-17 10:11:18 | MASTER-OAFA | (22h 17m 13.64s , -09d 04m 01.9s) | C | 180 | 19.6 | 70767 | 2025-05-17 10:14:36 | MASTER-OAFA | (22h 27m 07.09s , +01d 35m 50.2s) | C | 40 | 17.4 | 70777 | 2025-05-17 10:14:36 | MASTER-OAFA | (22h 17m 55.62s , +01d 13m 33.1s) | C | 60 | 18.7 | 70845 | 2025-05-17 10:15:54 | MASTER-OAFA | (22h 30m 52.15s , -04d 04m 48.9s) | C | 40 | 17.5 | 70856 | 2025-05-17 10:15:54 | MASTER-OAFA | (22h 21m 38.89s , -04d 26m 54.1s) | C | 60 | 19.0 | 70923 | 2025-05-17 10:17:12 | MASTER-OAFA | (22h 12m 53.74s , -02d 11m 39.7s) | C | 40 | 17.6 | 70933 | 2025-05-17 10:17:12 | MASTER-OAFA | (22h 03m 41.60s , -02d 33m 46.9s) | C | 60 | 19.3 | 70999 | 2025-05-17 10:18:28 | MASTER-OAFA | (22h 26m 52.97s , -00d 16m 47.4s) | C | 40 | 17.5 | 71009 | 2025-05-17 10:18:28 | MASTER-OAFA | (22h 17m 41.41s , -00d 38m 59.6s) | C | 60 | 19.0 | 71076 | 2025-05-17 10:19:44 | MASTER-OAFA | (22h 11m 47.30s , +01d 37m 17.4s) | C | 40 | 17.4 | 71086 | 2025-05-17 10:19:45 | MASTER-OAFA | (22h 02m 35.75s , +01d 15m 02.1s) | C | 60 | 19.0 | 71153 | 2025-05-17 10:21:02 | MASTER-OAFA | (22h 28m 42.63s , +03d 31m 39.9s) | C | 40 | 16.9 | 71164 | 2025-05-17 10:21:02 | MASTER-OAFA | (22h 19m 30.49s , +03d 09m 19.0s) | C | 60 | 17.9 | 71231 | 2025-05-17 10:22:20 | MASTER-OAFA | (22h 42m 19.67s , +01d 36m 09.6s) | C | 40 | 17.5 | 71241 | 2025-05-17 10:22:20 | MASTER-OAFA | (22h 33m 08.20s , +01d 13m 51.0s) | C | 60 | 18.7 | 71309 | 2025-05-17 10:23:38 | MASTER-OAFA | (22h 43m 15.76s , -02d 12m 56.3s) | C | 40 | 17.4 | 71319 | 2025-05-17 10:23:38 | MASTER-OAFA | (22h 34m 03.65s , -02d 35m 05.9s) | C | 60 | 18.8 | 71386 | 2025-05-17 10:24:55 | MASTER-OAFA | (22h 27m 07.17s , +01d 36m 13.3s) | C | 40 | 16.8 | 71396 | 2025-05-17 10:24:55 | MASTER-OAFA | (22h 17m 55.54s , +01d 13m 57.3s) | C | 60 | 18.3 | 71464 | 2025-05-17 10:26:13 | MASTER-OAFA | (22h 30m 52.43s , -04d 04m 36.5s) | C | 40 | 17.1 | 71475 | 2025-05-17 10:26:13 | MASTER-OAFA | (22h 21m 38.98s , -04d 26m 39.6s) | C | 60 | 18.5 | 71542 | 2025-05-17 10:27:31 | MASTER-OAFA | (22h 12m 53.84s , -02d 11m 34.0s) | C | 40 | 17.1 | 71552 | 2025-05-17 10:27:31 | MASTER-OAFA | (22h 03m 41.51s , -02d 33m 39.0s) | C | 60 | 18.5 | 71620 | 2025-05-17 10:28:49 | MASTER-OAFA | (22h 26m 53.05s , -00d 16m 22.4s) | C | 40 | 16.7 | 71631 | 2025-05-17 10:28:49 | MASTER-OAFA | (22h 17m 41.27s , -00d 38m 32.2s) | C | 60 | 18.3 | 71697 | 2025-05-17 10:30:06 | MASTER-OAFA | (22h 11m 49.08s , +01d 37m 28.1s) | C | 40 | 16.6 | 71708 | 2025-05-17 10:30:06 | MASTER-OAFA | (22h 02m 37.28s , +01d 15m 16.2s) | C | 60 | 18.3 | 71836 | 2025-05-17 10:31:25 | MASTER-OAFA | (22h 27m 34.11s , -08d 41m 29.1s) | C | 160 | 17.4 | 71974 | 2025-05-17 10:34:43 | MASTER-OAFA | (22h 28m 49.55s , +03d 30m 54.7s) | C | 40 | 15.9 | 72050 | 2025-05-17 10:35:59 | MASTER-OAFA | (22h 42m 11.99s , +01d 35m 23.8s) | C | 40 | 16.2 | 72127 | 2025-05-17 10:37:16 | MASTER-OAFA | (22h 43m 23.70s , -02d 12m 28.1s) | C | 40 | 16.0 | 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/40482. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38513] GRB 250515A: Swift-XRT observations
by GCN Circulars 17 May '25

17 May '25

TITLE: GCN CIRCULAR NUMBER: 40481 SUBJECT: GRB 250515A: Swift-XRT observations DATE: 25/05/17 08:43:22 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> M. Capalbi (INAF-IASFPA), M. Perri (SSDC & INAF-OAR), V. D'Elia (SSDC & INAF-OAR), D.N. Burrows (PSU), M.A. Williams (PSU), S. Dichiara (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester) 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 250515A, centred on the location of GOTO25cqo (GCN 40464) collecting 4.5 ks of Photon Counting (PC) mode data between T0+88.8 ks and T0+117.8 ks. No X-ray sources have been detected within the estimated 3-sigma GOTO error region (4.9 arcsec). The 3-sigma upper limit in the field ranges from ~0.002 to ~0.003 ct s^-1, corresponding to a 0.3-10 keV observed flux of 9.2e-14 to 1.4e-13 erg cm^-2 s^-1 (assuming a typical GRB spectrum). GOTO25cqo has since been classified as a type Ia supernova. 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/00021829. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/40481. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38512] GRB 250515A: NOT classification of GOTO25cqo as a type-Ia SN
by GCN Circulars 17 May '25

17 May '25

TITLE: GCN CIRCULAR NUMBER: 40480 SUBJECT: GRB 250515A: NOT classification of GOTO25cqo as a type-Ia SN DATE: 25/05/17 08:32:02 GMT FROM: Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani(a)nbi.ku.dk> A. Martin-Carrillo (UCD), Z. P. Zhu (NAOC), L. Izzo (INAF/OACN and DARK/NBI), D. B. Malesani (DAWN/NBI and Radboud), B. P. Gompertz (U. Birmingham), G. Corcoran (UCD), R. Rautio (Univ. Oulu), report on behalf of a larger collaboration. We observed the position of GOTO25cqo (Gompertz et al., GCN 40464), a candidate optical counterpart to GRB 250515A (Fermi GBM team, GCN 40462), using the ALFOSC camera mounted on the Nordic Optical Telescope (NOT). We obtained exposures in the SDSS r band (3x300 s) starting at 23:44:29 UT on 2025-05-16 (27 hours after the Fermi trigger). The candidate is detected in single exposures with an AB magnitude of r = 20.18 +/- 0.02, calibrated against nearby Pan-STARRS stars. We further obtained 4x600 s of spectroscopic observations. The flux-calibrated spectrum shows features not consistent with typical GRB afterglows. Using SNID (Blondin & Tonry 2007, doi:10.1086/520494), the spectrum matches well several normal rising type-Ia supernovae at z = 0.18 +/- 0.01. This excludes the association of GOTO25cqo with GRB 250515A, as already suggested by Xin et al. (GCN 40474) and Lopez et al. (GCN 40478). The slit was oriented so to cover the bright galaxy 5.3” NW of GOTO25cqo. We detect several emission lines which we identify Halpha, Hbeta, [O III] and [O II] at a common redshift of z = 0.169. With a 15 kpc projected separation, this galaxy is thus a plausible host of GOTO25cqo. We acknowledge excellent support from the NOT staff, in particular Joonas Viuho and Amanda Djupvik. View this GCN Circular online at https://gcn.nasa.gov/circulars/40480. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38511] Fermi Gamma-ray Burst Monitor trigger 769160489/250517320 is not a GRB
by GCN Circulars 17 May '25

17 May '25

TITLE: GCN CIRCULAR NUMBER: 40479 SUBJECT: Fermi Gamma-ray Burst Monitor trigger 769160489/250517320 is not a GRB DATE: 25/05/17 08:24:02 GMT FROM: A. Holzmann Airasca at University of Trento and INFN Bari <a.holzmannairasca(a)unitn.it> A. Holzmann Airasca (UniTrento and INFN Bari) reports on behalf of the Fermi Gamma-ray Burst Monitor Team: "The Fermi Gamma-ray Burst Monitor (GBM) trigger 769160489/250517320 at 07:41:24.32 UT on 17 May 2025, tentatively classified as a GRB, is in fact not due to a GRB. This trigger is likely due to local particles." View this GCN Circular online at https://gcn.nasa.gov/circulars/40479. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38510] GRB 250515A:COLIBRÍ optical observations of the GOTO candidate
by GCN Circulars 17 May '25

17 May '25

TITLE: GCN CIRCULAR NUMBER: 40478 SUBJECT: GRB 250515A:COLIBRÍ optical observations of the GOTO candidate DATE: 25/05/17 06:16:42 GMT FROM: Alan Watson at UNAM <alan(a)astro.unam.mx> Kin Ocelotl López (UNAM), Alan M. Watson (UNAM), Rosa L. Becerra (U Roma), Benjamin Schneider (LAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Fredd Alvarez (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (AUS), Sarah Antier (OCA), Nathaniel R. Butler (ASU) , Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Noémie Globus (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), and Antonio de Ugarte Postigo (LAM): We imaged the field of the GOTO candidate afterglow (Gompertz et al., GCN Circ. 40464) of the Fermi GRB 250515A (Fermi GBM team., GCN Circ. 40462) using the DDRAGO wide-field imager on the COLIBRÍ telescope. We observed from 2025-05-17 03:23 to 05:27 UTC (median epoch 1.30 days after the trigger) and obtained 32 minutes of exposure in the i filter and 3 minutes in each of the g and r 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 detected the optical candidate at preliminary magnitudes of: g = 20.31 +/- 0.03 r = 20.24 +/- 0.04 i = 20.45 +/- 0.03 This source was also detected by SVOM/VT (Xin et al., GCN Circ. 40474) and Mephisto (Zhang et al., GCN Circ. 40476). Our magnitudes are similar in g, fainter in r, and brighter in i than those reported at 0.71 days by Zhang et al. (GCN Circ. 40746), and these changes are not obviously compatible with the temporal evolution of a GRB afterglow after about 1 day. 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/40478. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38509] Swift GRB 250516A: Global MASTER-Net observations report
by GCN Circulars 17 May '25

17 May '25

TITLE: GCN CIRCULAR NUMBER: 40477 SUBJECT: Swift GRB 250516A: Global MASTER-Net observations report DATE: 25/05/17 05:58:24 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 Swift GRB 250516A ( A. P. Beardmore et al., GCN 40467) errorbox 54907 sec after notice time and 54930 sec after trigger time at 2025-05-17 05:50:59 UT, with upper limit up to 15.5 mag. The observations began at zenith distance = 77 deg. The sun altitude is -68.5 deg. The galactic latitude b = -50 deg., longitude l = 53 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2872228 We obtain a following upper limits. Tmid-T0 | Site |Filt.| Expt. | Limit| Comment _________|_____________________|_____|_______|______|________ 55020 | MASTER-OAFA | C | 180 | 15.5 | 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/40477. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38508] GRB 250515A: 1.6m Mephisto optical detection
by GCN Circulars 17 May '25

17 May '25

TITLE: GCN CIRCULAR NUMBER: 40476 SUBJECT: GRB 250515A: 1.6m Mephisto optical detection DATE: 25/05/17 05:06:22 GMT FROM: zhjh(a)nao.cas.cn Jinghua Zhang, Yu Pan, Xiangkun Liu, Yiheng Xie, Guowang Du, Yuan Fang, Xinlei Chen, Xingzhu Zou, Helong Guo, Xufeng Zhu, Tao Wang, Brajesh Kumar, Xinzhong Er, Yuanpei Yang, Xiaowei Liu (SWIFAR, YNU) report on behalf of Mephisto Team: We conducted simultaneous multi-band photometric observations of the optical candidate of the likely short GRB 250515A (Fermi GBM team, GCN 40462) with the 1.6m Multi-channel Photometric Survey Telescope (Mephisto) of Yunnan University, located at the Lijiang Observatory. Mephisto was triggered ~17 hours post-alert and commenced observations starting from 13:47:01 UTC 2025-05-16 in moderate sky conditions. Multiple frames across uvgriz bands were acquired. The optical candidate (B. P. Gompertz et al., GCN 40464; Xin et al., GCN40474) was clearly detected in the stacked images of g and r bands while marginally detected in the u, v, i, z -bands. The preliminary photometry (AB magnitude system) are listed below: | Time-Mid (2025-05-16 UT) | Filter | Exposure | Mag | Mag Err | | 15:02:22 | u | 300sec*3 | 21.17 | 0.27 | | 13:54:44 | v | 300sec*3 | 21.46 | 0.47 | | 15:02:22 | g | 300sec*3 | 20.21 | 0.07 | | 13:54:44 | r | 300sec*3 | 19.91 | 0.08 | | 15:02:22 | i | 300sec*3 | 20.74 | 0.20 | | 13:54:44 | z | 300sec*3 | 20.22 | 0.47 | ------------------------------------------------------------------------------------------------------- Mephisto (Multi-channel Photometric Survey Telescope) is a 1.6-m wide-field multi-channel telescope, the first of its type in the world, capable of imaging the same field of view in three optical bands simultaneously. It provides real-time, high-quality colors of stellar objects. The on-site telescope assemblage and commissioning were carried out in September 2022. The first light in all three channels was achieved on 2023 December 21. ------------------------------------------------------------------------------------------------------- View this GCN Circular online at https://gcn.nasa.gov/circulars/40476. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38507] GRB 250516A: AstroSat CZTI detection
by GCN Circulars 17 May '25

17 May '25

TITLE: GCN CIRCULAR NUMBER: 40475 SUBJECT: GRB 250516A: AstroSat CZTI detection DATE: 25/05/17 04:54:01 GMT FROM: Gaurav Waratkar at IIT Bombay <gauravwaratkar(a)iitb.ac.in> M. Tembhurnikar (IUCAA), G. Waratkar (IITB), A. Vibhute (IUCAA), V. Bhalerao (IITB), D. Bhattacharya (Ashoka University/IUCAA), A. R. Rao (IUCAA/TIFR), and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration: Analysis of AstroSat CZTI data with the CIFT framework (Sharma et al., 2021, JApA, 42, 73) showed the detection of a long duration GRB 250516A which was also detected by Fermi/GBM (Fermi GBM Team, GCN Circ. 40466), and Swift/BAT (Beardmore et al., GCN Circ. 40467). The source was clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve showed a single burst of emission that peaked at 2025-05-16 14:35:33.81 UTC. The measured peak count rate associated with the burst is 333 (+66, -72) counts/s above the background in the combined data of all quadrants, with a total of 527 (+187, -195) counts. The local mean background count rate was 1349 (+8, -9) counts/s. We measure a T90 of 2.4 (+1.8, -1.2) s from the cumulative Veto light curve. We note that our T90 is low since we detect just the brightest burst episode from the lightcurve seen in other missions (Fermi/GBM, Swift/BAT). This is likely due to the unfavourable orientation of our detectors with respect to the GRB. 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/40475. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38506] GRB 2500515A/GOTO25cqo: SVOM/VT optical blue color
by GCN Circulars 17 May '25

17 May '25

TITLE: GCN CIRCULAR NUMBER: 40474 SUBJECT: GRB 2500515A/GOTO25cqo: SVOM/VT optical blue color DATE: 25/05/17 01:24:43 GMT FROM: Huali Li at at NAOC, SVOM <lhl(a)nao.cas.cn> L. P. Xin, Y. L. Qiu, H. L. Li, C. Wu, Z. H. Yao, Y. N. Ma, 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), Y. Wang (PMO, CAS), R. Z. Li (YNAO, CAS), J. X. Cao, D. F. Kong (GXU), J. R. Mao (YNAO, CAS), X. W. Liu (YNU) report on behalf of the SVOM/VT team: SVOM/VT conducted ToO follow-up observations of the optical transient (B. P. Gompertz et al., GCN 40464) which was proposed to be the optical candidate of the GRB 250515A (Fermi GBM team, GCN 40462). The observation started from 2025-05-16T12:16:52 UTC (15.50 hours after the Fermi GBM trigger) to 2025-05-16T19:20:30 UTC in VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. The optical candidate (B. P. Gompertz et al., GCN 40464) was clearly detected in VT both channels, which is not found in the legacy survey. The brightness in AB magnitude was estimated to be: Mid time (hour) | Band | Exposure Time (second) | Magnitude | Magnitude error 22.27 | VT_B | 32x70 | 20.25 | 0.03 22.27 | VT_R | 32x70 | 20.56 | 0.05 Our photometry was not corrected for Galactic extinction. The source shows no significant fading or brightening in both channels during our observations. However, given the blue color and the possible association to the likely short GRB (Fermi GBM team, GCN 40462), more multiband follow-up observations are encouraged. 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/40474. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38505] GRB 250516A: Fermi GBM Observation
by GCN Circulars 16 May '25

16 May '25

TITLE: GCN CIRCULAR NUMBER: 40473 SUBJECT: GRB 250516A: Fermi GBM Observation DATE: 25/05/16 23:59:42 GMT FROM: oindabimukherjee(a)gmail.com O. Mukherjee (USRA) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 14:35:29.28 UT on 16 May 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250516A (trigger 769098934/250516608). which was also detected by Swift BAT (A. P. Beardmore et al. 2025, GCN 40467). The Fermi GBM on-ground location is consistent with the Swift BAT position. The angle from the Fermi LAT boresight is 36 degrees. The GBM light curve consists of two peaks with a duration (T90) of about 21.8 s (50-300 keV). The time-averaged spectrum from T0-1.4 to T0+25.2 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -1.26 +/- 0.07 and the cutoff energy, parameterized as Epeak, is 200 +/- 30 keV. The event fluence (10-1000 keV) in this time interval is (4.8 +/- 0.3)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0+5.1 s in the 10-1000 keV band is 5.8 +/- 0.3 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog: https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html For Fermi GBM data and info, please visit the official Fermi GBM Support Page: https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/" View this GCN Circular online at https://gcn.nasa.gov/circulars/40473. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38504] GRB 250516A: Swift-XRT refined Analysis
by GCN Circulars 16 May '25

16 May '25

TITLE: GCN CIRCULAR NUMBER: 40472 SUBJECT: GRB 250516A: Swift-XRT refined Analysis DATE: 25/05/16 23:13:02 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> A.P. Beardmore (U. Leicester), E. Ambrosi (INAF-IASFPA) , M. Capalbi (INAF-IASFPA), M. Perri (SSDC & INAF-OAR), J.A. Kennea (PSU), D.N. Burrows (PSU), M.A. Williams (PSU), J.P. Osborne (U. Leicester) and P.A. Evans report on behalf of the Swift-XRT team: We have analysed 6.8 ks of XRT data for GRB 250516A, from 108 s to 23.8 ks after the trigger. The data comprise 151 s in Windowed Timing (WT) mode with the remainder in Photon Counting (PC) mode. The late-time light curve (from T0+5.9 ks) can be modelled with a power-law decay with a decay index of alpha=1.45 (+0.18, -0.17). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 2.44 (+0.13, -0.12). The best-fitting absorption column is 3.5 (+0.5, -0.4) x 10^21 cm^-2, in excess of the Galactic value of 5.8 x 10^20 cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 1.98 (+/-0.12) and a best-fitting absorption column of 3.0 (+/-0.5) x 10^21 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.8 x 10^-11 (5.6 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 3.0 (+/-0.5) x 10^21 cm^-2 Galactic foreground: 5.8 x 10^20 cm^-2 Excess significance: 8.2 sigma Photon index: 1.98 (+/-0.12) If the light curve continues to decay with a power-law decay index of 1.45, the count rate at T+24 hours will be 5.8 x 10^-3 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.2 x 10^-13 (3.3 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/01314210. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/40472. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38503] GRB 250516A: Swift/UVOT Detection
by GCN Circulars 16 May '25

16 May '25

TITLE: GCN CIRCULAR NUMBER: 40471 SUBJECT: GRB 250516A: Swift/UVOT Detection DATE: 25/05/16 22:17:55 GMT FROM: Sam Shilling at Lancaster University <shilling.sam(a)gmail.com> S. P. R. Shilling (Lancaster U.) and A. P. Beardmore (U. Leicester) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 250516A 108 s after the BAT trigger (Beardmore et al., GCN Circ. 40467). A source consistent with the enhanced XRT position (Evans et al., GCN Circ. 40468) is detected in the initial UVOT exposures. The preliminary detection and 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag white 108 1715 411 20.5 +/- 0.3 v 650 1765 136 >18.5 b 576 1691 117 >19.2 u 320 1838 362 >19.7 w1 699 1814 117 >18.8 w2 626 1741 97 >19.1 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.062 in the direction of the burst (Schlegel et al. 1998). View this GCN Circular online at https://gcn.nasa.gov/circulars/40471. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38502] GRB 250515A: Swift ToO observations
by GCN Circulars 16 May '25

16 May '25

TITLE: GCN CIRCULAR NUMBER: 40470 SUBJECT: GRB 250515A: Swift ToO observations DATE: 25/05/16 21:26:55 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 250515A. Automated analysis of the XRT data will be presented online at https://www.swift.ac.uk/ToO_GRBs/00021829 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/40470. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38501] GRB 250516B: GECAM-B detection of a bright long burst
by GCN Circulars 16 May '25

16 May '25

TITLE: GCN CIRCULAR NUMBER: 40469 SUBJECT: GRB 250516B: GECAM-B detection of a bright long burst DATE: 25/05/16 19:33:50 GMT FROM: Chenwei Wang at IHEP <cwwang(a)ihep.ac.cn> Chen-Wei Wang, Shao-Lin Xiong (IHEP) report on behalf of GECAM team: GECAM-B was triggered in-flight by a bright long burst GRB 250516B at 2025-05-16T06:31:34.7 UTC (denoted as T0). According to the GECAM-B light curves in about 40-6000 keV, this burst mainly consists of multiple pulses with a duration (T90) of 40.6 +0.9/-0.7 s. The GECAM-B light curve can be found here: https://www.bursthub.cn//admin/static/gecamgrb250516B.png GECAM-B localized this burst to the following position (J2000): Ra: 137.5 deg Dec: 41.4 deg Err: 7.0 deg (1-sigma, statistical only) The time-averaged spectrum from T0-5 s to T0+75 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.00 +/-0.07 and the cutoff energy, parameterized as Epeak, is 367 +46/-36 keV. The event fluence (10-1000 keV) in this time interval is (2.3 +/-0.1)E-04 erg/cm^2. Thus GRB 250516B is consistent with Type II GRBs in the 'Amati' relation diagram, as shown at: https://www.bursthub.cn//admin/static/grb250516B_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/40469. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38500] GRB 250516A: Enhanced Swift-XRT position
by GCN Circulars 16 May '25

16 May '25

TITLE: GCN CIRCULAR NUMBER: 40468 SUBJECT: GRB 250516A: Enhanced Swift-XRT position DATE: 25/05/16 17:05:53 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> P.A. Evans, M.R. Goad, J.P. Osborne and A.P. Beardmore (U. Leicester) report on behalf of the Swift-XRT team. Using 1717 s of XRT Photon Counting mode data and 2 UVOT images for GRB 250516A, we find an astrometrically corrected X-ray position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 334.60978, -9.11949 which is equivalent to: RA (J2000): 22h 18m 26.35s Dec (J2000): -09d 07' 10.2" with an uncertainty of 2.2 arcsec (radius, 90% confidence). This position may be improved as more data are received. The latest position can be viewed at http://www.swift.ac.uk/xrt_positions. Position enhancement is described by Goad et al. (2007, A&A, 476, 1401) and Evans et al. (2009, MNRAS, 397, 1177). This circular was automatically generated, and is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/40468. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38499] GRB 250516A: Swift detection of a burst
by GCN Circulars 16 May '25

16 May '25

TITLE: GCN CIRCULAR NUMBER: 40467 SUBJECT: GRB 250516A: Swift detection of a burst DATE: 25/05/16 14:57:08 GMT FROM: K.L. Page at U Leicester <klp5(a)leicester.ac.uk> A. P. Beardmore (U Leicester), P. A. Evans (U Leicester), R. Gupta (NASA GSFC), K. L. Page (U Leicester), S. P. R. Shilling (Lancaster U.) and M. A. Williams (PSU) report on behalf of the Neil Gehrels Swift Observatory Team: At 14:35:29 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 250516A (trigger=1314210). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 334.561, -9.130 which is RA(J2000) = 22h 18m 15s Dec(J2000) = -09d 07' 48" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a complex structure with a duration of about 30 sec. The peak count rate was ~5000 counts/sec (15-350 keV), at ~5 sec after the trigger. The XRT began observing the field at 14:37:13.2 UT, 104.3 seconds after the BAT trigger. Using promptly downlinked data we find a fading, uncatalogued X-ray source with an enhanced position: RA, Dec 334.60979, -9.11941 which is equivalent to: RA(J2000) = 22h 18m 26.35s Dec(J2000) = -09d 07' 09.9" with an uncertainty of 1.9 arcseconds (radius, 90% containment). This location is 177 arcseconds from the BAT onboard position, within the BAT error circle. This position may be improved as more data are received; the latest position is available at https://www.swift.ac.uk/sper. A power-law fit to a spectrum formed from promptly downlinked event data gives a column density in excess of the Galactic value (5.84 x 10^20 cm^-2, Willingale et al. 2013), with an excess column of 1.8 (+1.47/-1.34) x 10^21 cm^-2 (90% confidence). UVOT took a finding chart exposure of 150 seconds with the White filter starting 108 seconds after the BAT trigger. No credible afterglow candidate has been found in the initial data products. The 2.7'x2.7' sub-image covers none of the XRT error circle. The 8'x8' region for the list of sources generated on-board covers 100% of the XRT error circle. The list of sources is typically complete to about 18 mag. No correction has been made for the expected extinction corresponding to E(B-V) of 0.062. Burst Advocate for this burst is A. P. Beardmore (apb AT star.le.ac.uk). 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/40467. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38498] GRB 250516A: Fermi GBM Final Real-time Localization
by GCN Circulars 16 May '25

16 May '25

TITLE: GCN CIRCULAR NUMBER: 40466 SUBJECT: GRB 250516A: Fermi GBM Final Real-time Localization DATE: 25/05/16 14:46:00 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 14:35:29 UT on 16 May 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250516A (trigger 769098934.27533 / 250516608). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 333.2, Dec = 0.1 (J2000 degrees, equivalent to J2000 22h 12m, 0d 06'), with a statistical uncertainty of 8.5 degrees. The angle from the Fermi LAT boresight is 27.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250516608/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250516608/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250516608/… View this GCN Circular online at https://gcn.nasa.gov/circulars/40466. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38497] GRB 250512B / EP250512a: SVOM/GRM analysis
by GCN Circulars 16 May '25

16 May '25

TITLE: GCN CIRCULAR NUMBER: 40465 SUBJECT: GRB 250512B / EP250512a: SVOM/GRM analysis DATE: 25/05/16 13:34:45 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: Nicolas Dagoneau, Stéphane Schanne (CEA) Report on behalf of the SVOM team: SVOM/GRM was triggered in-flight by the burst GRB 250512B (SVOM trigger reference: sb sb25051203) at 2025-05-12T11:20:08 UTC (T0), which is also detected by SVOM/ECLAIRs (Pierre Maggi et al., GCN #40439) , Einstein Probe (Zhao et al. GCN 40437) and Konus-Wind (D. Svinkin et al., GCN #40460). With the event-by-event data downloaded through the X-band ground station, we conducted the standard analysis pipeline of GRB 250512B. The GRM light curve shows that this burst consists of multi-episodes with a T90 of 179 +19/-7 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb250512B.png With the localization of ECLAIRs (RA=215.22, DEC=-10.1086), the time-averaged spectrum from T0-3 to T0+50 s (the main episode before the slew) is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -0.23 +0.42/-0.44 and the cutoff energy, parameterized as Epeak, is 70 +9/-6 keV. The event fluence (10-1000 keV) in this time interval is (3.1 +0.3/-0.2)E-06 erg/cm^2. 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. View this GCN Circular online at https://gcn.nasa.gov/circulars/40465. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38496] GRB 250515A: GOTO candidate optical counterpart
by GCN Circulars 16 May '25

16 May '25

TITLE: GCN CIRCULAR NUMBER: 40464 SUBJECT: GRB 250515A: GOTO candidate optical counterpart DATE: 25/05/16 09:20:14 GMT FROM: Ben Gompertz at U of Birmingham <b.gompertz(a)bham.ac.uk> B. P. Gompertz, R. Starling, D. O’Neill, G. Ramsay, A. Kumar, K. Ackley, M. Dyer, J. Lyman, K. Ulaczyk, D. Steeghs, D. Galloway, V. Dhillon, P. O'Brien, K. Noysena, R. Kotak, R. Breton, J. Casares, L. Nuttall, B. Godson, T. Killestein, and 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 short GRB 250515A (Fermi GBM team, GCN 40462). Targeted observations were performed by GOTO-North (La Palma) beginning at May 15 2025 21:21:20 UT, (+0.58h post trigger) and continuing through to May 16 2025 00:15:21 UT (+3.48h post trigger). 232 images were taken, across 10 unique pointings, covering 471.6 square degrees within the 90% localisation contour. ~60.1% of the total 2D localisation probability was covered, with an average 5-sigma depth of 19.8 mag in the GOTO L-band (400-700nm). 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, GOTO25cqo, is identified within the GBM 90% localisation region at RA 10:38:32.5, Dec +19:25:03.1 (J2000). This position is on the 37% probability contour of the Fermi/GBM localisation map. The source was initially detected with magnitude L = 20.17 ± 0.21 mag (+0.71h after the GBM trigger), rising to L = 19.79 ± 0.15 mag at +1.85h post trigger. In a 3rd epoch, taken at t0+2.99 hours, we obtain a 3-sigma upper limit of L > 19.21. We find no strong evidence of this source prior to the GRB trigger time in previous GOTO observations, the ZTF observations provided by the Lasair broker (Smith et al. 2019), or the ATLAS forced photometry server (Shingles et al. 2021). However, we caution that observations to sufficiently constraining depths are not available in the weeks prior to the GRB. We note a marginal flux excess in two ATLAS images taken on 2025-05-01 and 2025-05-03. Visual inspection of these images does not reveal any compelling source, and no significant flux excess was seen in the 7 epochs between these dates and GRB 250515A. From available observations, we cannot confirm whether GOTO25cqo is associated with GRB 250515A, but given its time coincidence and apparent rapid evolution, we encourage further follow-up observations. Magnitudes were calibrated using ATLAS-REFCAT2 (Tonry et al. 2018) and are not corrected for Galactic extinction. Observations are ongoing. 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/40464. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38495] MAXI GRB250515.65: Global MASTER-Net observations report
by GCN Circulars 16 May '25

16 May '25

TITLE: GCN CIRCULAR NUMBER: 40463 SUBJECT: MAXI GRB250515.65: Global MASTER-Net observations report DATE: 25/05/16 02:52:05 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 MAXI GRB250515.65 (trigger No 10849998,21h 14m 24.00s , -80d 30m 00.0s, R=1) errorbox 10 sec after notice time and 40345 sec after trigger time at 2025-05-16 02:41:33 UT, with upper limit up to 19.0 mag. The observations began at zenith distance = 50 deg. The sun altitude is -33.6 deg. MASTER-OAFA robotic telescope located in Argentina (OAFA observatory of San Juan National University) started inspect of the MAXI GRB250515.65 errorbox 79 sec after notice time and 40414 sec after trigger time at 2025-05-16 02:42:42 UT, with upper limit up to 18.6 mag. The observations began at zenith distance = 61 deg. The sun altitude is -62.8 deg. The galactic latitude b = -33 deg., longitude l = 312 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2871800 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 40376 | 2025-05-16 02:41:33 | MASTER-SAAO | (21h 16m 32.15s , -80d 50m 43.5s) | C | 60 | 18.1 | 40436 | 2025-05-16 02:41:33 | MASTER-SAAO | (21h 16m 32.15s , -80d 50m 43.5s) | C | 180 | 19.0 | Coadd 40495 | 2025-05-16 02:42:42 | MASTER-OAFA | (20h 13m 48.68s , -81d 25m 05.7s) | C | 160 | 17.6 | 40505 | 2025-05-16 02:42:43 | MASTER-OAFA | (21h 11m 07.77s , -80d 47m 38.7s) | C | 180 | 18.6 | 40454 | 2025-05-16 02:42:52 | MASTER-SAAO | (21h 16m 31.94s , -80d 50m 47.8s) | C | 60 | 18.3 | 40534 | 2025-05-16 02:44:11 | MASTER-SAAO | (21h 16m 31.62s , -80d 50m 49.7s) | C | 60 | 18.2 | 40613 | 2025-05-16 02:45:30 | MASTER-SAAO | (21h 16m 31.26s , -80d 50m 50.6s) | C | 60 | 18.2 | 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/40463. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38494] GRB 250515A: Fermi GBM Final Localization
by GCN Circulars 15 May '25

15 May '25

TITLE: GCN CIRCULAR NUMBER: 40462 SUBJECT: GRB 250515A: Fermi GBM Final Localization DATE: 25/05/15 21:34:47 GMT FROM: R. Hamburg at CNRS/IJCLab <rachel.k.hamburg(a)gmail.com> The Fermi GBM team reports the detection of a likely SHORT GRB "At 20:46:21.91 UT on 15 May 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250515A (trigger 769034786/250515866). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 154.35, Dec = 23.19 (J2000 degrees, equivalent to J2000 10h 17m, +23d 11'), with a statistical uncertainty of 7.76 degrees. The angle from the Fermi LAT boresight is 69 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250515866/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250515866/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250515866/…" View this GCN Circular online at https://gcn.nasa.gov/circulars/40462. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38493] GRB 250424A: COLIBRÍ detection of the associated supernova
by GCN Circulars 15 May '25

15 May '25

TITLE: GCN CIRCULAR NUMBER: 40461 SUBJECT: GRB 250424A: COLIBRÍ detection of the associated supernova DATE: 25/05/15 16:39:06 GMT FROM: Antonio de Ugarte Postigo at LAM, CNRS <adeugartepostigo(a)gmail.com> Antonio de Ugarte Postigo (LAM), Benjamin Schneider (LAM), Stéphane Basa (UAR Pytheas), Ny Avo Rakotondrainibe (LAM), Alan M. Watson (UNAM), Kin Ocelotl López (UNAM), William H. Lee (UNAM), Fredd Alvarez (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (AUS), Sarah Antier (OCA), Rosa L. Becerra (U Roma), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Noémie Globus (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), and Margarita Pereyra (UNAM): We have continued imaging the field of GRB 250424A (Cenko et al., GCN Circ. 40224 <https://gcn.nasa.gov/circulars/40224>; Harsha et al. GCN Circ. 40231; Ridnaia et al. GCN Circ. 40243; McKenna et al. GCN Circ. 40249; Zhang et al. GCN Circ. 40252; Nakahira et al. GCN Circ. 40298) at a redshift of z = 0.310 (Saccardi et al. GCN Circ. 40228) to monitor the evolution of the optical transient (Brivio et al. GCN Circ. 40225; Becerra et al. GCN Circ. 40226; de Wet et al. GCN Circ. 40229; Ducoin et al. GCN Circ. 40230; Turpin et al. GCN Circ. 40240; Dutton et al. GCN Circ. 40241; Siegel et al. GCN Circ. 40244; Hu et al. GCN Circ. 40246; Schneider et al. GCN Circ. 40250; Elkabir et al. GCN Circ. 40251; Ghosh et al. GCN Circ. 40263), in search for the possible SN emission, using the DDRAGO wide-field imager on the COLIBRÍ telescope. The field is covered by the Legacy Survey, which reveals an underlying host galaxy with AB magnitudes g=22.60, r=21.98, i=22.05 (Pérez-Fournon et al. GCN Circ. 40227). A GRB-SN at that redshift would be expected to reach peak light between the 8th and the 15th of May (Cano et al. 2017). We hereby report two photometric observations of the optical counterpart obtained in the r- and i-bands. 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. An r-band observation consisting of 112x60s exposures was obtained with mean epoch 2025-05-11 06:49:32 UTC (16.998 d after the burst, 12.976 d in the rest frame). We measure r = 21.54 +/- 0.21 mag. An i-band observation consisting of 111x60s exposures was obtained with mean epoch 2025-05-15 06:42:39 UTC (20.993 d after the burst, 16.025 in the rest frame). We measure i = 21.46 +/- 0.12 mag. Both values are clearly in excess of the underlying host galaxy, and indeed an excess emission is obtained when performing image subtraction with respect to the archival Legacy Survey image. Subtracting the host contribution we obtain values of r ~ 22.7 mag and i ~ 22.4 mag which are in agreement to the expectations of a GRB-SN at this redshift with a certain amount of extinction. We consequently suggest that COLIBRÍ is currently detecting the supernova associated with GRB 250424A. Further observations to confirm and monitor the evolution of this GRB-SN are encouraged. 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/40461. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38492] GRB 250424A: COLIBRÍ detection of the associated supernova
by GCN Circulars 15 May '25

15 May '25

TITLE: GCN CIRCULAR NUMBER: 40461 SUBJECT: GRB 250424A: COLIBRÍ detection of the associated supernova DATE: 25/05/15 16:39:06 GMT FROM: Antonio de Ugarte Postigo at LAM, CNRS <adeugartepostigo(a)gmail.com> Antonio de Ugarte Postigo (LAM), Benjamin Schneider (LAM), Stéphane Basa (UAR Pytheas), Ny Avo Rakotondrainibe (LAM), Alan M. Watson (UNAM), Kin Ocelotl López (UNAM), William H. Lee (UNAM), Fredd Alvarez (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (AUS), Sarah Antier (OCA), Rosa L. Becerra (U Roma), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Noémie Globus (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), and Margarita Pereyra (UNAM): We have continued imaging the field of GRB 250424A (Cenko et al., GCN Circ. 40224 <https://gcn.nasa.gov/circulars/40224>; Harsha et al. GCN Circ. 40231; Ridnaia et al. GCN Circ. 40243; McKenna et al. GCN Circ. 40249; Zhang et al. GCN Circ. 40252; Nakahira et al. GCN Circ. 40298) at a redshift of z = 0.310 (Saccardi et al. GCN Circ. 40228) to monitor the evolution of the optical transient (Brivio et al. GCN Circ. 40225; Becerra et al. GCN Circ. 40226; de Wet et al. GCN Circ. 40229; Ducoin et al. GCN Circ. 40230; Turpin et al. GCN Circ. 40240; Dutton et al. GCN Circ. 40241; Siegel et al. GCN Circ. 40244; Hu et al. GCN Circ. 40246; Schneider et al. GCN Circ. 40250; Elkabir et al. GCN Circ. 40251; Ghosh et al. GCN Circ. 40263), in search for the possible SN emission, using the DDRAGO wide-field imager on the COLIBRÍ telescope. The field is covered by the Legacy Survey, which reveals an underlying host galaxy with AB magnitudes g=22.60, r=21.98, i=22.05 (Pérez-Fournon et al. GCN Circ. 40227). A GRB-SN at that redshift would be expected to reach peak light between the 8th and the 15th of May (Cano et al. 2017). We hereby report two photometric observations of the optical counterpart obtained in the r- and i-bands. 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. An r-band observation consisting of 112x60s exposures was obtained with mean epoch 2025-05-11 06:49:32 UTC (16.998 d after the burst, 12.976 d in the rest frame). We measure r = 21.54 +/- 0.21 mag. An i-band observation consisting of 111x60s exposures was obtained with mean epoch 2025-05-15 06:42:39 UTC (20.993 d after the burst, 16.025 in the rest frame). We measure i = 21.46 +/- 0.12 mag. Both values are clearly in excess of the underlying host galaxy, and indeed an excess emission is obtained when performing image subtraction with respect to the archival Legacy Survey image. Subtracting the host contribution we obtain values of r ~ 22.7 mag and i ~ 22.4 mag which are in agreement to the expectations of a GRB-SN at this redshift with a certain amount of extinction. We consequently suggest that COLIBRÍ is currently detecting the supernova associated with GRB 250424A. Further observations to confirm and monitor the evolution of this GRB-SN are encouraged. 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/40461. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38491] Konus-Wind detection of GRB 250512B / EP250512a
by GCN Circulars 15 May '25

15 May '25

TITLE: GCN CIRCULAR NUMBER: 40460 SUBJECT: Konus-Wind detection of GRB 250512B / EP250512a DATE: 25/05/15 11:03:14 GMT FROM: Dmitry Svinkin at Ioffe Institute <svinkin(a)mail.ioffe.ru> D. Svinkin, D. Frederiks, A.Lysenko, A. Ridnaia, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report: The long-duration GRB 250512B / EP250512a (EP-WXT detection: Zhao et al., GCN 40437; Yang et al., GCN 40448; SVOM-ECLAIRs detection: Maggi et al., GCN 40439) was detected by Konus-Wind (KW) in the waiting mode at about T0 = T0(EP) = 40803 s UT (11:20:03). A Bayesian block analysis of the KW waiting mode data in the 20-400 keV band reveals a ~8 sigma count-rate increase in the interval from T0+7.4 s to T0+113.3 s. The KW light curve of this burst is available at http://www.ioffe.ru/LEA/GRBs/GRB250512B/ The total burst fluence is 6.68(-2.23,+1.59)x10^-6 erg/cm^2, and the 2.944 s peak energy flux, measured from T0+10.309 s, is 3.08(-1.14,+0.89)x10^-7 erg/cm^2. (both in the 20 keV - 10 MeV energy range). The time-integrated spectrum of the burst, measured from T0+7.4 s to T0+113.3 s, can be described by a power law with exponential cutoff (CPL) model dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) with alpha > -1.82 and Ep = 114(-37,+57) keV. All the quoted errors are estimated at the 68% confidence level. All the presented results are preliminary. View this GCN Circular online at https://gcn.nasa.gov/circulars/40460. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38490] GRB 250502A: TESS observations
by GCN Circulars 14 May '25

14 May '25

TITLE: GCN CIRCULAR NUMBER: 40459 SUBJECT: GRB 250502A: TESS observations DATE: 25/05/14 20:02:36 GMT FROM: Rahul Jayaraman at MIT <rjayaram(a)mit.edu> R. Jayaraman (MIT), M.M. Fausnaugh (TTU), S. Chastain (TTU), R. Vanderspek (MIT), and G.R. Ricker (MIT) report: The Transiting Exoplanet Survey Satellite (TESS; Ricker et al., JATIS 1 2015) observed GRB 250502A (Wang et al., GCN 40313) during Sector 91 of its scheduled sky survey. We performed forced difference-imaging photometry at the location of the confirmed X-ray afterglow (Dichiara et al., GCN 40336) using the full-frame images from the publicly-available TICA data archived at MAST (https://archive.stsci.edu/hlsp/tica). Our data reduction routine is described in Fausnaugh et al. 2023 (ApJ 956(2):108). The light curve shows a rapidly rising afterglow in the three 200s exposures from after the trigger. The light curve peaks roughly ~700 s after the burst at a magnitude of 16.44 ± 0.14 (uncorrected for Galactic extinction), followed by a decay to the detection limit of 17.6 (3-sigma) over ~4 x 10^3 s. These results are consistent with measurements of the early afterglow from Rakotondrainibe et al. (GCN 40315), Xu et al. (GCN 40319), and Li et al. (GCN 40320). This circular includes data collected with the TESS mission, obtained from the MAST data archive at the Space Telescope Science Institute (STScI). Funding for the TESS mission is provided by the NASA Explorer Program. STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. View this GCN Circular online at https://gcn.nasa.gov/circulars/40459. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38489] Fermi trigger No 768922089: Global MASTER-Net observations report
by GCN Circulars 14 May '25

14 May '25

TITLE: GCN CIRCULAR NUMBER: 40458 SUBJECT: Fermi trigger No 768922089: Global MASTER-Net observations report DATE: 25/05/14 19:46:06 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 GRB250514.56 (trigger No 768922089,16h 41m 45.60s , +29d 45m 00.0s, R=11.68) errorbox 21929 sec after notice time and 21974 sec after trigger time at 2025-05-14 19:34:19 UT, with upper limit up to 16.9 mag. The observations began at zenith distance = 79 deg. The sun altitude is -47.5 deg. The galactic latitude b = 39 deg., longitude l = 50 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2870382 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 22004 | 2025-05-14 19:34:19 | MASTER-SAAO | (15h 59m 51.82s , +28d 44m 08.0s) | C | 60 | 16.9 | 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/40458. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38488] GRB 250511A: GECAM-A detection of a short burst
by GCN Circulars 14 May '25

14 May '25

TITLE: GCN CIRCULAR NUMBER: 40457 SUBJECT: GRB 250511A: GECAM-A detection of a short burst DATE: 25/05/14 04:36:21 GMT FROM: Chenwei Wang at IHEP <cwwang(a)ihep.ac.cn> Chen-Wei Wang, Shao-Lin Xiong, Yue Huang (IHEP) report on behalf of GECAM team: GECAM-A detected a short burst GRB 250511A at 2025-05-11T00:52:17 UTC (denoted as T0). According to the GECAM-A light curves in about 40-6000 keV, this burst mainly consists of a single pulse with a duration (T90) of 1.9 +0.7/-0.7 s. The GECAM-A light curve can be found here: https://www.bursthub.cn//admin/static/gecamgrb250511A.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/40457. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38487] GRB 250509A: Swift-BAT refined analysis
by GCN Circulars 14 May '25

14 May '25

TITLE: GCN CIRCULAR NUMBER: 40456 SUBJECT: GRB 250509A: Swift-BAT refined analysis DATE: 25/05/14 02:57:21 GMT FROM: Rahul Gupta at NASA GSFC <rahul.gupta(a)nasa.gov> T. Parsotan (GSFC), S. D. Barthelmy (GSFC), R. Gupta (GSFC), H. A. Krimm (NSF), S. Laha (GSFC/UMBC), A. Y. Lien (U Tampa), C. B. Markwardt (GSFC), M. J. Moss (GSFC), D. M. Palmer (LANL), D. Sadaula (GSFC/UMBC), T. Sakamoto (AGU), M. H. Siegel (PSU) (i.e. the Swift-BAT team): Using the data set from T-239 to T+963 sec from the recent telemetry downlink, we report further analysis of BAT GRB 250509A (trigger #1311764) (Siegel, et al., GCN Circ. 40407). The BAT ground-calculated position is RA, Dec = 46.451, -38.854 deg which is RA(J2000) = 03h 05m 48.3s Dec(J2000) = -38d 51' 15.1" with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment). The partial coding was 96%. The mask-weighted BAT light curve shows a sharp rise and exponential decay profile. T90 (15-350 keV) is 55.43 +- 10.47 sec (estimated error including systematics). The time-averaged spectrum from T-2.85 to T+71.46 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.54 +- 0.08. The fluence in the 15-150 keV band is 2.4 +- 0.1 x 10^-06 erg/cm2. The 1-sec peak photon flux measured from T+0.42 sec in the 15-150 keV band is 1.9 +- 0.2 ph/cm2/sec. All the quoted errors are at the 90% confidence level. The results of the batgrbproduct analysis are available at https://swift.gsfc.nasa.gov/results/batgrbcat/BAT_refined_circular/1311764 View this GCN Circular online at https://gcn.nasa.gov/circulars/40456. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38486] LIGO/Virgo/KAGRA S250328ae: DECam DESGW Candidates (Final Epochs)
by GCN Circulars 13 May '25

13 May '25

TITLE: GCN CIRCULAR NUMBER: 40455 SUBJECT: LIGO/Virgo/KAGRA S250328ae: DECam DESGW Candidates (Final Epochs) DATE: 25/05/13 17:45:36 GMT FROM: Isaac McMahon at University of Zürich <isaac.mcmahon(a)ligo.org> Isaac McMahon, Sean MacBride, Marcelle Soares-Santos (UZH), Simran Kaur (U. of Michigan/UZH), Lillian Joseph (Benedictine U.), Ken Herner, Tom Diehl (Fermilab), Haibin Zhang, Mitsuru Kokubo, Nozomu Tominaga, Yousuke Utsumi, Michitoshi Yoshida (NAOJ), Tomoki Morokuma (Chiba Tech), Akira Arai, Wanqui He, Yuki Moritani, Masato Onodera, Vera Maria Passegger, Ichi Tanaka, Kiyoto Yabe (NAOJ) report on behalf of the Dark Energy Survey Gravitational Wave (DESGW) Team, the Japanese Collaboration for Gravitational-Wave Electro-Magnetic Follow-up (J-GEM), and Subaru Telescope: At 01:20 UTC April 6th and 00:14 UTC April 25th, the Dark Energy Camera (DECam) began the third and fourth epochs of observations in final response to the LVK alert issued for the candidate gravitational-wave event S250328ae (GCN 39898). The pointings of these observations were identical to the first epoch observations from March 29th, 2025 (GCN 39934). All fields were observed in DECam r, i, and z filters with 90-second exposures. The limiting magnitude achieved is ~21.3 in r-band, ~21.2 in i-band, and ~21.0 in z-band for the third epoch and ~22.3 in r-band, ~22.1 in i-band, and ~21.6 in z-band for the fourth. We process the images with our difference imaging pipeline (Herner et al. 2020) using DES and public DECam images as templates. We employ the autoscan machine learning code (Goldstein et al 2015) to reject subtraction artifacts, requiring an autoscan score of at least 0.7 on at least 3 nights of observations. We also match our candidates against the ALLWISE, Milliquas, Quaia, and LQAC-6 AGN catalogs (Secrest et al 2015, Flesch 2023, Storey-Fisher et al 2024, Souchay et al 2024) within the LVK localization volume. Of the 88 AGNs which exhibited transient variability in our observations, none lay within the localization volume. Of the 25 high confidence candidates reported previously (GCN 39992), 15 were observed by the J-GEM collaboration, using the Subaru Telescope Prime Focus Spectrograph (PFS), and ruled out by spectral identification and redshift (GCN 40221). Another 8 candidates either did not exhibit any further transient activity after the first two epochs or were determined to be likely stellar in origin. The final 2 candidates were not within the footprint observed by J-GEM and thus could not be determined. We report these two candidates and one last candidate which was observed only in the most recent epochs below, all likely of supernova origin. | TYPE | ID | ATNAME | RA | DEC | MAG_R | MAG_R_ERR | MAG_I | MAG_I_ERR | MAG_Z | MAG_Z_ERR | | -------- | ------- | --------- | ---------- | ---------- | ----- | ---- | ----- | ---- | ----- | ---- | | SN_LIKE | 2290001 | AT2025avp | 144.806008 | 10.632223 | 20.36 | 0.02 | 20.19 | 0.02 | 20.22 | 0.06 | | SN_LIKE | 2291473 | AT2025gem | 144.706509 | 11.560317 | 20.92 | 0.03 | 21.03 | 0.15 | 21.22 | 0.10 | | SN_LIKE | 2295351 | AT2025kjv | 143.077064 | 7.385021 | 22.3 | 0.10 | 21.81 | 0.07 | 22.86 | 0.44 | Additionally, J-GEM reported 5 QSOs which had a redshift consistent with the localization volume. We do not find any evidence of any transient variability for any of these QSOs in our observations after the detection of S250328ae. We also do not recover any of the X-ray source candidates reported by Swift XRT (GCN 39972) within their reported error bounds. Thus, apart from the possibility that the three supernova-like candidates reported above are related to S250328ae, we find no suitable optical counterpart candidate for this binary black hole gravitational wave event. The DECam Search & Discovery Program for Optical Signatures of Gravitational Wave Events (DESGW) is carried out by the Dark Energy Survey (DES) collaboration in partnership with wide-ranging groups in the community. DESGW uses data obtained with the Dark Energy Camera (DECam), which was constructed by the DES collaboration with support from the Department of Energy and member institutions, and utilizes data as distributed by the Science Data Archive at NOIRLAB. NOIRLAB is operated by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation. We thank the Cerro Tololo observatory staff for their support in acquiring these observations. We also thank the J-GEM and Swift XRT teams for their contribution and support. We are grateful to the staff at NAOJ and Subaru Telescope for their contributions to the deployments of PFS hardware and software, and the preparations of PFS system integration, engineering observations, and various other engineering works. Our thanks should also be propagated to the administrative staffs at Kavli IPMU, NAOJ, Subaru Telescope, and all the PFS institutes for kind support in such aspects as finances, contracts, asset managements, and so on. This research is based on data collected at the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan. We are honored and grateful for the opportunity of observing the Universe from Maunakea, which has cultural, historical, and natural significance in Hawaii. View this GCN Circular online at https://gcn.nasa.gov/circulars/40455. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38485] Fermi GRB 250512A: Global MASTER-Net observations report
by GCN Circulars 13 May '25

13 May '25

TITLE: GCN CIRCULAR NUMBER: 40454 SUBJECT: Fermi GRB 250512A: Global MASTER-Net observations report DATE: 25/05/13 16:16:08 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 250512A ( Fermi GBM team, GCN 40436) errorbox 1 days 10178 sec after notice time and 1 days 10229 sec after trigger time at 2025-05-13 14:52:05 UT, with upper limit up to 17.9 mag. Observations started at twilight. The observations began at zenith distance = 38 deg. The sun altitude is -14.8 deg. The galactic latitude b = 19 deg., longitude l = 112 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2868622 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 96660 | 2025-05-13 14:52:05 | MASTER-Tunka | (17h 57m 54.62s , +86d 24m 49.3s) | C | 60 | 14.5 | 96798 | 2025-05-13 14:54:24 | MASTER-Tunka | (20h 39m 40.13s , +76d 43m 27.8s) | C | 60 | 13.0 | 96962 | 2025-05-13 14:57:08 | MASTER-Tunka | (21h 30m 19.84s , +78d 37m 25.1s) | C | 60 | 13.4 | 100410 | 2025-05-13 15:54:36 | MASTER-Tunka | (18h 00m 35.78s , +86d 29m 00.2s) | C | 60 | 17.8 | 100410 | 2025-05-13 15:54:36 | MASTER- | (17h 52m 00.08s , +86d 24m 46.8s) | C | 60 | 17.5 | 100489 | 2025-05-13 15:55:55 | MASTER-Tunka | (20h 40m 09.79s , +76d 45m 49.8s) | C | 60 | 17.9 | 100489 | 2025-05-13 15:55:55 | MASTER- | (20h 37m 45.37s , +76d 40m 53.1s) | C | 60 | 17.4 | 100690 | 2025-05-13 15:59:16 | MASTER-Tunka | (21h 31m 11.48s , +78d 36m 43.9s) | C | 60 | 17.7 | 100871 | 2025-05-13 16:02:17 | MASTER-Tunka | (21h 47m 34.81s , +76d 42m 05.1s) | C | 60 | 17.1 | 100871 | 2025-05-13 16:02:17 | MASTER- | (21h 45m 01.87s , +76d 37m 00.9s) | C | 60 | 16.4 | Coadd 101045 | 2025-05-13 16:05:11 | MASTER-Tunka | (18h 00m 13.68s , +86d 28m 34.8s) | C | 60 | 17.0 | 101129 | 2025-05-13 16:06:35 | MASTER-Tunka | (20h 40m 08.00s , +76d 47m 07.4s) | C | 60 | 16.6 | 101209 | 2025-05-13 16:07:54 | MASTER-Tunka | (21h 02m 16.63s , +74d 50m 57.9s) | C | 60 | 17.0 | 101287 | 2025-05-13 16:09:13 | MASTER-Tunka | (21h 31m 11.49s , +78d 36m 46.3s) | C | 60 | 17.4 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. View this GCN Circular online at https://gcn.nasa.gov/circulars/40454. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38484] Konus-Wind detection of GRB 250506A
by GCN Circulars 13 May '25

13 May '25

TITLE: GCN CIRCULAR NUMBER: 40453 SUBJECT: Konus-Wind detection of GRB 250506A DATE: 25/05/13 10:36:33 GMT FROM: Dmitry Svinkin at Ioffe Institute <svinkin(a)mail.ioffe.ru> D. Svinkin, D. Frederiks, A. Lysenko, A. Ridnaia, A. Tsvetkova, M. Ulanov, and T. Cline on behalf of the Konus-Wind team, report: The long-duration GRB 250506A (Fermi-GBM detection: The Fermi GBM team, GCN 40355; SVOM detection: Wang et al., GCN 40358; GECAM-B detection: Wang et al., GCN 40396; GRBAlpha detection: Pal et al., GCN 40440;) triggered Konus-Wind at T0=08605.817 s UT (02:23:25.817). The burst light curve shows a multi-peaked structure which starts at ~T0-2.1 s and has a total duration of ~56 s. The emission is seen up to ~7 MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB250506_T08605 As observed by Konus-Wind, the burst had a fluence of 2.41(-0.16,+0.38)x10^-5 erg/cm2, and a 64-ms peak flux, measured from T0+33.728 s, of 8.39(-0.74,+0.75)x10^-6 erg/cm2/s (both in the 20 keV - 10 MeV energy range). The time-averaged spectrum of the burst (measured from T0 to T0+57.600 s) is best fit in the 20 keV - 10 MeV range by the GRB (Band) model with the following parameters: the low-energy photon index alpha = -1.06(-0.04,+0.08), the high energy photon index beta = -3.51(-6.49,+0.91), the peak energy Ep = 284(-28,+28) keV (chi2 = 123/97 dof). The spectrum near the maximum count rate (measured from T0+33.024 to T0+41.216 s) is best fit in the 20 keV - 10 MeV range by a power law with exponential cutoff model: dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) with alpha = -1.02(-0.07,+0.08) and Ep = 278(-21,+25) keV (chi2 = 111/98 dof). Fitting by a GRB (Band) model yields the same alpha and Ep, and an upper limit on the high energy photon index: beta < -3.0 (chi2 = 111/97 dof). All the quoted errors are at the 68% confidence level. All the quoted values are preliminary. View this GCN Circular online at https://gcn.nasa.gov/circulars/40453. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38483] EP250512a/GRB 250512B: REM optical/NIR observations
by GCN Circulars 13 May '25

13 May '25

TITLE: GCN CIRCULAR NUMBER: 40452 SUBJECT: EP250512a/GRB 250512B: REM optical/NIR observations DATE: 25/05/13 10:28:43 GMT FROM: Riccardo Brivio at INAF-OAB <riccardo.brivio(a)inaf.it> R. Brivio, M. Ferro, P. D'Avanzo, S. Covino, D. Fugazza (INAF-OAB) report on behalf of the REM team: We observed the field of EP250512a/GRB 250512B detected by EP/WXT (Zhao et al., GCN 40437) and SVOM/ECLAIRs (Maggi et al., GCN 40439) with the REM 60 cm robotic telescope located at the ESO observatory of La Silla (Chile). The observations were carried in the g, r, i, z, J, H, and K bands, started on 2025 May 12 at 22:52:55 UT (i.e. 11.5 hr after the burst), and lasted for about 1 hour. From preliminary inspection, we do not detect any possible counterpart consistent with the afterglow (Li et al., GCN 40443; Xin et al., GCN 40444; Busmann et al., GCN 40447) down to the following 3sigma limits: r > 18.9 (AB; calibrated against the Pan-STARRS catalogue), at a mid-time of 12.0 hr after the trigger; H > 16.2 (Vega; calibrated against the 2MASS catalogue), at a mid-time of 11.9 hr after the trigger. View this GCN Circular online at https://gcn.nasa.gov/circulars/40452. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38482] EP250511a: Koshka Zeiss-1000 Optical Upper Limit
by GCN Circulars 13 May '25

13 May '25

TITLE: GCN CIRCULAR NUMBER: 40451 SUBJECT: EP250511a: Koshka Zeiss-1000 Optical Upper Limit DATE: 25/05/13 10:27:04 GMT FROM: Nicolai Pankov at HSE, IKI RAS <colinsergesen(a)gmail.com> N. Pankov (HSE, IKI), A. Novichonok (Petrozavodsk State University, KIAM), I. Nikolenko (INASAN), A. Pozanenko (IKI) report on behalf of IKI-GRB-FuN: We performed optical observations of the field of EP250511a (Lian et. al, GCN 40429; Li et. al, GCN 40434) using the 1-meter Zeiss-1000 telescope of the Simeiz (Koshka) Observatory. The R-band observations began on 2025-05-11 19:37:13 UT, i.e. ~0.51 days since trigger at a low altitude (~40 deg) and in the presence of the full Moon. The optical counterpart (Schneider et. al, GCN 40431; Li et. al, GCN 40433; Sanchez-Sierras et. al, GCN 40449) is not detected in the stacked image of an exposure of 86*60 sec. The preliminary upper limit is given below: Date UT start t-T0 Exp. Filter OT Err. UL (mid, days) (n*s) (3sigma) 2025-05-11 19:37:13 0.51405 86*60 R n/d n/d 18.9 The photometry was calibrated using nearby stars from USNO-B1.0 and has not been corrected for the Galactic extinction. Our result is consistent with non-detections reported by (Lipunov et. al, GCN 40432; Brivio et. al, GCN 40435; Zhong et. al, GCN 40442; Busmann et. al, GCN 40445). Ref. stars USNO-B1.0 RA Dec R2 202.1106 -2.6632 15.94 202.0790 -2.7119 15.27 202.0868 -2.7163 15.00 View this GCN Circular online at https://gcn.nasa.gov/circulars/40451. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38481] GRB 250507B: AstroSat CZTI detection
by GCN Circulars 13 May '25

13 May '25

TITLE: GCN CIRCULAR NUMBER: 40450 SUBJECT: GRB 250507B: AstroSat CZTI detection DATE: 25/05/13 09:42:32 GMT FROM: Gaurav Waratkar at IIT Bombay <gauravwaratkar(a)iitb.ac.in> M. Tembhurnikar (IUCAA), G. Waratkar (IITB), A. Vibhute (IUCAA), V. Bhalerao (IITB), D. Bhattacharya (Ashoka University/IUCAA), A. R. Rao (IUCAA/TIFR), and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration: Analysis of AstroSat CZTI data with the CIFT framework (Sharma et al., 2021, JApA, 42, 73) showed the detection of GRB 250507B which was also detected by SVOM/GRM (SVOM/GRM team, GCN Circ. 40438) and GRBAlpha (Pal et al., GCN Circ. 40441). The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2025-05-07 09:31:33.55 UTC. The measured peak count rate associated with the burst is 158 (+90, -40) counts/s above the background in the combined data of two quadrants (out of four), with a total of 70 (+31, -29) counts. The local mean background count rate was 128 (+5, -8) counts/s. Using cumulative rates, we measure a T90 of 0.7 (+0.2, -0.3) s. We detect only the brighter part of the pulse detected by SVOM/GRM, likely because the source is at a sky position where our effective area is low. The source was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve peaks at 2025-05-07 09:31:32.65 UTC. The measured peak count rate associated with the burst is 262 (+67, -44) counts/s above the background in the combined data of all quadrants, with a total of 613 (+161, -168) counts. The local mean background count rate was 1220 (+8, -8) counts/s. Due to the intrinsic 1 s binning of veto data, we cannot reliably estimate a T90 from it. 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/40450. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38480] EP250511a: Gemini optical counterpart observation
by GCN Circulars 13 May '25

13 May '25

TITLE: GCN CIRCULAR NUMBER: 40449 SUBJECT: EP250511a: Gemini optical counterpart observation DATE: 25/05/13 09:07:23 GMT FROM: Antonio Martin-Carrillo at UCD,Space Science Group <antonio.martin-carrillo(a)ucd.ie> J. Sanchez-Sierras (Radboud), R. A. J. Eyles-Ferris (Leicester), A. Martin-Carrillo (UCD), A. J. Levan (Radboud and Warwick), G. Corcoran (UCD), P. G. Jonker (Radboud), F. E. Bauer (SSI and UTA), D. B. Malesani (DAWN/NBI and Radboud), J. A. Quirola-Vasquez (Radboud), report on behalf of a larger collaboration: We observed the field of the fast X-ray transient EP250511a (Lian et al., GCN 40429) using the Gemini-South telescope. Observations started on 2025 May 12 at 01:19:15 UT (17.32 hr after the EP trigger), and consisted of 5x60 s exposures in each of the SDSS i and z bands. At the location of the optical counterpart reported by Schneider et al. (GCN 40431) and Li et al. (GCN 40433) an extended source is clearly visible, with a magnitude of i = 23.04 +/- 0.06 (AB system, calibrated against nearby Pan-STARRS objects). This magnitude is brighter than the archival value reported in the Legacy Survey for the underlying candidate host galaxy (Schneider et al., GCN 40431). Image subtraction using PyZOGY (Zackay et al. 2016, doi:10.3847/0004-637X/830/1/27), using the Legacy Survey as template, reveals indeed a residual source with magnitude, i = 23.64 +/- 0.26 (AB system). We thank excellent support from the observing staff at Gemini, in particular Cinthya Rodrigez and Joan Font. View this GCN Circular online at https://gcn.nasa.gov/circulars/40449. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38479] EP250512a/GRB 250512B refined analysis of the EP-WXT and EP-FXT observations
by GCN Circulars 13 May '25

13 May '25

TITLE: GCN CIRCULAR NUMBER: 40448 SUBJECT: EP250512a/GRB 250512B refined analysis of the EP-WXT and EP-FXT observations DATE: 25/05/13 07:02:52 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> H.N. Yang, D. H. Zhao (NAO, CAS), Y. L. Hua (PMO, CAS), Y. J. Zhang (THU), M. J. Liu, J. W. Hu, H. W. Pan, Y. Liu (NAO, CAS), on behalf of the Einstein Probe (EP) team: The X-ray transient EP250512a was detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (D. H. Zhao et al. GCN 40437). It was also detected by SVOM/ECLAIRs (Pierre Maggi et al. GCN 40439), and followed up by several telescopes ( H. L. Li et al. GCN 40443; L. P. Xin et al. GCN 40444; V.Lipunov et al. GCN 40446; Malte Busmann et al. GCN 40447). Refined analysis of the WXT data shows that the event started at T0 = 2025-05-12T11:20:03 (UTC) and lasted for about 360 s (T90). The peak flux is about 4.2 x 10^(-9) erg/s/cm^2 (T0+135 s). The averaged 0.5-4 keV spectrum of T90 can be fitted by an absorbed power law model with a Galactic hydrogen column density of 5.7 x 10^20 cm^-2 and a photon index of 1.31 (-0.17/+0.18). The derived average unabsorbed 0.5-4 keV flux is 1.13 (-0.13/+0.14) x 10^(-9) erg/s/cm^2. The uncertainties are quoted at the 90% confidence level for the above parameters. The Follow-up X-ray Telescope (FXT) on board EP observed this source autonomously about 4 min after T0, starting at 2025-05-12T11:23:44 (UTC). Within the WXT error circle, on-ground analysis of the FXT data found an uncatalogued source at R.A. = 215.2043, DEC = -10.1009 (J2000) with an uncertainty of 10 arcsec (radius, 90% C.L. statistical and systematic). During the observation a decline in the source flux lasting for a few hundred seconds is observed from the beginning. The averaged 0.5-10 keV FXT spectrum (from T0+291 s to T0+7094 s, with a total exposure time of 4,095 s) can be fitted by an absorbed power law model with a Galactic hydrogen column density of 5.7 x 10^20 cm^-2 and a photon index of 1.45 (+/-0.05). The derived average unabsorbed 0.5-10 keV flux is 3.78 (-0.18/+0.19) x 10^(-11) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. EP-FXT will continue monitoring this source. More follow-up observations are encouraged. The contact TAs of EP250512a are D. H. Zhao and H. N. Yang. Please contact them via email zhaodh(a)bao.ac.cn, hnyang(a)nao.cas.cn if needed. 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/40448. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38478] EP250512a/GRB 250512B: FTW optical and NIR observations of the counterpart
by GCN Circulars 13 May '25

13 May '25

TITLE: GCN CIRCULAR NUMBER: 40447 SUBJECT: EP250512a/GRB 250512B: FTW optical and NIR observations of the counterpart DATE: 25/05/13 03:20:43 GMT FROM: Malte Busmann at Ludwig-Maximilians-Universität München <m.busmann(a)physik.lmu.de> Malte Busmann (LMU), Brendan O’Connor (Carnegie Mellon U.), Daniel Gruen (LMU), and Antonella Palmese (Carnegie Mellon U.) report: We observed the couterpart of EP250512a/GRB 250512B (Zhao et al., GCN 40437; Maggi et al., GCN 40437; Li et al., GCN 40443; Xin et al., GCN 40444; Lipunov et al., GCN 40446) with the Three Channel Imager (3KK) at the Fraunhofer Telescope at Wendelstein Observatory (FTW) in the r, i and J band simultaneously for 10 x 180 s starting at 2025-05-12T21:43:13 UT (0.43 days after the trigger). We only detect the counterpart in the J band at J = (21.6 +/- 0.3) mag. The 3 sigma upper limits for the r and i band are r > 21.9 mag i > 21.2 mag. The r and i band magnitudes are calibrated against the PS1 catalog and the J band is calibrated with the 2MASS Catalog. All magnitudes are provided in the AB system and are not corrected for Galactic extinction. We thank Michael Schmidt from the Wendelstein Observatory staff for obtaining these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/40447. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38477] EP250512a: Global MASTER-Net observations report
by GCN Circulars 12 May '25

12 May '25

TITLE: GCN CIRCULAR NUMBER: 40446 SUBJECT: EP250512a: Global MASTER-Net observations report DATE: 25/05/12 20:45:41 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) was pointed to the EP250512a ( EP Team et al., GCN 40437) errorbox 28318 sec after notice time and 31541 sec after trigger time at 2025-05-12 20:07:49 UT, with upper limit up to 17.7 mag. The observations began at zenith distance = 30 deg. The sun altitude is -54.2 deg. The galactic latitude b = 46 deg., longitude l = 337 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2868623 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 31571 | 2025-05-12 20:07:49 | MASTER-SAAO | (14h 19m 12.13s , -10d 13m 30.1s) | C | 60 | 17.2 | 31631 | 2025-05-12 20:07:49 | MASTER-SAAO | (14h 19m 12.13s , -10d 13m 30.1s) | C | 180 | 17.7 | Coadd 31650 | 2025-05-12 20:09:08 | MASTER-SAAO | (14h 19m 06.91s , -10d 14m 28.5s) | C | 60 | 17.1 | 31730 | 2025-05-12 20:10:27 | MASTER-SAAO | (14h 19m 12.41s , -10d 13m 58.2s) | C | 60 | 17.2 | 31809 | 2025-05-12 20:11:47 | MASTER-SAAO | (14h 19m 09.57s , -10d 12m 28.8s) | C | 60 | 17.2 | 31869 | 2025-05-12 20:11:47 | MASTER-SAAO | (14h 19m 09.57s , -10d 12m 28.8s) | C | 180 | 17.6 | Coadd 31889 | 2025-05-12 20:13:06 | MASTER-SAAO | (14h 19m 09.61s , -10d 13m 58.7s) | C | 60 | 17.0 | 31968 | 2025-05-12 20:14:25 | MASTER-SAAO | (14h 19m 12.16s , -10d 12m 34.3s) | C | 60 | 17.0 | 32047 | 2025-05-12 20:15:44 | MASTER-SAAO | (14h 19m 07.13s , -10d 13m 22.0s) | C | 60 | 17.0 | 32107 | 2025-05-12 20:15:44 | MASTER-SAAO | (14h 19m 07.14s , -10d 13m 22.0s) | C | 180 | 17.6 | Coadd 32126 | 2025-05-12 20:17:04 | MASTER-SAAO | (14h 19m 05.72s , -10d 12m 20.9s) | C | 60 | 17.1 | 32206 | 2025-05-12 20:18:24 | MASTER-SAAO | (14h 19m 12.92s , -10d 13m 20.0s) | C | 60 | 17.2 | 32286 | 2025-05-12 20:19:43 | MASTER-SAAO | (14h 19m 06.56s , -10d 14m 18.8s) | C | 60 | 17.0 | 32346 | 2025-05-12 20:19:43 | MASTER-SAAO | (14h 19m 06.56s , -10d 14m 18.8s) | C | 180 | 17.5 | Coadd 32366 | 2025-05-12 20:21:04 | MASTER-SAAO | (14h 19m 13.61s , -10d 14m 04.5s) | C | 60 | 16.9 | 32446 | 2025-05-12 20:22:23 | MASTER-SAAO | (14h 19m 11.06s , -10d 12m 36.7s) | C | 60 | 17.0 | 32943 | 2025-05-12 20:30:40 | MASTER-SAAO | (14h 19m 12.88s , -10d 12m 10.3s) | C | 60 | 16.9 | 33003 | 2025-05-12 20:30:40 | MASTER-SAAO | (14h 19m 12.88s , -10d 12m 10.3s) | C | 180 | 17.4 | Coadd 33022 | 2025-05-12 20:32:00 | MASTER-SAAO | (14h 19m 18.93s , -10d 13m 09.3s) | C | 60 | 16.8 | 33102 | 2025-05-12 20:33:19 | MASTER-SAAO | (14h 19m 14.64s , -10d 14m 08.2s) | C | 60 | 16.8 | 33181 | 2025-05-12 20:34:39 | MASTER-SAAO | (14h 19m 21.08s , -10d 14m 06.4s) | C | 60 | 16.9 | 33241 | 2025-05-12 20:34:39 | MASTER-SAAO | (14h 19m 21.08s , -10d 14m 06.4s) | C | 180 | 17.5 | Coadd 33260 | 2025-05-12 20:35:58 | MASTER-SAAO | (14h 19m 18.22s , -10d 12m 20.5s) | C | 60 | 16.9 | 33340 | 2025-05-12 20:37:17 | MASTER-SAAO | (14h 19m 18.96s , -10d 14m 01.5s) | C | 60 | 16.8 | 33419 | 2025-05-12 20:38:37 | MASTER-SAAO | (14h 19m 22.19s , -10d 12m 23.8s) | C | 60 | 16.9 | 33499 | 2025-05-12 20:39:56 | MASTER-SAAO | (14h 19m 16.86s , -10d 13m 02.6s) | C | 60 | 16.8 | 33578 | 2025-05-12 20:41:16 | MASTER-SAAO | (14h 19m 18.30s , -10d 12m 01.7s) | C | 60 | 16.8 | 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/40446. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38476] EP250511a: FTW optical and NIR observations
by GCN Circulars 12 May '25

12 May '25

TITLE: GCN CIRCULAR NUMBER: 40445 SUBJECT: EP250511a: FTW optical and NIR observations DATE: 25/05/12 17:53:13 GMT FROM: Malte Busmann at Ludwig-Maximilians-Universität München <m.busmann(a)physik.lmu.de> Malte Busmann (LMU), Brendan O’Connor (Carnegie Mellon U.), Daniel Gruen (LMU), and Antonella Palmese (Carnegie Mellon U.) report: We observed the localization of EP250511a (Lian et al., GCN 40429; Li et al., GCN 40434) with the Three Channel Imager (3KK) at the Fraunhofer Telescope at Wendelstein Observatory (FTW) in the r, i and J band simultaneously for 10 x 180 s starting at 2025-05-11T21:30:13 UT (0.56 days after the trigger). We do not detect the counterpart (Schneider et al., GCN 40431; Li et al., GCN 40433) placing 3 sigma upper limits at r > 22.4 mag i > 22.0 mag J > 21.8 mag. These upper limits are consistent with the mentioned detections and previous upper limits (Perez-Garcia et al., GCN 40430; Lipunov et al., GCN 40432; Brivio et al., GCN 40435; Zhong et al., GCN 40442). The r and i band magnitudes are calibrated against the PS1 catalog and the J band is calibrated with the 2MASS Catalog. All magnitudes are provided in the AB system and are not corrected for Galactic extinction. We thank Michael Schmidt from the Wendelstein Observatory staff for obtaining these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/40445. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38475] GRB 250512B/EP250512a: SVOM/VT optical fading
by GCN Circulars 12 May '25

12 May '25

TITLE: GCN CIRCULAR NUMBER: 40444 SUBJECT: GRB 250512B/EP250512a: SVOM/VT optical fading DATE: 25/05/12 16:37:10 GMT FROM: Liping Xin at NAOC, SVOM <xlp(a)nao.cas.cn> L. P. Xin, H. L. Li, Y. L. Qiu, C. Wu, Z. H. Yao, 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), S. D. Vergani (CNRS, Obs. Paris/LUX), P. Maggi (ObAS), Y. N. Ma, D. H. Zhao (NAOC) report on behalf of the SVOM/VT Instrument Team: The analysis with more downlinked X-band data shows that the optical counterpart (Li et al., GCN 40443) of GRB 250512B/EP250512a (Maggi et al., GCN 40439, Zhao et al., GCN 40437) has been fading to about 21.5+/-0.2 (AB) mag in VT_R mag at the mid time of 1.6 hours after the burst, with an effective time of 12*50 seconds. The decay slop is about -1.0 after the peak time (Li et al., GCN 40443). 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/40444. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38474] GRB 250512B/EP250512a：SVOM/VT bright optical counterpart
by GCN Circulars 12 May '25

12 May '25

TITLE: GCN CIRCULAR NUMBER: 40443 SUBJECT: GRB 250512B/EP250512a：SVOM/VT bright optical counterpart DATE: 25/05/12 15:15:31 GMT FROM: Liping Xin at NAOC, SVOM <xlp(a)nao.cas.cn> H. L. Li, L. P. Xin, Y. L. Qiu, C. Wu, Z. H. Yao, 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), P. Maggi (ObAS), Y. N. Ma, D. H. Zhao(NAOC) report on behalf of the SVOM/VT Instrument Team: GRB 250512B (sb25051203), triggered both by SVOM/Eclairs (Maggi et al., GCN 40439) and Einstein Probe(EP/WXT) (labeled as EP250512a, Zhao et al., GCN 40437), was observed by on-board SVOM/VT after the automatic slew of the satellite. The VT conducted observations in the VT_B (400-650 nm) and VT_R (650-1000 nm) channels simultaneously. With the downlinked X-band data, the optical counterpart was clearly detected within the error box of EP/FXT(Zhao et al., GCN 40437) in both VT_B and VT_R bands. The earliest observation started on 2025-05-12T11:23:21 UTC (i.e. 193 seconds after the SVOM trigger time). The position of the counterpart is RA=215.20368 deg, DEC= -10.10071 deg, which is equivalent to: R.A.=14:20:48.88, DEC.=-10:06:02.56, J2000, Error=0.5 arcseconds The light curves show a brightening with a peak of 19.3+/-0.1 mag in VT_R and 21.0+/-0.2 mag in VT_B at 668 seconds after the burst. The photometry is in the AB system and is not corrected for Galactic extinction. Given the color of VT_B-VT_R~1.7 mag, it might be a low or intermediate redshift GRB (Wang et al., 2020). 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/40443. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38473] EP250511a: Mephisto optical upper limits
by GCN Circulars 12 May '25

12 May '25

TITLE: GCN CIRCULAR NUMBER: 40442 SUBJECT: EP250511a: Mephisto optical upper limits DATE: 25/05/12 14:58:06 GMT FROM: Brajesh Kumar at SWIFAR, YNU <brajesh(a)ynu.edu.cn> Shiyan Zhong, Jianhui Lian, Xufeng Zhu, Yicheng Jin, Dan Zhu, Guowang Du, Xingzhu Zou, Brajesh Kumar, Yuan Fang, Helong Guo, Yu Pan, Xinlei Chen, Jianghua Zhang, Edoardo P. Lagioia, Yuanpei Yang, Xiangkun Liu, Xiaowei Liu (all SWIFAR, YNU) report on behalf of the Mephisto Team: The field of EP250511a (Lian et al., GCN 40429) was observed with the 1.6-meter Multi-channel Photometric Survey Telescope (Mephisto) of Yunnan University, located at Lijiang Observatory. The simultaneous observations in Mephisto u/g/i bands were started from 2025-05-11T13:58:03 (~6 h after the trigger). The field was also simultaneously observed in v/r/z bands, starting from 2025-05-11T14:07:46. In our stacked u/g/i images and the single frame v/z images (r-band image was saturated due to high background of moon light), we did not detect any source at the position reported by Schneider et. al. (GCN 40431) and Li et al. (GCN 40433). The preliminary 3-sigma upper limits (listed below) are consistent with Perez-Garcia et al. (GCN 40430), Lipunov et al. (GCN 40432), and Brivio et al. (GCN 40435). Start_Time (UT) | Band | Exp(s) | LimMag(AB) --------------------|------|--------|------------- 2025-05-11T13:58:03 | u | 180*2 | > 19.965 2025-05-11T14:07:46 | v | 180*1 | > 19.152 2025-03-09T20:07:03 | g | 60+180 | > 19.876 2025-05-11T13:58:02 | i | 180*2 | > 19.810 2025-05-11T14:07:45 | z | 180*1 | > 18.032 ------------------------------------------------------------------------------------------------- Mephisto (Multi-channel Photometric Survey Telescope) is a 1.6-m wide-field multi-channel telescope, the first of its type in the world, capable of imaging the same field of view in three optical bands simultaneously. It provides real-time, high-quality colors of stellar objects. The on-site telescope assemblage and commissioning were carried out in September 2022. The first light in all three channels was achieved on 2023 December 21. ------------------------------------------------------------------------------------------------- View this GCN Circular online at https://gcn.nasa.gov/circulars/40442. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38472] GRB 250507B: GRBAlpha detection
by GCN Circulars 12 May '25

12 May '25

TITLE: GCN CIRCULAR NUMBER: 40441 SUBJECT: GRB 250507B: GRBAlpha detection DATE: 25/05/12 14:46:01 GMT FROM: Andras Pal at Konkoly Observatory <apal(a)szofi.net> A. Pal (Konkoly Observatory), M. Dafcikova, J. Ripa, N. Werner (Masaryk U.), M. Ohno, H. Takahashi (Hiroshima U.), L. Meszaros, B. Csak (Konkoly Observatory), N. Husarikova, F. Munz , M. Topinka, M. Duriskova, M. Kolar, L. Szakszonova, J.-P. Breuer, F. Hroch (Masaryk U.), T. Urbanec, M. Kasal, A. Povalac (Brno U. of Technology), J. Hudec, J. Kapus, M. Frajt (Spacemanic s.r.o), R. Laszlo, M. Koleda (Needronix s.r.o), M. Smelko, P. Hanak, P. Lipovsky (Technical U. of Kosice), G. Galgoczi (Wigner Research Center/Eotvos U.), Y. Uchida, H. Poon, H. Matake (Hiroshima U.), N. Uchida (ISAS/JAXA), T. Bozoki (Eotvos U.), G. Dalya (Eotvos U.), T. Enoto (Kyoto U.), Zs. Frei (Eotvos U.), G. Friss (Eotvos U.), Y. Fukazawa, K. Hirose (Hiroshima U.), S. Hisadomi (Nagoya U.), Y. Ichinohe (Rikkyo U.), K. Kapas (Eotvos U.), L. L. Kiss (Konkoly Observatory), T. Mizuno (Hiroshima U.), K. Nakazawa (Nagoya U.), H. Odaka (Univ of Tokyo), J. Takatsy (Eotvos U.), K. Torigoe (Hiroshima U.), N. Kogiso, M. Yoneyama (Osaka Metropolitan U.), M. Moritaki (U. Tokyo), T. Kano (U. Michigan) -- the GRBAlpha collaboration. We report a detection of a likely short-duration GRB 250507B by the GRBAlpha 1U CubeSat (Pal et al. 2023, A&A, 677, 40; https://ui.adsabs.harvard.edu/abs/2023A%26A...677A..40P/abstract). The event was also observed by Wind/Konus at the trigger time 2025-05-07 09:31:29.176 UTC. The GRBAlpha detection was confirmed at the peak time 2025-05-07 09:31:33.1 UTC. The T90 duration measured by GRBAlpha is 1.5 s and the overall significance during T90 reaches 13 sigma. The light curve obtained by GRBAlpha is available here: https://grbalpha.konkoly.hu/static/share/GRB250507B_GCN.pdf All GRBAlpha detections are listed at: https://monoceros.physics.muni.cz/hea/GRBAlpha/ GRBAlpha, launched on 2021 March 22, is a demonstration mission for a future CubeSat constellation (Werner et al. Proc. SPIE 2018). The detector of GRBAlpha consists of a 75 x 75 x 5 mm3 CsI scintillator read out by a SiPM array, covering the energy range from ~50 keV to ~1000 keV. To increase the duty cycle and the downlink rate, the upgrade of the on-board data acquisition software stack is in progress. The ground segment is also supported by the radio amateur community and it takes advantage of the SatNOGS network for increased data downlink volume. View this GCN Circular online at https://gcn.nasa.gov/circulars/40441. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38471] GRB 250506A: GRBAlpha detection
by GCN Circulars 12 May '25

12 May '25

TITLE: GCN CIRCULAR NUMBER: 40440 SUBJECT: GRB 250506A: GRBAlpha detection DATE: 25/05/12 14:45:14 GMT FROM: Andras Pal at Konkoly Observatory <apal(a)szofi.net> A. Pal (Konkoly Observatory), M. Dafcikova, J. Ripa, N. Werner (Masaryk U.), M. Ohno, H. Takahashi (Hiroshima U.), L. Meszaros, B. Csak (Konkoly Observatory), N. Husarikova, F. Munz , M. Topinka, M. Duriskova, M. Kolar, L. Szakszonova, J.-P. Breuer, F. Hroch (Masaryk U.), T. Urbanec, M. Kasal, A. Povalac (Brno U. of Technology), J. Hudec, J. Kapus, M. Frajt (Spacemanic s.r.o), R. Laszlo, M. Koleda (Needronix s.r.o), M. Smelko, P. Hanak, P. Lipovsky (Technical U. of Kosice), G. Galgoczi (Wigner Research Center/Eotvos U.), Y. Uchida, H. Poon, H. Matake (Hiroshima U.), N. Uchida (ISAS/JAXA), T. Bozoki (Eotvos U.), G. Dalya (Eotvos U.), T. Enoto (Kyoto U.), Zs. Frei (Eotvos U.), G. Friss (Eotvos U.), Y. Fukazawa, K. Hirose (Hiroshima U.), S. Hisadomi (Nagoya U.), Y. Ichinohe (Rikkyo U.), K. Kapas (Eotvos U.), L. L. Kiss (Konkoly Observatory), T. Mizuno (Hiroshima U.), K. Nakazawa (Nagoya U.), H. Odaka (Univ of Tokyo), J. Takatsy (Eotvos U.), K. Torigoe (Hiroshima U.), N. Kogiso, M. Yoneyama (Osaka Metropolitan U.), M. Moritaki (U. Tokyo), T. Kano (U. Michigan) -- the GRBAlpha collaboration. The long-duration GRB 250506A (Fermi/GBM detection: GCN 40355; SVOM/GRM and ECLAIRs detection: GCN 40358; GECAM-B detection: GCN 40396) was observed by the GRBAlpha 1U CubeSat (Pal et al. 2023, A&A, 677, 40; https://ui.adsabs.harvard.edu/abs/2023A%26A...677A..40P/abstract). The detection was confirmed at the peak time 2025-05-06 02:23:56.5 UTC. The T90 duration measured by GRBAlpha is 41 s and the overall significance during T90 reaches 22 sigma. The light curve obtained by GRBAlpha is available here: https://grbalpha.konkoly.hu/static/share/GRB250506A_GCN.pdf All GRBAlpha detections are listed at: https://monoceros.physics.muni.cz/hea/GRBAlpha/ GRBAlpha, launched on 2021 March 22, is a demonstration mission for a future CubeSat constellation (Werner et al. Proc. SPIE 2018). The detector of GRBAlpha consists of a 75 x 75 x 5 mm3 CsI scintillator read out by a SiPM array, covering the energy range from ~50 keV to ~1000 keV. To increase the duty cycle and the downlink rate, the upgrade of the on-board data acquisition software stack is in progress. The ground segment is also supported by the radio amateur community and it takes advantage of the SatNOGS network for increased data downlink volume. View this GCN Circular online at https://gcn.nasa.gov/circulars/40440. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38470] GRB 250512B: SVOM detection of a burst
by GCN Circulars 12 May '25

12 May '25

TITLE: GCN CIRCULAR NUMBER: 40439 SUBJECT: GRB 250512B: SVOM detection of a burst DATE: 25/05/12 14:40:03 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Pierre Maggi (ObAS), Yinuo Ma (NAOC), Nicolas Dagoneau (CEA), Ulysse Jacob (LUPM), Miguel Moita (CEA) report on behalf of the SVOM mission team: SVOM/ECLAIRs triggered and located GRB 250512B (SVOM burst-id sb25051203) starting at 2025-05-12T11:20:08 (Tb), also detected by Einstein Probe (labelled as EP250512a, Zhao et al. GCN 40437). The following trigger information was received after data download through the X-band ground station. The burst was detected onboard both by the Count-Rate Trigger (CRT) and the Image Trigger (IMT), which produced a sequence of 16 alerts. CRT provided the alert with the best signal-to-noise-ratio (SNR) of 25.26 in the 8-120 keV energy band over a time window of 20.40 seconds starting at Tb. The localization of the best alert is R.A., Dec. 215.22, -10.1086 degrees with a 90% confidence level (C.L.) radius of 3.65 arcmin (including systematic error of 2 arcmin added in quadrature). The ECLAIRs light curve in the 4-120 keV energy band shows a single broad peak structure with a T90 duration of 23.76 (-2.50/+0.48) seconds. SVOM slewed to the burst. MXT began observing the field at 2025-05-12T11:22:58.718 UTC, 160 seconds after Tb. Using the X-band data we found an uncatalogued X-ray source located at R.A., Dec. 215.200, -10.1128 degrees: R.A. (J2000) = 14h20m48.1s Dec. (J2000) = -10d06m46.16s with a 90% C.L. radius of 40 arcseconds including 35 arcseconds added in quadrature. This location is 1.2 arcminutes from the ECLAIRs onboard position and 50 arcseconds from the EP/FXT one. The MXT source is rapidly fading and is not detected in the second orbit starting 1.5 hours after slew. VT began observing the field after the slew. The analysis of the recorded images will be published in a future circular gathering information on the follow-up of the SVOM optical instruments. 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. MXT was developed jointly by CNES, CEA-IRFU, CNRS-IJCLab, University of Leicester, MPE. The Burst Advocate (BA) on shift for this burst is Pierre Maggi: pierre.maggi(a)astro.unistra.fr. Please contact the BA by email if you require additional information regarding the SVOM follow-up of this burst. View this GCN Circular online at https://gcn.nasa.gov/circulars/40439. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38469] GRB 250507B: SVOM/GRM observation of a burst
by GCN Circulars 12 May '25

12 May '25

TITLE: GCN CIRCULAR NUMBER: 40438 SUBJECT: GRB 250507B: SVOM/GRM observation of a burst DATE: 25/05/12 14:30:02 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: Olivier Godet, Hui Yang (IRAP) report on behalf of the SVOM team: SVOM/GRM was triggered in-flight by a burst GRB 250507B (SVOM trigger reference: sb25050704) at 2025-05-07T09:31:33.2 UTC (T0). 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 3.5 +0.9/-1.8 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb250507B.png ECLAIRs was not collecting data at the time of this burst. 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/40438. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38468] EP250512a: Einstein Probe detection of an X-ray transient
by GCN Circulars 12 May '25

12 May '25

TITLE: GCN CIRCULAR NUMBER: 40437 SUBJECT: EP250512a: Einstein Probe detection of an X-ray transient DATE: 25/05/12 12:13:33 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> D. H. Zhao, M. J. Liu, J. W. Hu, 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, designated EP250512a. The transient triggered EP-WXT (ID: 01709175718) at 2025-05-12T11:22:08 (UTC). The WXT position of the source is R.A. = 215.216 deg, DEC = -10.092 deg (J2000) with an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic). A follow-up observation with the Follow-up X-ray Telescope (FXT) was performed automatically. Within the WXT error circle, an uncatalogued X-ray source was detected at R.A. = 215.2023 deg, DEC = -10.0988 deg (J2000) with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic). Further information will be updated when the telemetry data is received. The contact TA of EP250512a is D. H. Zhao, please contact her via the email zhaodh(a)bao.ac.cn if needed. 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/40437. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38467] GRB 250512A: Fermi GBM Final Real-time Localization
by GCN Circulars 12 May '25

12 May '25

TITLE: GCN CIRCULAR NUMBER: 40436 SUBJECT: GRB 250512A: Fermi GBM Final Real-time Localization DATE: 25/05/12 12:12:11 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 12:01:36 UT on 12 May 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250512A (trigger 768744101.290912 / 250512501). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 318.9, Dec = 76.7 (J2000 degrees, equivalent to J2000 21h 15m, 76d 42'), with a statistical uncertainty of 9.5 degrees. The angle from the Fermi LAT boresight is 104.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250512501/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250512501/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250512501/… View this GCN Circular online at https://gcn.nasa.gov/circulars/40436. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38466] EP250511a: REM optical/NIR observations
by GCN Circulars 12 May '25

12 May '25

TITLE: GCN CIRCULAR NUMBER: 40435 SUBJECT: EP250511a: REM optical/NIR observations DATE: 25/05/12 09:02:36 GMT FROM: Riccardo Brivio at INAF-OAB <riccardo.brivio(a)inaf.it> R. Brivio, M. Ferro, P. D'Avanzo, S. Covino, D. Fugazza (INAF-OAB) report on behalf of the REM team: We observed the field of GRB EP250511a detected by EP/WXT (Lian et al., GCN 40429) with the REM 60 cm robotic telescope located at the ESO observatory of La Silla (Chile). The observations were carried in the g, r, i, z, J, H, and K bands, started on 2025 May 11 at 22:53:26 UT (i.e. 14.9 hr after the burst), and lasted for about 1 hour. From preliminary inspection, we do not detect any possible counterpart consistent with the candidate optical afterglow (Schneider et al., GCN 40431; Li et al., GCN 40433) down to the following 3sigma limits: r > 19.4 (AB; calibrated against the Pan-STARRS catalogue), at a mid-time of 15.3 hr after the trigger; H > 16.2 (Vega; calibrated against the 2MASS catalogue), at a mid-time of 15.0 hr after the trigger. View this GCN Circular online at https://gcn.nasa.gov/circulars/40435. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38465] EP250511a: Einstein Probe follow-up obsevation and refined analysis
by GCN Circulars 12 May '25

12 May '25

TITLE: GCN CIRCULAR NUMBER: 40434 SUBJECT: EP250511a: Einstein Probe follow-up obsevation and refined analysis DATE: 25/05/12 06:36:55 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> A. Li (BNU), Y. L. Wang (NAO, CAS), T. Y. Lian (NAO, CAS), C. C. Jin (NAO, CAS) behalf of the Einstein Probe (EP) team: The X-ray transient EP250511a was detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Lian et al., GCN 40429), and followed up by several telescopes (Perez-Garcia et al, GCN 40430; Schneider et al, GCN 40431; Lipunov et al, GCN 40432; Li et al, GCN 40433). Refined analysis of the WXT data shows that the event started at T0=2025-05-11T07:59:59 (UTC) and lasted for about 50s. The peak flux is about 3.8 x 10^(-9) erg/s/cm^2. The averaged 0.5-4 keV spectrum can be fitted by an absorbed power law model with a fixed Galactic hydrogen column density of 2.7 x 10^20 cm^-2 and a photon index of 2.17 (+/-0.71). The derived average unabsorbed 0.5-4 keV flux is 2.3 (-0.8/+0.6) x 10^(-10) erg/s/cm^2. The uncertainties are quoted at the 90% confidence level for the above parameters. The Follow-up X-ray Telescope (FXT) on board EP observed this source autonomously about 3 min after T0, starting at 2025-05-11T08:03:06 (UTC). Within the WXT error circle, on-ground analysis of the FXT data found an uncatalogued source at R.A. = 202.1113, DEC = -2.7023 (J2000) with an uncertainty of 10 arcsec (radius, 90% C.L. statistical and systematic). The averaged 0.5-10 keV FXT spectrum can be fitted by an absorbed power law model with a fixed Galactic hydrogen column density of 2.7 x 10^20 cm^-2 and a photon index of 2.98 (-0.59/+0.62). The derived average unabsorbed 0.5-10 keV flux is 1.7 (-0.7/+0.9) x 10^(-13) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. The contact TA of EP250511a is A. Li. Please contact him via email anli(a)mail.bnu.edu.cn if needed. 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/40434. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38464] EP250511a: SVOM/VT optical candidate comfirmation
by GCN Circulars 12 May '25

12 May '25

TITLE: GCN CIRCULAR NUMBER: 40433 SUBJECT: EP250511a: SVOM/VT optical candidate comfirmation DATE: 25/05/12 01:50:53 GMT FROM: Huali Li at at NAOC, SVOM <lhl(a)nao.cas.cn> H. L. Li, L. P. Xin, Y. L. Qiu, J. Wang, C. Wu, Z. H. Yao, Y. N. Ma, X. H. Han, Y. Xu, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. S. Deng, J. Y. Wei, T. Y. Lian (NAOC), A. Li (BNU), Y. L. Wang (NAOC; ICE, CSIC-IEEC), C. C. Jin (NAOC) report on behalf of the SVOM and Einstein Probe (EP) teams: SVOM/VT observed the X-ray transient EP250511a (Lian et al., GCN 40429) in ToO mode in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. The observations started at 2025-05-11T15:46:49 UT, about 7.78 hours after the trigger. The candidate reported by Bchneider et al. (GCN 40431) within the error box of EP/FXT (Lian et al., GCN 40429) was clearly detected by VT in both channels. The brightness of the candidate was derived as below : Mid-time Band mag(AB) exposure 8.16 hour VT_B 22.41 +/- 0.13 36*70 sec 8.14 hour VT_R 22.29 +/- 0.13 36*70 sec 9.77 hour VT_B 22.65 +/- 0.15 37*70 sec 9.78 hour VT_R 22.52 +/- 0.16 37*70 sec Our photometry was estimated in AB magnitude and 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/40433. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38463] EP250511a: Global MASTER-Net observations report
by GCN Circulars 11 May '25

11 May '25

TITLE: GCN CIRCULAR NUMBER: 40432 SUBJECT: EP250511a: Global MASTER-Net observations report DATE: 25/05/11 20:36:40 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) was pointed to the EP250511a ( EP Team et al., GCN 40429) errorbox 28887 sec after notice time and 44100 sec after trigger time at 2025-05-11 20:14:59 UT, with upper limit up to 16.9 mag. The observations began at zenith distance = 30 deg. The sun altitude is -55.6 deg. The galactic latitude b = 58 deg., longitude l = 322 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2867812 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 44115 | 2025-05-11 20:14:59 | MASTER-SAAO | (13h 27m 09.60s , -02d 50m 52.7s) | C | 30 | 16.8 | 44220 | 2025-05-11 20:14:59 | MASTER-SAAO | (13h 27m 09.60s , -02d 50m 52.5s) | C | 240 | 16.8 | Coadd 44165 | 2025-05-11 20:15:48 | MASTER-SAAO | (13h 27m 07.01s , -02d 49m 12.4s) | C | 30 | 16.9 | 44259 | 2025-05-11 20:16:38 | MASTER-SAAO | (13h 27m 08.05s , -02d 50m 48.6s) | C | 120 | 16.7 | 44399 | 2025-05-11 20:18:57 | MASTER-SAAO | (13h 27m 12.36s , -02d 49m 05.6s) | C | 120 | 16.8 | 44538 | 2025-05-11 20:21:16 | MASTER-SAAO | (13h 27m 08.49s , -02d 49m 44.1s) | C | 120 | 16.6 | 44707 | 2025-05-11 20:23:36 | MASTER-SAAO | (13h 27m 08.91s , -02d 48m 40.9s) | C | 180 | 15.3 | 44907 | 2025-05-11 20:26:55 | MASTER-SAAO | (13h 27m 18.75s , -02d 49m 37.8s) | C | 180 | 16.1 | 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/40432. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38462] EP250511a: COLIBRÍ optical counterpart candidate
by GCN Circulars 11 May '25

11 May '25

TITLE: GCN CIRCULAR NUMBER: 40431 SUBJECT: EP250511a: COLIBRÍ optical counterpart candidate DATE: 25/05/11 14:01:49 GMT FROM: Benjamin Schneider at MIT <bschn(a)mit.edu> Benjamin Schneider (LAM), Kin Ocelotl López (UNAM), Rosa L. Becerra (U Roma), Camila Angulo (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Fredd Alvarez (UNAM), Jean-Luc Atteia (IRAP), Dalya Akl (AUS), Sarah Antier (OCA), Nathaniel R. Butler (ASU) , Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Noémie Globus (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), and Antonio de Ugarte Postigo (LAM): We imaged the field of the EP250511a (Lian et al., GCN Circ. 40429) using the DDRAGO wide-field imager on the COLIBRÍ telescope. We observed from 2025-05-11 09:25:48 to 10:08:02 UTC (from 1.43 to 2.13 hours after the trigger, and 2 minutes after the notice) and obtained 32 minutes of exposure in the i filter. The data were reduced and coadded with the COLIBRÍ pipeline and analyzed with STDWeb/STDPipe (Karpov 2025). The photometry was calibrated using nearby stars from the PanSTARRS catalog, is in the AB system, and is not corrected for Galactic extinction. We marginally detect a new source consistent with the FXT position (Lian et al., GCN Circ. 40429) and not visible in PanSTARRS at: RA(J2000) = 13:28:26.68 = 202.1111 degrees Dec(J2000) = -2:42:11.1 = -2.7030 degrees with an uncertainty of 0.5 arcsec. The preliminary magnitude derived for that source is: i ~ 21.9 We note the presence of a possible host galaxy in deeper Legacy Survey images, located 0.5 arcsec from the optical counterpart candidate, with magnitudes of g = 23.61 +/- 0.04 and r = 23.67 +/- 0.05. 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/40431. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38461] EP250511a: BOOTES-5 optical upper limit
by GCN Circulars 11 May '25

11 May '25

TITLE: GCN CIRCULAR NUMBER: 40430 SUBJECT: EP250511a: BOOTES-5 optical upper limit DATE: 25/05/11 12:27:11 GMT FROM: I. Perez-Garcia at Institute of Astrophysics of Andalusia <ipg(a)iaa.es> I. Perez-Garcia, E. J. Fernandez-Garcia, M. D. Caballero-Garcia, S.-Y. Wu, R. Sanchez-Ramirez, S. Guziy and A. J. Castro-Tirado (IAA-CSIC, Granada), I. M. Carrasco (SMA), M. Gritsevich (Univ. of Helsinki), C. Perez del Pulgar (Univ. of Malaga), Y.-D. Hu (GXU), S. Jeong (ADD, Daejeon), G. Garcia-Segura and D. Hiriart (IA-UNAM, Ensenada), D. R. Xiong (Yunnan Observatories of CAS, Kunming), and W. H. Lee (UNAM, Mexico DF), on behalf of a larger collaboration, report: Following the detection of EP250511a by EP (Lian et al., GCNC [40429](https://gcn.nasa.gov/circulars/40429)), the 0.6m BOOTES-5/JGU robotic telescope at San Pedro Martir Observatory (Mexico) automatically responded to this high-energy event starting on May 11, 09:22:17 UT (i.e. 1.3 hours after detection and 1 min after notification). No optical transient is detected down to 18.2 mag (clear filter). We would like to thank the staff at San Pedro Martir Observatory for their excellent support. View this GCN Circular online at https://gcn.nasa.gov/circulars/40430. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38460] EP250511a: Einstein Probe detection of an X-ray transient
by GCN Circulars 11 May '25

11 May '25

TITLE: GCN CIRCULAR NUMBER: 40429 SUBJECT: EP250511a: Einstein Probe detection of an X-ray transient DATE: 25/05/11 12:09:26 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> T. Y. Lian (NAO, CAS), A. Li (BNU), Y. L. Wang (NAO, CAS; ICE, CSIC-IEEC), C. C. Jin (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 EP250511a. The transient triggered EP-WXT (ID: 01709175648) at 2025-05-11T07:59:59 (UTC). The WXT position of the source is R.A. = 202.096 deg, DEC = -2.725 deg (J2000) with an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic). A follow-up observation with the Follow-up X-ray Telescope (FXT) was performed automatically. Within the WXT error circle, an uncatalogued X-ray source was detected at R.A. = 202.1113 deg, DEC = -2.7023 deg (J2000) with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic). Further information will be updated when the telemetry data is received. Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). View this GCN Circular online at https://gcn.nasa.gov/circulars/40429. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38459] EP250508a: Gemini NIR upper limits
by GCN Circulars 11 May '25

11 May '25

TITLE: GCN CIRCULAR NUMBER: 40428 SUBJECT: EP250508a: Gemini NIR upper limits DATE: 25/05/11 07:27:31 GMT FROM: Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani(a)nbi.ku.dk> A. J. Levan (Radboud and Warwick), J. C. Rastinejad (Northwestern), A. Martin-Carrillo (UCD), J. A. Quirola-Vasquez (Radboud), F. E. Bauer (SSI and UTA), G. Corcoran (UCD), R. A. J. Eyles-Ferris (Leicester), P. G. Jonker (Radboud), D. B. Malesani (DAWN/NBI and Radboud), report on behalf of a larger collaboration: We observed the field of the fast X-ray transient EP250508a (Liang et al., GCN 40390; Zhao et al., GCN 40399) using the Gemini-South telescope equipped with the FLAMINGOS-2 near-infrared imager (program GS-2025A-FT-106, PI Bauer). Observations were started on 2025 May 9 at 02:08:01 UT (20.07 hr after the EP trigger), and we secured 9 and 4.8 min imaging in the J and Ks bands, respectively. The seeing was modest at ~1.7" in the J-band image. No source is detected at the coordinates of the optical afterglow reported by SVOM/VT (Xin et al., GCN 40402; Li et al., GCN 40412), down to 5-sigma limiting magnitudes: J > 22.9 (AB system, 20.28 hr after trigger); Ks > 22.2 (AB system, 22.58 hr after trigger). These upper limits were calibrated using nearby stars from the VISTA Hemisphere Survey (VHS) catalogue. We thank excellent support from the observing staff at Gemini, in particular Venu Kalari and Henrique Reggiani. View this GCN Circular online at https://gcn.nasa.gov/circulars/40428. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38458] GRB 250510B: Fermi GBM Observation
by GCN Circulars 11 May '25

11 May '25

TITLE: GCN CIRCULAR NUMBER: 40427 SUBJECT: GRB 250510B: Fermi GBM Observation DATE: 25/05/11 05:33:44 GMT FROM: A. Holzmann Airasca at University of Trento and INFN Bari <a.holzmannairasca(a)unitn.it> A. Holzmann Airasca (UniTrento and INFN Bari) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 06:41:54.06 UT on 10 May 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250510B (trigger 768552119/250510279). which was also detected by Swift/BAT-GUANO (S. Ronchini et al. 2025, GCN 40419). The Fermi GBM on-ground location is consistent with the Swift/BAT-GUANO position. The angle from the Fermi LAT boresight is 103 degrees. The GBM light curve consists of main emission episode with a duration (T90) of about 35 s (50-300 keV). The time-averaged spectrum from T0+0.51 to T0+35.58 s is best fit by a Band function with Epeak = 147 +/- 15 keV, alpha = 0.71 +/- 0.38, and beta = -2.79 +/- 0.49. The event fluence (10-1000 keV) in this time interval is (4.79 +/- 0.32)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0+2.01 s in the 10-1000 keV band is 2.44 +/- 0.22 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/40427. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38457] Fermi GRB 250510C: Global MASTER-Net observations report
by GCN Circulars 11 May '25

11 May '25

TITLE: GCN CIRCULAR NUMBER: 40426 SUBJECT: Fermi GRB 250510C: Global MASTER-Net observations report DATE: 25/05/11 01:32:21 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 250510C ( Fermi GBM team, GCN 40424) errorbox 2642 sec after notice time and 2680 sec after trigger time at 2025-05-10 22:57:20 UT, with upper limit up to 19.5 mag. Observations started at twilight. The observations began at zenith distance = 41 deg. The sun altitude is -14.5 deg. The galactic latitude b = 29 deg., longitude l = 212 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2867339 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 2700 | 2025-05-10 22:57:20 | MASTER-OAFA | (09h 07m 31.64s , +09d 29m 09.5s) | C | 40 | 17.4 | 2710 | 2025-05-10 22:57:20 | MASTER-OAFA | (08h 58m 15.88s , +09d 06m 34.4s) | C | 60 | 19.3 | 2778 | 2025-05-10 22:58:38 | MASTER-OAFA | (09h 05m 01.80s , +07d 33m 46.8s) | C | 40 | 17.7 | 2788 | 2025-05-10 22:58:38 | MASTER-OAFA | (08h 55m 48.52s , +07d 11m 15.2s) | C | 60 | 19.4 | 2857 | 2025-05-10 22:59:56 | MASTER-OAFA | (08h 47m 55.47s , +05d 41m 08.9s) | C | 40 | 17.5 | 2867 | 2025-05-10 22:59:57 | MASTER-OAFA | (08h 38m 44.26s , +05d 18m 40.5s) | C | 60 | 19.1 | 2940 | 2025-05-10 23:01:20 | MASTER-OAFA | (09h 03m 07.27s , +05d 40m 38.9s) | C | 40 | 17.5 | 2951 | 2025-05-10 23:01:20 | MASTER-OAFA | (08h 53m 55.86s , +05d 18m 11.4s) | C | 60 | 19.2 | 3020 | 2025-05-10 23:02:40 | MASTER-OAFA | (09h 20m 18.53s , +07d 35m 47.0s) | C | 40 | 17.6 | 3030 | 2025-05-10 23:02:40 | MASTER-OAFA | (09h 11m 04.97s , +07d 13m 14.9s) | C | 60 | 19.3 | 3100 | 2025-05-10 23:03:59 | MASTER-OAFA | (08h 46m 42.34s , +03d 46m 36.1s) | C | 40 | 17.5 | 3110 | 2025-05-10 23:04:00 | MASTER-OAFA | (08h 37m 32.42s , +03d 24m 11.6s) | C | 60 | 19.1 | 3179 | 2025-05-10 23:05:18 | MASTER-OAFA | (09h 22m 52.75s , +09d 27m 55.7s) | C | 40 | 17.7 | 3189 | 2025-05-10 23:05:19 | MASTER-OAFA | (09h 13m 36.67s , +09d 05m 18.5s) | C | 60 | 19.3 | 3258 | 2025-05-10 23:06:38 | MASTER-OAFA | (09h 01m 57.14s , +03d 45m 59.4s) | C | 40 | 17.5 | 3268 | 2025-05-10 23:06:38 | MASTER-OAFA | (08h 52m 46.93s , +03d 23m 35.1s) | C | 60 | 19.2 | 3337 | 2025-05-10 23:07:57 | MASTER-OAFA | (09h 07m 31.37s , +09d 29m 55.9s) | C | 40 | 17.7 | 3347 | 2025-05-10 23:07:57 | MASTER-OAFA | (08h 58m 15.39s , +09d 07m 18.0s) | C | 60 | 19.4 | 3413 | 2025-05-10 23:09:13 | MASTER-OAFA | (09h 05m 01.60s , +07d 34m 02.9s) | C | 40 | 17.9 | 3424 | 2025-05-10 23:09:13 | MASTER-OAFA | (08h 55m 48.24s , +07d 11m 29.4s) | C | 60 | 19.4 | 3591 | 2025-05-10 23:12:10 | MASTER-OAFA | (08h 47m 50.34s , +05d 40m 45.5s) | C | 40 | 17.4 | 3601 | 2025-05-10 23:12:11 | MASTER-OAFA | (08h 38m 39.27s , +05d 18m 17.8s) | C | 60 | 19.0 | 3668 | 2025-05-10 23:13:28 | MASTER-OAFA | (09h 03m 06.64s , +05d 41m 53.6s) | C | 40 | 17.6 | 3678 | 2025-05-10 23:13:28 | MASTER-OAFA | (08h 53m 55.34s , +05d 19m 26.2s) | C | 60 | 19.3 | 3745 | 2025-05-10 23:14:45 | MASTER-OAFA | (09h 20m 24.61s , +07d 35m 03.9s) | C | 40 | 17.7 | 3756 | 2025-05-10 23:14:45 | MASTER-OAFA | (09h 11m 11.20s , +07d 12m 32.1s) | C | 60 | 19.3 | 3824 | 2025-05-10 23:16:03 | MASTER-OAFA | (08h 46m 35.12s , +03d 45m 49.5s) | C | 40 | 17.4 | 3834 | 2025-05-10 23:16:04 | MASTER-OAFA | (08h 37m 25.39s , +03d 23m 25.1s) | C | 60 | 19.1 | 3903 | 2025-05-10 23:17:22 | MASTER-OAFA | (09h 22m 58.02s , +09d 28m 41.5s) | C | 40 | 17.8 | 3913 | 2025-05-10 23:17:23 | MASTER-OAFA | (09h 13m 42.06s , +09d 06m 04.1s) | C | 60 | 19.4 | 3980 | 2025-05-10 23:18:40 | MASTER-OAFA | (09h 01m 52.76s , +03d 47m 45.9s) | C | 40 | 17.5 | 3991 | 2025-05-10 23:18:40 | MASTER-OAFA | (08h 52m 42.75s , +03d 25m 21.4s) | C | 60 | 19.3 | 4058 | 2025-05-10 23:19:57 | MASTER-OAFA | (09h 07m 30.76s , +09d 28m 27.1s) | C | 40 | 17.7 | 4068 | 2025-05-10 23:19:58 | MASTER-OAFA | (08h 58m 15.02s , +09d 05m 48.6s) | C | 60 | 19.5 | 4134 | 2025-05-10 23:21:13 | MASTER-OAFA | (09h 05m 04.47s , +07d 36m 06.6s) | C | 40 | 17.7 | 4144 | 2025-05-10 23:21:14 | MASTER-OAFA | (08h 55m 51.28s , +07d 13m 32.5s) | C | 60 | 19.4 | 4308 | 2025-05-10 23:24:07 | MASTER-OAFA | (08h 47m 48.67s , +05d 41m 58.8s) | C | 40 | 17.4 | 4318 | 2025-05-10 23:24:08 | MASTER-OAFA | (08h 38m 37.81s , +05d 19m 30.8s) | C | 60 | 18.9 | 4384 | 2025-05-10 23:25:24 | MASTER-OAFA | (09h 03m 10.75s , +05d 41m 08.5s) | C | 40 | 17.6 | 4394 | 2025-05-10 23:25:24 | MASTER-OAFA | (08h 53m 59.66s , +05d 18m 40.7s) | C | 60 | 19.1 | 4462 | 2025-05-10 23:26:42 | MASTER-OAFA | (09h 20m 16.31s , +07d 34m 20.1s) | C | 40 | 17.7 | 4473 | 2025-05-10 23:26:42 | MASTER-OAFA | (09h 11m 03.06s , +07d 11m 48.3s) | C | 60 | 19.2 | 4540 | 2025-05-10 23:28:00 | MASTER-OAFA | (08h 46m 41.42s , +03d 46m 01.9s) | C | 40 | 17.4 | 4551 | 2025-05-10 23:28:00 | MASTER-OAFA | (08h 37m 31.90s , +03d 23m 37.4s) | C | 60 | 19.0 | 4618 | 2025-05-10 23:29:18 | MASTER-OAFA | (09h 22m 54.00s , +09d 30m 22.2s) | C | 40 | 17.7 | 4628 | 2025-05-10 23:29:18 | MASTER-OAFA | (09h 13m 38.12s , +09d 07m 44.9s) | C | 60 | 19.3 | 4698 | 2025-05-10 23:30:38 | MASTER-OAFA | (09h 01m 52.32s , +03d 46m 19.6s) | C | 40 | 17.5 | 4708 | 2025-05-10 23:30:38 | MASTER-OAFA | (08h 52m 42.51s , +03d 23m 55.4s) | C | 60 | 19.1 | 4775 | 2025-05-10 23:31:55 | MASTER-OAFA | (09h 07m 33.62s , +09d 30m 04.9s) | C | 40 | 17.7 | 4785 | 2025-05-10 23:31:55 | MASTER-OAFA | (08h 58m 18.00s , +09d 07m 26.7s) | C | 60 | 19.4 | 4851 | 2025-05-10 23:33:11 | MASTER-OAFA | (09h 04m 57.09s , +07d 35m 27.3s) | C | 40 | 17.7 | 4862 | 2025-05-10 23:33:11 | MASTER-OAFA | (08h 55m 44.10s , +07d 12m 53.4s) | C | 60 | 19.3 | 4930 | 2025-05-10 23:34:30 | MASTER-OAFA | (08h 47m 54.19s , +05d 41m 14.7s) | C | 40 | 17.4 | 4941 | 2025-05-10 23:34:30 | MASTER-OAFA | (08h 38m 43.41s , +05d 18m 44.8s) | C | 60 | 19.0 | 5007 | 2025-05-10 23:35:46 | MASTER-OAFA | (09h 03m 05.73s , +05d 40m 24.1s) | C | 40 | 17.5 | 5017 | 2025-05-10 23:35:47 | MASTER-OAFA | (08h 53m 54.69s , +05d 17m 55.3s) | C | 60 | 19.1 | 5083 | 2025-05-10 23:37:03 | MASTER-OAFA | (09h 20m 23.31s , +07d 34m 43.4s) | C | 40 | 17.7 | 5094 | 2025-05-10 23:37:03 | MASTER-OAFA | (09h 11m 10.07s , +07d 12m 10.4s) | C | 60 | 19.1 | 5162 | 2025-05-10 23:38:22 | MASTER-OAFA | (08h 46m 38.03s , +03d 47m 57.1s) | C | 40 | 17.3 | 5173 | 2025-05-10 23:38:22 | MASTER-OAFA | (08h 37m 28.61s , +03d 25m 31.9s) | C | 60 | 18.9 | 5242 | 2025-05-10 23:39:41 | MASTER-OAFA | (09h 22m 53.54s , +09d 28m 45.0s) | C | 40 | 17.7 | 5252 | 2025-05-10 23:39:42 | MASTER-OAFA | (09h 13m 37.77s , +09d 06m 07.3s) | C | 60 | 19.3 | 5320 | 2025-05-10 23:41:00 | MASTER-OAFA | (09h 01m 54.38s , +03d 48m 23.7s) | C | 40 | 17.5 | 5330 | 2025-05-10 23:41:00 | MASTER-OAFA | (08h 52m 44.67s , +03d 25m 59.0s) | C | 60 | 19.0 | 5398 | 2025-05-10 23:42:17 | MASTER-OAFA | (09h 07m 27.75s , +09d 29m 44.3s) | C | 40 | 17.7 | 5408 | 2025-05-10 23:42:18 | MASTER-OAFA | (08h 58m 12.26s , +09d 07m 06.1s) | C | 60 | 19.3 | 5473 | 2025-05-10 23:43:33 | MASTER-OAFA | (09h 04m 56.34s , +07d 36m 39.5s) | C | 40 | 17.7 | 5484 | 2025-05-10 23:43:33 | MASTER-OAFA | (08h 55m 43.45s , +07d 14m 05.6s) | C | 60 | 19.2 | 5552 | 2025-05-10 23:44:51 | MASTER-OAFA | (08h 47m 49.09s , +05d 40m 24.5s) | C | 40 | 17.4 | 5562 | 2025-05-10 23:44:52 | MASTER-OAFA | (08h 38m 38.50s , +05d 17m 55.0s) | C | 60 | 18.9 | 5628 | 2025-05-10 23:46:08 | MASTER-OAFA | (09h 03m 11.45s , +05d 40m 56.4s) | C | 40 | 17.6 | 5639 | 2025-05-10 23:46:08 | MASTER-OAFA | (08h 54m 00.57s , +05d 18m 27.8s) | C | 60 | 19.1 | 5705 | 2025-05-10 23:47:25 | MASTER-OAFA | (09h 20m 19.52s , +07d 36m 39.8s) | C | 40 | 17.7 | 5715 | 2025-05-10 23:47:25 | MASTER-OAFA | (09h 11m 06.40s , +07d 14m 07.2s) | C | 60 | 19.3 | 5783 | 2025-05-10 23:48:43 | MASTER-OAFA | (08h 46m 37.72s , +03d 46m 50.6s) | C | 40 | 17.4 | 5794 | 2025-05-10 23:48:43 | MASTER-OAFA | (08h 37m 28.49s , +03d 24m 25.9s) | C | 60 | 18.9 | 5861 | 2025-05-10 23:50:01 | MASTER-OAFA | (09h 22m 56.76s , +09d 30m 53.4s) | C | 40 | 17.7 | 5872 | 2025-05-10 23:50:01 | MASTER-OAFA | (09h 13m 41.10s , +09d 08m 16.1s) | C | 60 | 19.3 | 5938 | 2025-05-10 23:51:18 | MASTER-OAFA | (09h 01m 47.87s , +03d 47m 35.9s) | C | 40 | 17.5 | 5948 | 2025-05-10 23:51:18 | MASTER-OAFA | (08h 52m 38.34s , +03d 25m 12.0s) | C | 60 | 19.1 | 6015 | 2025-05-10 23:52:35 | MASTER-OAFA | (09h 07m 26.39s , +09d 30m 55.0s) | C | 40 | 17.8 | 6025 | 2025-05-10 23:52:35 | MASTER-OAFA | (08h 58m 11.05s , +09d 08m 17.2s) | C | 60 | 19.2 | 6091 | 2025-05-10 23:53:51 | MASTER-OAFA | (09h 05m 02.19s , +07d 35m 49.1s) | C | 40 | 17.7 | 6101 | 2025-05-10 23:53:51 | MASTER-OAFA | (08h 55m 49.50s , +07d 13m 15.9s) | C | 60 | 19.2 | 6170 | 2025-05-10 23:55:09 | MASTER-OAFA | (08h 47m 54.28s , +05d 41m 01.5s) | C | 40 | 17.3 | 6180 | 2025-05-10 23:55:10 | MASTER-OAFA | (08h 38m 43.87s , +05d 18m 32.7s) | C | 60 | 18.8 | 6248 | 2025-05-10 23:56:27 | MASTER-OAFA | (09h 03m 07.31s , +05d 42m 40.8s) | C | 40 | 17.5 | 6258 | 2025-05-10 23:56:28 | MASTER-OAFA | (08h 53m 56.59s , +05d 20m 12.5s) | C | 60 | 19.0 | 6324 | 2025-05-10 23:57:44 | MASTER-OAFA | (09h 20m 19.06s , +07d 35m 12.4s) | C | 40 | 17.6 | 6335 | 2025-05-10 23:57:44 | MASTER-OAFA | (09h 11m 06.13s , +07d 12m 40.5s) | C | 60 | 19.1 | 6404 | 2025-05-10 23:59:04 | MASTER-OAFA | (08h 46m 40.91s , +03d 48m 01.2s) | C | 40 | 17.2 | 6414 | 2025-05-10 23:59:04 | MASTER-OAFA | (08h 37m 31.88s , +03d 25m 36.7s) | C | 60 | 18.8 | 6483 | 2025-05-11 00:00:22 | MASTER-OAFA | (09h 22m 49.32s , +09d 30m 08.6s) | C | 40 | 17.6 | 6493 | 2025-05-11 00:00:23 | MASTER-OAFA | (09h 13m 33.80s , +09d 07m 31.7s) | C | 60 | 19.2 | 6565 | 2025-05-11 00:01:45 | MASTER-OAFA | (09h 01m 48.71s , +03d 48m 44.6s) | C | 40 | 17.5 | 6575 | 2025-05-11 00:01:45 | MASTER-OAFA | (08h 52m 39.36s , +03d 26m 20.8s) | C | 60 | 19.0 | 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/40426. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38456] Fermi GRB 250510B: Global MASTER-Net observations report
by GCN Circulars 11 May '25

11 May '25

TITLE: GCN CIRCULAR NUMBER: 40425 SUBJECT: Fermi GRB 250510B: Global MASTER-Net observations report DATE: 25/05/11 01:31:12 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 250510B ( Fermi GBM team, GCN 40418) errorbox 62438 sec after notice time and 62477 sec after trigger time at 2025-05-11 00:03:11 UT, with upper limit up to 19.0 mag. The observations began at zenith distance = 27 deg. The sun altitude is -28.5 deg. The galactic latitude b = 9 deg., longitude l = 250 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2866812 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 62497 | 2025-05-11 00:03:11 | MASTER-OAFA | (08h 43m 33.97s , -26d 38m 01.3s) | C | 40 | 17.5 | 62508 | 2025-05-11 00:03:11 | MASTER-OAFA | (08h 33m 17.64s , -26d 59m 17.6s) | C | 60 | 18.8 | 62575 | 2025-05-11 00:04:28 | MASTER-OAFA | (08h 51m 56.95s , -24d 43m 41.9s) | C | 40 | 17.6 | 62585 | 2025-05-11 00:04:29 | MASTER-OAFA | (08h 41m 50.32s , -25d 05m 00.8s) | C | 60 | 19.0 | 62653 | 2025-05-11 00:05:47 | MASTER-OAFA | (08h 35m 04.55s , -24d 42m 42.7s) | C | 40 | 17.6 | 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/40425. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38455] GRB 250510C: Fermi GBM Final Real-time Localization
by GCN Circulars 10 May '25

10 May '25

TITLE: GCN CIRCULAR NUMBER: 40424 SUBJECT: GRB 250510C: Fermi GBM Final Real-time Localization DATE: 25/05/10 22:23:13 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 22:12:40 UT on 10 May 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250510C (trigger 768607965.139286 / 250510925). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 127.9, Dec = 13.4 (J2000 degrees, equivalent to J2000 08h 31m, 13d 24'), with a statistical uncertainty of 12.8 degrees. The angle from the Fermi LAT boresight is 15.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250510925/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250510925/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250510925/… View this GCN Circular online at https://gcn.nasa.gov/circulars/40424. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38454] GRB 250510A: Swift-XRT observations
by GCN Circulars 10 May '25

10 May '25

TITLE: GCN CIRCULAR NUMBER: 40423 SUBJECT: GRB 250510A: Swift-XRT observations DATE: 25/05/10 16:54:51 GMT FROM: Simone Dichiara at Pennsylvania State University <sbd5667(a)psu.edu> S. Dichiara (PSU), K.L. Page (U. Leicester), J.A. Kennea (PSU), P. D'Avanzo (INAF-OAB), M.G. Bernardini (INAF-OAB), E. Ambrosi (INAF-IASFPA) , M. A. Williams (PSU), J.P. Osborne (U. Leicester), A.P. Beardmore (U. Leicester) and P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team: We have analysed 1.8 ks of XRT data for GRB 250510A, from 10.2 ks to 20.8 ks after the SVOM/ECLAIRs trigger. The data are entirely in Photon Counting (PC) mode. Within the SVOM/ECLAIRs 90% C.L. error region (GCN #40415) we detect the EP-FXT source EPF_J185624.8+181937 (GCN#40420) at RA, Dec = 284.10364, +18.3267 which is equivalent to: RA (J2000): 18h 56m 24.87s Dec (J2000): +18d 19′ 36.0″ with an uncertainty of 5.7 arcsec (radius, 90% confidence). The source has a mean count rate of 7.3e-03 ct/sec and a flux of 3.2 (+1.3, -1.1) × 10^-13 erg cm^-2 s^-1 (0.3-10 keV); we note that this position is also consistent with a known 2MASS source, 2MASS J18562485+1819380. No other X-ray sources have been detected. The 3-sigma upper limit in the field ranges from ~4.4e-03 to ~1.0e-02 ct s^-1, corresponding to a 0.3-10 keV observed flux of 1.9e-13 to 4.4e-13 erg cm^-2 s^-1 (assuming a typical GRB spectrum). The results of the XRT-team automatic analysis are available at https://www.swift.ac.uk/SVOM/SVOM_FIELD00016/. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/40423. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38453] GRB 250509A: Fermi GBM Observation
by GCN Circulars 10 May '25

10 May '25

TITLE: GCN CIRCULAR NUMBER: 40422 SUBJECT: GRB 250509A: Fermi GBM Observation DATE: 25/05/10 16:51:18 GMT FROM: Ava Myers at NASA GSFC <ava.myers(a)nasa.gov> A. Myers (NPP/GSFC), C. Meegan (UAH) and A. Holzmann Airasca (UniTrento and INFN Bari) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 22:33:29.29 UT on 09 May 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250509A (trigger 768522814/250509940). which was also detected by Swift BAT (M. H. Siegel et al. 2025, GCN 40407). The Fermi GBM on-ground location is consistent with the Swift BAT position. The angle from the Fermi LAT boresight is 89 degrees. The GBM light curve consists of main emission episode with a duration (T90) of about 69 s (50-300 keV). The time-averaged spectrum from T0+0.000 to T0+69.120 s is best fit by a power law function. The power law index is -2.19 +/- 0.03. The event fluence (10-1000 keV) in this time interval is (6.18 +/- 0.29)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0+6.2 s in the 10-1000 keV band is 3.6 +/- 0.3 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog: https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html For Fermi GBM data and info, please visit the official Fermi GBM Support Page: View this GCN Circular online at https://gcn.nasa.gov/circulars/40422. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38452] IceCube-250506A: No Transient Candidates from the Zwicky Transient Facility
by GCN Circulars 10 May '25

10 May '25

TITLE: GCN CIRCULAR NUMBER: 40421 SUBJECT: IceCube-250506A: No Transient Candidates from the Zwicky Transient Facility DATE: 25/05/10 16:32:23 GMT FROM: Robert David Stein at JSI <rdstein(a)umd.edu> Akshay Eranhalodi (DESY), Robert Stein (JSI), Jannis Necker (DESY), Anna Franckowiak (Ruhr University Bochum) and Jesper Sollerman (Stockholm) report: On behalf of the Zwicky Transient Facility (ZTF) and Global Relay of Observatories Watching Transients Happen (GROWTH) collaborations: As part of the ZTF neutrino follow up program (Stein et al. 2023), we observed the localization region of the neutrino event IceCube-250506A (Zegarelli et. al, GCN 40369) with the Palomar 48-inch telescope, equipped with the 47 square degree ZTF camera (Bellm et al. 2019, Graham et al. 2019). We started observations in the g- and r-band beginning at 2025-05-08 04:24 UTC, approximately 38.2 hours after event time. Observations were delayed due to poor weather. We covered 78.5% (0.7 sq deg) of the reported localization region. This estimate accounts for chip gaps. Each exposure was 300s with a typical depth of 21.0 mag. The images were processed in real-time through the ZTF reduction and image subtraction pipelines at IPAC to search for potential counterparts (Masci et al. 2019). AMPEL (Nordin et al. 2019, Stein et al. 2021) was used to search the alerts database for candidates. We reject stellar sources (Tachibana and Miller 2018) and moving objects, and apply machine learning algorithms (Mahabal et al. 2019). We are left with the following high-significance candidate, lying within the 90.0% localization of the skymap. +--------------------------------------------------------------------------------+ | ZTF Name | IAU Name | RA (deg) | DEC (deg) | Filter | Mag | MagErr | +--------------------------------------------------------------------------------+ | ZTF23aabbszx | AT2023fyh | 116.1542766 | +35.3663416 | r | 19.29 | 0.17 | +--------------------------------------------------------------------------------+ ZTF23aabbszx is a nuclear source, and was first detected on 2023-01-25. It has a spectrum in DESI, with a redshift of z=0.3860 and clear AGN signatures. It similarly has AGN-like WISE colours of W1-W2=0.76. Based on this, we conclude that ZTF23aabbszx is an AGN. The source has been undergoing a long period of outburst, beginnning more than 800 days ago, with at least two distinct flares. The most recent flare began 300 days ago, and the source has been fading for the past 50 days. There is no particular activity in the past 6 months which suggest a connection to the high-energy neutrino. Observations of this field will continue as part of our standard ToO cadence for high-energy neutrinos (Stein et al. 2023). Based on observations obtained with the Samuel Oschin Telescope 48-inch and the 60-inch Telescope at the Palomar Observatory as part of the Zwicky Transient Facility project. ZTF is supported by the National Science Foundation under Award #2407588 and a partnership including Caltech, USA; Caltech/IPAC, USA; University of Maryland, USA; University of California, Berkeley, USA; University of Wisconsin at Milwaukee, USA; Cornell University, USA; Drexel University, USA; University of North Carolina at Chapel Hill, USA; Institute of Science and Technology, Austria; National Central University, Taiwan; Operations are conducted by Caltech's Optical Observatory (COO), Caltech/IPAC, and the University of Washington at Seattle, USA. GROWTH acknowledges generous support of the NSF under PIRE Grant No 1545949. Alert distribution service provided by DIRAC@UW (Patterson et al. 2019). Alert database searches are done by AMPEL (Nordin et al. 2019). Alert filtering is performed with the nuztf (Stein et al. 2021, https://github.com/desy-multimessenger/nuztf ). View this GCN Circular online at https://gcn.nasa.gov/circulars/40421. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38451] GRB 250510A: follow-up observation with EP-FXT
by GCN Circulars 10 May '25

10 May '25

TITLE: GCN CIRCULAR NUMBER: 40420 SUBJECT: GRB 250510A: follow-up observation with EP-FXT DATE: 25/05/10 15:12:36 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> A. Li, B. B. Zhang (BNU), Q. C. Liu (THU), Z. X. Ling (NAOC, CAS) on behalf of the Einstein Probe (EP) team: Following the possible detection of the GRB 250510A (Cheng et al., GCN 40415) and its multi-wavelength follow-up observations (Antier et al., GCN 40417), we performed an observation with the Follow-up X-ray Telescope (FXT) on board the Einstein Probe mission. The observations began at 2025-05-10T07:54:01 (UTC), about 3.3 hours after the SVOM-ECLAIRs detection. The exposure time is 4035 seconds. Preliminary analysis shows there are three source was detected in this epoch within the ECLAIRs error circle: ------------------------------------------------------------------------------------------------------ | Source Name | RA | DEC | Flux(erg/s/cm2) | Flux_err | ------------------------------------------------------------------------------------------------------ |EPF_J185647.0+182414| 284.1957 | 18.4041 | 9.91e-14 | 3.41e-14 | ------------------------------------------------------------------------------------------------------ |EPF_J185624.3+182129| 284.1012 | 18.3581 | 1.07e-13 | 2.59e-14 | ------------------------------------------------------------------------------------------------------ |EPF_J185624.8+181937| 284.1033 | 18.3269 | 1.35e-13 | 2.92e-14 | ------------------------------------------------------------------------------------------------------ EP-FXT will continue monitoring the source. More 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/40420. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38450] GRB 250510B: Swift/BAT-GUANO localization skymap of a burst
by GCN Circulars 10 May '25

10 May '25

TITLE: GCN CIRCULAR NUMBER: 40419 SUBJECT: GRB 250510B: Swift/BAT-GUANO localization skymap of a burst DATE: 25/05/10 13:48:28 GMT FROM: Samuele Ronchini at PSU <sjs8171(a)psu.edu> Samuele Ronchini (PSU), James DeLaunay (PSU), Aaron Tohuvavohu (Caltech), Gayathri Raman (PSU), Jamie A. Kennea (PSU), Tyler Parsotan (NASA GSFC) report: Swift/BAT did not localize GRB 250510B onboard (T0: 2025-05-10T06:41:54.06 UTC, Fermi GCN 40418) 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 11.67 in a 8.192 s analysis time bin, starting at T0 - 2.051 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 9,213 deg2 and the 50% credible area is 2,424 deg2. The integrated probability inside the coded field of view is 4%. The NITRATES skymap is consistent with the Fermi localization (GCN 40418). The combined Fermi/GBM+NITRATES 90% credible area is 550 deg2 and the 50% credible area is 116 deg2. A plot of the probability skymap can be viewed here: [skymap_plot](https://guano.swift.psu.edu/trigger_report?id=768552149/#:~:te… The probability skymap and joint skymap files can be downloaded from the links here [skymap_fits_file](https://guano.swift.psu.edu/files/768552149/0_n_PROBMAP) [joint_skymap_fits_file](https://guano.swift.psu.edu/files/768552149/0_n_JOI… 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=768552149 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/40419. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38449] GRB 250510B: Fermi GBM Final Localization
by GCN Circulars 10 May '25

10 May '25

TITLE: GCN CIRCULAR NUMBER: 40418 SUBJECT: GRB 250510B: Fermi GBM Final Localization DATE: 25/05/10 09:49:01 GMT FROM: A. Holzmann Airasca at University of Trento and INFN Bari <a.holzmannairasca(a)unitn.it> The Fermi GBM team reports the detection of a likely LONG GRB "At 06:41:54.06 UT on 10 May 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250510B (trigger 768552119/250510279). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 128.93, Dec = -24.76 (J2000 degrees, equivalent to J2000 08h 35m, -24d 45'), with a statistical uncertainty of 2.39 degrees. The angle from the Fermi LAT boresight is 103 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250510279/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250510279/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250510279/…" View this GCN Circular online at https://gcn.nasa.gov/circulars/40418. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38448] GRB 250510A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
by GCN Circulars 10 May '25

10 May '25

TITLE: GCN CIRCULAR NUMBER: 40417 SUBJECT: GRB 250510A: SVOM/COLIBRÍ (FM-GFT) optical upper limit DATE: 25/05/10 09:43:41 GMT FROM: Sarah Antier at OCA <sarah.antier(a)oca.eu> Sarah Antier (OCA), Noémie Globus (UNAM), Benjamin Schneider (LAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Fredd Alvarez (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (AUS), Rosa L. Becerra (U Roma), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Antonio de Ugarte Postigo (LAM), Y.H. Cheng (SWIFAR,YNU) and B.-T. Wang (YNAO, CAS): We imaged the field of the SVOM GRB 250510A (Cheng et al., GCN Circ. 40415) using the DDRAGO wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope. We observed from 2025-05-10 06:02:26 to 06:20:28 UTC (from 1.4 to 1.7 hours after the trigger) and obtained 16 minutes of exposure in the i filter under regular weather conditions. 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 catalog, is in the AB system, and is not corrected for Galactic extinction. In the stacked image, we do not detect any new source at the ECLAIRs source position (Cheng et al., GCN Circ. 40415) down to the following 5-sigma limit: i > 20.84 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/40417. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38447] GRB 250509A: Swift-XRT refined Analysis
by GCN Circulars 10 May '25

10 May '25

TITLE: GCN CIRCULAR NUMBER: 40416 SUBJECT: GRB 250509A: Swift-XRT refined Analysis DATE: 25/05/10 09:02:56 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), M.G. Bernardini (INAF-OAB), E. Ambrosi (INAF-IASFPA) , M. Capalbi (INAF-IASFPA), S. Dichiara (PSU), J.A. Kennea (PSU), D.N. Burrows (PSU) and P.A. Evans report on behalf of the Swift-XRT team: We have analysed 6.8 ks of XRT data for GRB 250509A, from 63 s to 28.3 ks after the trigger. The data comprise 156 s in Windowed Timing (WT) mode (the first 6 s were taken while Swift was slewing) with the remainder in Photon Counting (PC) mode. The light curve can be modelled with a series of power-law decays. The initial decay index is alpha=3.20 (+/-0.09). At T+349 s the decay flattens to an alpha of -1.1 (+0.7, -0.4) before breaking again at T+1377 s to a final decay with index alpha=1.44 (+0.10, -0.09). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 2.02 (+0.11, -0.10). The best-fitting absorption column is 6.6 (+/-0.7) x 10^21 cm^-2, in excess of the Galactic value of 2.0 x 10^20 cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 2.13 (+/-0.15) and a best-fitting absorption column of 6.0 (+1.0, -0.9) x 10^21 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 4.1 x 10^-11 (7.5 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 6.0 (+1.0, -0.9) x 10^21 cm^-2 Galactic foreground: 2.0 x 10^20 cm^-2 Excess significance: 10.7 sigma Photon index: 2.13 (+/-0.15) If the light curve continues to decay with a power-law decay index of 1.44, the count rate at T+24 hours will be 9.5 x 10^-3 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 3.9 x 10^-13 (7.1 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/01311764. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/40416. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38446] GRB 250510A: SVOM possible detection of a burst
by GCN Circulars 10 May '25

10 May '25

TITLE: GCN CIRCULAR NUMBER: 40415 SUBJECT: GRB 250510A: SVOM possible detection of a burst DATE: 25/05/10 05:51:17 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Y.H. Cheng (SWIFAR,YNU), B.-T. Wang (YNAO, CAS), W. J. Xie, D. H. ZHAO (NAO, CAS) on behalf of the SVOM mission team. SVOM/ECLAIRs triggered and located GRB 250510A (SVOM burst-id sb25051002) at 2025-05-10T04:38:52.34 UTC (Tb). The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network. The burst was only detected by the Count-Rate Trigger (CRT), which produced a sequence of 1 alert. CRT provided the alert with the best signal-to-noise-ratio (SNR) of 7.16 in the [20-120] keV energy band over a time window of 10.20 seconds starting at Tb. The localization of the best alert is R.A., Dec. 284.17, 18.37 degrees: R.A. (J2000) = 18h56m41.69s Dec. (J2000) = 18d22m20.68s with a 90% confidence level (C.L.) radius of 10.94 arcmin (including systematic error of 2 arcmin added in quadrature). Due to the trigger SNR less than the slew threshold, no immediate slew was performed on this burst. 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. The Burst Advocate (BA) on shift for this burst is Yehao Cheng: yhcheng(a)mail.ynu.edu.cn. Please contact the BA by email if you require additional information regarding the SVOM follow-up of this burst. View this GCN Circular online at https://gcn.nasa.gov/circulars/40415. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38445] GRB 250507A: J-band observations with WINTER
by GCN Circulars 10 May '25

10 May '25

TITLE: GCN CIRCULAR NUMBER: 40414 SUBJECT: GRB 250507A: J-band observations with WINTER DATE: 25/05/10 03:13:29 GMT FROM: Geoffrey Mo at MIT <gmo(a)mit.edu> Geoffrey Mo (MIT), Tomas Ahumada (Caltech), Benjamin Schneider (LAM), Viraj Karambelkar (Caltech), Robert Stein (UMD), Danielle Frostig (CfA), Nathan Lourie (MIT), Robert Simcoe (MIT), and Mansi Kasliwal (Caltech) report: We observed the field of GRB 250507A (Wang et al., GCN 40374) in the near-infrared J-band with the Palomar 1-m telescope, equipped with the 1-square degree WINTER camera (Lourie et al. 2020, Frostig et al. 2024). Observations were triggered automatically and began at 2025-05-09T05:54:11 UTC (1.97 days after the GRB), consisting of 15 x 120 s exposures. The images were processed using the WINTER data reduction pipeline implemented with mirar (https://github.com/winter-telescope/mirar, https://doi.org/10.5281/zenodo.13352565). We do not detect any uncataloged sources in the SVOM/MXT (Wang et al., GCN 40374; Maggi et al., GCN 40381), EP-FXT (Zhang et al., GCN 40385), or Swift-XRT (Osborne et al., GCN 40389) localizations after visual comparison to archival PanSTARRS-1 (Chambers et al. 2016) y-band imaging. This is consistent with observations by Ducoin et al., GCN 40376; Xin et al., GCN 40379; Brivio et al., GCN 40380; and Zheng et al., GCN 40400. We obtain the following 5-sigma upper limit: J ~ 19.5 mag (AB). WINTER (Wide-field INfrared Transient ExploreR) is a partnership between MIT and Caltech, housed at Palomar Observatory, and funded by NSF MRI, NSF AAG, the David and Lucile Packard Foundation, and the MIT Kavli Institute for Astrophysics and Space Research. View this GCN Circular online at https://gcn.nasa.gov/circulars/40414. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38444] GRB 250507A: J-band observations with WINTER
by GCN Circulars 10 May '25

10 May '25

TITLE: GCN CIRCULAR NUMBER: 40413 SUBJECT: GRB 250507A: J-band observations with WINTER DATE: 25/05/10 03:12:44 GMT FROM: Geoffrey Mo at MIT <gmo(a)mit.edu> Geoffrey Mo (MIT), Tomas Ahumada (Caltech), Benjamin Schneider (LAM), Viraj Karambelkar (Caltech), Robert Stein (UMD), Danielle Frostig (CfA), Nathan Lourie (MIT), Robert Simcoe (MIT), and Mansi Kasliwal (Caltech) report: We observed the field of GRB 250507A (Wang et al., GCN 40374) in the near-infrared J-band with the Palomar 1-m telescope, equipped with the 1-square degree WINTER camera (Lourie et al. 2020, Frostig et al. 2024). Observations were triggered automatically and began at 2025-05-09T05:54:11 UTC (1.97 days after the GRB), consisting of 15 x 120 s exposures. The images were processed using the WINTER data reduction pipeline implemented with mirar (https://github.com/winter-telescope/mirar, https://doi.org/10.5281/zenodo.13352565). We do not detect any uncataloged sources in the SVOM/MXT (Wang et al., GCN 40374; Maggi et al., GCN 40381), EP-FXT (Zhang et al., GCN 40385), or Swift-XRT (Osborne et al., GCN 40389) localizations after visual comparison to archival PanSTARRS-1 (Chambers et al. 2016) y-band imaging. This is consistent with observations by Ducoin et al., GCN 40376; Xin et al., GCN 40379; Brivio et al., GCN 40380; and Zheng et al., GCN 40400. We obtain the following 5-sigma upper limit: J ~ 19.5 mag (AB). WINTER (Wide-field INfrared Transient ExploreR) is a partnership between MIT and Caltech, housed at Palomar Observatory, and funded by NSF MRI, NSF AAG, the David and Lucile Packard Foundation, and the MIT Kavli Institute for Astrophysics and Space Research. View this GCN Circular online at https://gcn.nasa.gov/circulars/40413. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38443] GRB 250507A: J-band observations with WINTER
by GCN Circulars 10 May '25

10 May '25

TITLE: GCN CIRCULAR NUMBER: 40413 SUBJECT: GRB 250507A: J-band observations with WINTER DATE: 25/05/10 03:12:44 GMT FROM: Geoffrey Mo at MIT <gmo(a)mit.edu> Geoffrey Mo (MIT), Tomas Ahumada (Caltech), Benjamin Schneider (LAM), Viraj Karambelkar (Caltech), Robert Stein (UMD), Danielle Frostig (CfA), Nathan Lourie (MIT), Robert Simcoe (MIT), and Mansi Kasliwal (Caltech) report: We observed the field of GRB 250507A (Wang et al., GCN 40374) in the near-infrared J-band with the Palomar 1-m telescope, equipped with the 1-square degree WINTER camera (Lourie et al. 2020, Frostig et al. 2024). Observations were triggered automatically and began at 2025-05-09T05:54:11 UTC (1.97 days after the GRB), consisting of 15 x 120 s exposures. The images were processed using the WINTER data reduction pipeline implemented with mirar (https://github.com/winter-telescope/mirar, https://doi.org/10.5281/zenodo.13352565). We do not detect any uncataloged sources in the SVOM/MXT (Wang et al., GCN 40374; Maggi et al., GCN 40381), EP-FXT (Zhang et al., GCN 40385), or Swift-XRT (Osborne et al., GCN 40389) localizations after visual comparison to archival PanSTARRS-1 (Chambers et al. 2016) y-band imaging. This is consistent with observations by Ducoin et al., GCN 40376; Xin et al., GCN 40379; Brivio et al., GCN 40380; and Zheng et al., GCN 40400. We obtain the following 5-sigma upper limit: J ~ 19.5 mag (AB). WINTER (Wide-field INfrared Transient ExploreR) is a partnership between MIT and Caltech, housed at Palomar Observatory, and funded by NSF MRI, NSF AAG, the David and Lucile Packard Foundation, and the MIT Kavli Institute for Astrophysics and Space Research. View this GCN Circular online at https://gcn.nasa.gov/circulars/40413. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38442] EP250508a: SVOM/VT optical candidate fading
by GCN Circulars 10 May '25

10 May '25

TITLE: GCN CIRCULAR NUMBER: 40412 SUBJECT: EP250508a: SVOM/VT optical candidate fading DATE: 25/05/10 01:53:50 GMT FROM: Huali Li at at NAOC, SVOM <lhl(a)nao.cas.cn> H. L. Li, L. P. Xin, Y. L. Qiu, C. Wu, Z. H. Yao, Y. N. Ma, 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, T. Zhao, R. D. Liang, H. Q. Cheng, W. D. Zhang (NAOC, CAS), Y. D. Hu (GXU), L. Zhang (IHEP), X. L. Chen(YNU) report on behalf of the SVOM and EP Teams: SVOM/VT made a second ToO observation for EP250508a (Liang et al., GCN 40390，Zhao et al., GCN 40399) at about 29.44 hour after trigger. The observation was performed in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. The brightness of the candidate reported by Xin et al. (GCN 40402) was VT_R=23.9+/-0.3 mag and VT_B>24.0 with the exposure time of 52*100 seconds. Our photometry was derived in AB magnitude and not corrected for Galactic extinction. Considering the fading behavior of the candidate, we suggest that it is the optical counterpart of the transient. The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC),CAS. View this GCN Circular online at https://gcn.nasa.gov/circulars/40412. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38441] GRB 250509A: Enhanced Swift-XRT position
by GCN Circulars 10 May '25

10 May '25

TITLE: GCN CIRCULAR NUMBER: 40411 SUBJECT: GRB 250509A: Enhanced Swift-XRT position DATE: 25/05/10 01:51:55 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> A.P. Beardmore, P.A. Evans, M.R. Goad and J.P. Osborne (U. Leicester) report on behalf of the Swift-XRT team. Using 877 s of XRT Photon Counting mode data and 2 UVOT images for GRB 250509A, we find an astrometrically corrected X-ray position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 46.44965, -38.84201 which is equivalent to: RA (J2000): 03h 05m 47.92s Dec (J2000): -38d 50' 31.2" with an uncertainty of 2.3 arcsec (radius, 90% confidence). This position may be improved as more data are received. The latest position can be viewed at http://www.swift.ac.uk/xrt_positions. Position enhancement is described by Goad et al. (2007, A&A, 476, 1401) and Evans et al. (2009, MNRAS, 397, 1177). This circular was automatically generated, and is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/40411. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38440] GRB 250509A: Prompt enhanced Swift-XRT position
by GCN Circulars 09 May '25

09 May '25

TITLE: GCN CIRCULAR NUMBER: 40410 SUBJECT: GRB 250509A: Prompt enhanced Swift-XRT position DATE: 25/05/09 23:32:52 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-XRT team: Using 426 s of promptly downlinked XRT event data for GRB 250509A, we find an enhanced XRT position of the afterglow: RA, Dec: 46.44960, -38.84128 which is equivalent to: RA (J2000) = 03 05 47.90 Dec (J2000) = -38 50 28.6 with an uncertainty of 1.9 arcseconds (radius, 90% confidence). Analysis of the promptly available data is online at http://www.swift.ac.uk/sper/1311764. Position enhancement is described by Goad et al. (2007, A&A, 476, 1401) and Evans et al. (2009, MNRAS, 397, 1177). This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/40410. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38439] Fermi GRB 250509A: Global MASTER-Net observations report
by GCN Circulars 09 May '25

09 May '25

TITLE: GCN CIRCULAR NUMBER: 40409 SUBJECT: Fermi GRB 250509A: Global MASTER-Net observations report DATE: 25/05/09 23:31:05 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 250509A ( Fermi GBM team, GCN 40406) errorbox 7 sec after notice time and 64 sec after trigger time at 2025-05-09 22:34:33 UT, with upper limit up to 18.4 mag. Observations started at twilight. The observations began at zenith distance = 70 deg. The sun altitude is -9.7 deg. The galactic latitude b = -60 deg., longitude l = 237 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2866536 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 70 | 2025-05-09 22:34:33 | MASTER-OAFA | (03h 18m 00.28s , -38d 23m 19.1s) | C | 10 | 14.1 | 104 | 2025-05-09 22:35:03 | MASTER-OAFA | (03h 18m 00.24s , -38d 23m 19.1s) | C | 20 | 14.5 | 138 | 2025-05-09 22:35:42 | MASTER-OAFA | (03h 18m 00.14s , -38d 23m 18.9s) | C | 10 | 14.4 | 174 | 2025-05-09 22:36:18 | MASTER-OAFA | (03h 18m 00.11s , -38d 23m 18.5s) | C | 10 | 14.4 | 215 | 2025-05-09 22:36:53 | MASTER-OAFA | (03h 18m 00.10s , -38d 23m 18.6s) | C | 20 | 14.7 | 265 | 2025-05-09 22:37:39 | MASTER-OAFA | (03h 18m 00.12s , -38d 23m 19.3s) | C | 30 | 14.8 | 865 | 2025-05-09 22:46:44 | MASTER-OAFA | (03h 18m 00.32s , -38d 23m 28.0s) | C | 140 | 14.8 | 1041 | 2025-05-09 22:49:30 | MASTER-OAFA | (03h 18m 00.52s , -38d 23m 31.2s) | C | 160 | 16.3 | 1227 | 2025-05-09 22:52:36 | MASTER-OAFA | (03h 18m 00.73s , -38d 23m 34.3s) | C | 160 | 16.5 | 1414 | 2025-05-09 22:55:42 | MASTER-OAFA | (03h 18m 01.03s , -38d 23m 38.0s) | C | 160 | 17.0 | 1424 | 2025-05-09 22:55:43 | MASTER-OAFA | (03h 06m 24.43s , -38d 43m 44.4s) | C | 180 | 18.2 | 1600 | 2025-05-09 22:58:49 | MASTER-OAFA | (03h 18m 01.35s , -38d 23m 42.3s) | C | 160 | 17.1 | 1610 | 2025-05-09 22:58:49 | MASTER-OAFA | (03h 06m 24.67s , -38d 43m 47.0s) | C | 180 | 18.4 | 1786 | 2025-05-09 23:01:55 | MASTER-OAFA | (03h 18m 01.74s , -38d 23m 46.7s) | C | 160 | 17.1 | 1796 | 2025-05-09 23:01:55 | MASTER-OAFA | (03h 06m 24.96s , -38d 43m 50.0s) | C | 180 | 18.3 | 1972 | 2025-05-09 23:05:01 | MASTER-OAFA | (03h 18m 02.05s , -38d 23m 50.9s) | C | 160 | 17.1 | 1983 | 2025-05-09 23:05:02 | MASTER-OAFA | (03h 06m 25.27s , -38d 43m 53.2s) | C | 180 | 18.2 | 2159 | 2025-05-09 23:08:08 | MASTER-OAFA | (03h 18m 02.30s , -38d 23m 55.2s) | C | 160 | 17.1 | 2169 | 2025-05-09 23:08:08 | MASTER-OAFA | (03h 06m 25.58s , -38d 43m 56.5s) | C | 180 | 18.1 | 2356 | 2025-05-09 23:11:14 | MASTER-OAFA | (03h 06m 25.97s , -38d 44m 00.1s) | C | 180 | 18.0 | 2531 | 2025-05-09 23:14:20 | MASTER-OAFA | (03h 18m 02.98s , -38d 24m 03.8s) | C | 160 | 17.1 | 2542 | 2025-05-09 23:14:20 | MASTER-OAFA | (03h 06m 26.35s , -38d 44m 03.6s) | C | 180 | 18.0 | 2718 | 2025-05-09 23:17:26 | MASTER-OAFA | (03h 18m 03.37s , -38d 24m 09.0s) | C | 160 | 17.2 | 2728 | 2025-05-09 23:17:27 | MASTER-OAFA | (03h 06m 26.66s , -38d 44m 06.7s) | C | 180 | 18.0 | 2904 | 2025-05-09 23:20:33 | MASTER-OAFA | (03h 18m 03.73s , -38d 24m 14.1s) | C | 160 | 17.1 | 2914 | 2025-05-09 23:20:33 | MASTER-OAFA | (03h 06m 26.94s , -38d 44m 08.8s) | C | 180 | 17.6 | 3090 | 2025-05-09 23:23:39 | MASTER-OAFA | (03h 18m 04.07s , -38d 24m 19.9s) | C | 160 | 16.9 | 3100 | 2025-05-09 23:23:39 | MASTER-OAFA | (03h 06m 27.22s , -38d 44m 12.4s) | C | 180 | 17.4 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. View this GCN Circular online at https://gcn.nasa.gov/circulars/40409. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38438] Swift GRB 250509A: Global MASTER-Net observations report
by GCN Circulars 09 May '25

09 May '25

TITLE: GCN CIRCULAR NUMBER: 40408 SUBJECT: Swift GRB 250509A: Global MASTER-Net observations report DATE: 25/05/09 23:06:47 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 Swift GRB 250509A ( M. H. Siegel et al., GCN 40407) errorbox 1296 sec after notice time and 1332 sec after trigger time at 2025-05-09 22:55:43 UT, with upper limit up to 18.4 mag. Observations started at twilight. The observations began at zenith distance = 76 deg. The sun altitude is -14.1 deg. The galactic latitude b = -59 deg., longitude l = 244 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2866479 We obtain a following upper limits. Tmid-T0 | Site |Filt.| Expt. | Limit| Comment _________|_____________________|_____|_______|______|________ 1423 | MASTER-OAFA | C | 180 | 18.2 | 1609 | MASTER-OAFA | C | 180 | 18.4 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. View this GCN Circular online at https://gcn.nasa.gov/circulars/40408. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38437] GRB 250509A: Swift detection of a burst
by GCN Circulars 09 May '25

09 May '25

TITLE: GCN CIRCULAR NUMBER: 40407 SUBJECT: GRB 250509A: Swift detection of a burst DATE: 25/05/09 22:49:14 GMT FROM: Mike Siegel at PSU/Swift MOC <siegel(a)swift.psu.edu> M. H. Siegel (PSU), S. Dichiara (PSU), R. Gupta (NASA GSFC) and B. Sbarufatti (INAF-OAB) report on behalf of the Neil Gehrels Swift Observatory Team: At 22:33:30 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 250509A (trigger=1311764). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 46.455, -38.853 which is RA(J2000) = 03h 05m 49s Dec(J2000) = -38d 51' 11" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a multi peak structure with a duration of about 60 sec. The peak count rate was ~2800 counts/sec (15-350 keV), at ~0 sec after the trigger. The XRT began observing the field at 22:34:41.7 UT, 71.1 seconds after the BAT trigger. Using promptly downlinked data we find a bright, uncatalogued X-ray source located at RA, Dec 46.45032, -38.84173 which is equivalent to: RA(J2000) = 03h 05m 48.08s Dec(J2000) = -38d 50' 30.2" with an uncertainty of 3.6 arcseconds (radius, 90% containment). This location is 42 arcseconds from the BAT onboard position, within the BAT error circle. This position may be improved as more data are received; the latest position is available at https://www.swift.ac.uk/sper. A power-law fit to a spectrum formed from promptly downlinked event data gives a column density in excess of the Galactic value (2.03 x 10^20 cm^-2, Willingale et al. 2013), with an excess column of 9.2 (+3.98/-3.41) x 10^21 cm^-2 (90% confidence). The initial flux in the 2.5 s image was 7.21e-09 erg cm^-2 s^-1 (0.2-10 keV). UVOT took a finding chart exposure of nominal 150.000 seconds with the White filter starting 80 seconds after the BAT trigger. No credible afterglow candidate has been found in the initial data products. Data from the 2.7'x2.7' sub-image are not available at this time. The 8'x8' region for the list of sources generated on-board covers 100% of the XRT error circle. The list of sources is typically complete to about 18 mag. No correction has been made for the expected extinction corresponding to E(B-V) of 0.021. Burst Advocate for this burst is M. H. Siegel (siegel AT swift.psu.edu). 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/40407. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38436] GRB 250509A: Fermi GBM Final Real-time Localization
by GCN Circulars 09 May '25

09 May '25

TITLE: GCN CIRCULAR NUMBER: 40406 SUBJECT: GRB 250509A: Fermi GBM Final Real-time Localization DATE: 25/05/09 22:43:58 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 22:33:29 UT on 9 May 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250509A (trigger 768522814.285632 / 250509940). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 46.0, Dec = -35.3 (J2000 degrees, equivalent to J2000 03h 04m, -35d 17'), with a statistical uncertainty of 3.0 degrees. The angle from the Fermi LAT boresight is 89.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250509940/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250509940/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250509940/… View this GCN Circular online at https://gcn.nasa.gov/circulars/40406. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38435] GRB 250506A: NOT optical upper limits
by GCN Circulars 09 May '25

09 May '25

TITLE: GCN CIRCULAR NUMBER: 40405 SUBJECT: GRB 250506A: NOT optical upper limits DATE: 25/05/09 09:37:58 GMT FROM: Gregory Corcoran at University College Dublin <gregory.corcoran(a)ucdconnect.ie> Z. P. Zhu (NAOC), B. Schneider (LAM), A. Martin-Carrillo (UCD), G. Corcoran (UCD), D. B. Malesani (DAWN/NBI and Radboud), D. Xu (NAOC), T. T. Hansen, W. M. Ali, P. H. Chan, N. Hölinger, E. Lamprou, R. Lesley, H. Lundberg, J. Pajak, L. Peschieras, and N. Valsamidis (all Stockholm University), report on behalf of a larger collaboration. We observed the field of GRB 250506A detected by SVOM/ECLAIRs (Wang et al., GCN 40358) and Fermi/GBM (Sonawane et al., GCN 40362), using the ALFOSC camera mounted on the Nordic Optical Telescope (NOT) centered at the X-ray source detected by EP/FXT (Zhang et al. GCN 40365). We obtained exposures in the SDSS r (3x600 s) and z (4x300 s) bands starting at 23:44:29 UT on 2025-05-06 (21.35 hr after the SVOM/ECLAIRs trigger). No new optical source is detected at a position consistent with the Swift/XRT error region (the best currently available for this event; Burrows et al., GCN 40378) in the stacked images of either band down to the 5-sigma limiting AB magnitudes of r > 23.6 and z > 22.5, calibrated against nearby Pan-STARRS stars. View this GCN Circular online at https://gcn.nasa.gov/circulars/40405. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38434] EP250508a: Liverpool Telescope optical upper limits
by GCN Circulars 09 May '25

09 May '25

TITLE: GCN CIRCULAR NUMBER: 40404 SUBJECT: EP250508a: Liverpool Telescope optical upper limits DATE: 25/05/09 09:01:45 GMT FROM: Rob Eyles-Ferris at U of Leicester <raje1(a)leicester.ac.uk> R. A. J. Eyles-Ferris, P. T. O’Brien and R. L. C. Starling (U of Leicester) report: We observed the field of the X-ray transient EP250508a (Liang et al., GCN 40390; Zhao et al., GCN 40399; Liang et al., GCN 40403) with the 2m Liverpool Telescope using the IO:O instrument. We obtained 6x150s exposures in the SDSS r’ filter starting at 2025-05-08 21:07:19 UT and 6x150s exposures in the SDSS z’ filter starting at 2025-05-08 21:24:25 UT, approximately 15.1 hours after the X-ray detection. We performed image subtraction on the stacked images using reference images from Pan-STARRS and also compared the stacked and reference images manually. Consistent with Ugarte Postigo et al. (GCN 40391), Lipunov et al. (GCN 40393), Brivio et al. (GCN 40395) and Zheng et al. (GCN 40401), we identify no new sources within the error region of the EP/FXT source. At the position of the optical counterpart candidate identified by Xin et al. (GCN 40402), we derive 3-sigma upper limits of r’ > 21.5 and z’ > 21.5 with photometry calibrated to Pan-STARRS and not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/40404. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38433] EP250508a: Liverpool Telescope optical upper limits
by GCN Circulars 09 May '25

09 May '25

TITLE: GCN CIRCULAR NUMBER: 40404 SUBJECT: EP250508a: Liverpool Telescope optical upper limits DATE: 25/05/09 09:01:45 GMT FROM: Rob Eyles-Ferris at U of Leicester <raje1(a)leicester.ac.uk> R. A. J. Eyles-Ferris, P. T. O’Brien and R. L. C. Starling (U of Leicester) report: We observed the field of the X-ray transient EP250508a (Liang et al., GCN 40390; Zhao et al., GCN 40399; Liang et al., GCN 40403) with the 2m Liverpool Telescope using the IO:O instrument. We obtained 6x150s exposures in the SDSS r’ filter starting at 2025-05-08 21:07:19 UT and 6x150s exposures in the SDSS z’ filter starting at 2025-05-08 21:24:25 UT, approximately 15.1 hours after the X-ray detection. We performed image subtraction on the stacked images using reference images from Pan-STARRS and also compared the stacked and reference images manually. Consistent with Ugarte Postigo et al. (GCN 40391), Lipunov et al. (GCN 40393), Brivio et al. (GCN 40395) and Zheng et al. (GCN 40401), we identify no new sources within the error region of the EP/FXT source. At the position of the optical counterpart candidate identified by Xin et al. (GCN 40402), we derive 3-sigma upper limits of r’ > 21.5 and z’ > 21.5 with photometry calibrated to Pan-STARRS and not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/40404. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38432] EP250508a: follow-up observation with EP-FXT
by GCN Circulars 09 May '25

09 May '25

TITLE: GCN CIRCULAR NUMBER: 40403 SUBJECT: EP250508a: follow-up observation with EP-FXT DATE: 25/05/09 08:07:31 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> R. D. Liang, T. Zhao, H. Q. Cheng, W. D. Zhang (NAOC, CAS) on behalf of the Einstein Probe (EP) team: Following the detection of the fast X-ray transient EP250508a (Liang et al., GCN 40390, Zhao et al. GCN 40399) and its multi-wavelength follow-up observations (Postigo et al., GCN 40391; Lipunov et al., GCN 40393; Brivio et al., GCN 40395; Zheng GCN 40401; Xin et al. GCN 40402), we performed an observation with the Follow-up X-ray Telescope (FXT) on board the Einstein Probe mission. The observations began at 2025-05-08 13:41:03 (UTC), about 7.6 hours after the EP-WXT detection. The exposure time is 7250 seconds. Preliminary analysis shows that the source was detected in this epoch. The spectrum in the 0.5-10 keV band can be fitted with an absorbed power-law model with NH fixed at the Galactic value of 3.56e20 cm^-2 and a photon index of 2.22(-0.47, +0.47). The unabsorbed 0.5-10 keV flux is 4.53(-1.88, +1.88)e-14 erg/s/cm^2 (90% C.L.), about five times lower than that detected in the autonomous FXT follow-up observation (Zhao et al. GCN 40399), demonstrating a rapid decay trend in the source's X-ray emission. EP-FXT will continue monitoring the source. More follow-up observations are encouraged. The contact TA of EP250508a is R. D. Liang. Please contact him via email liangrd(a)bao.ac.cn if needed. 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/40403. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38431] EP250508a: SVOM/VT optical candidate
by GCN Circulars 09 May '25

09 May '25

TITLE: GCN CIRCULAR NUMBER: 40402 SUBJECT: EP250508a: SVOM/VT optical candidate DATE: 25/05/09 05:40:30 GMT FROM: Liping Xin at NAOC, SVOM <xlp(a)nao.cas.cn> L. P. Xin, Y. L. Qiu, H. L. Li, C. Wu, Z. H. Yao, Y. N. Ma, 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, T. Zhao, R. D. Liang, H. Q. Cheng, W. D. Zhang (NAOC, CAS), Y. D. Hu (GXU), L. Zhang (IHEP), X. L. Chen(YNU) report on behalf of the SVOM and EP Teams: SVOM/VT observed the X-ray transient EP250508a (Liang et al., GCN 40390，Zhao et al., GCN 40399) in ToO mode in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. The observation started at 2025-05-08T11:38:19 UT, about 5.6 hours after the trigger. An uncatalogued faint candidate is detected in both channels within FXT error circle, compared to Legacy Survey, with the coordinate: RA= 11:53:01.05 (178.25438 deg) DEC=-19:55:24.2 (-19.92339 deg) Error = 0.5 arcseconds J2000 The brightness of the candidate is derived as below : Mid-time band mag(AB) exposure 6.74 hour VT_R 23.0+/-0.2 71*70 sec 6.75 hour VT_B 23.6+/-0.3 71*70 sec Our photometry was estimated in AB magnitude and not corrected for Galatic extinction. Give the faintness of the candidate, we cannot determine whether it is fading. More follow-ups are encouraged to confirm the nature of the transient. The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC),CAS. View this GCN Circular online at https://gcn.nasa.gov/circulars/40402. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38430] EP250508a: KAIT optical upper limit
by GCN Circulars 08 May '25

08 May '25

TITLE: GCN CIRCULAR NUMBER: 40401 SUBJECT: EP250508a: KAIT optical upper limit DATE: 25/05/08 18:38:55 GMT FROM: Weikang Zheng at UC Berkeley <weikang(a)berkeley.edu> WeiKang Zheng (UCB), Xuhui Han (NAOC), Pinpin Zhang (NAOC) 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 EP250508a (Liang et al., GCN 40390) starting at 06:17, May 08 UT, about 14 minutes after the burst. A set of clear (roughly R) filter images were obtained. Preliminary analysis do not reveal any new optical counterpart candidate within the X-ray afterglow error circles (Liang et al., GCN 40390; Zhao et al., GCN 40399). Due to the bright moonlight, our image quality are degraded and we estimate the limiting magnitude of our single image to be ~17.0 mag, shallower than the upper limit reported by other groups (Ugarte Postigo et al., GCN 40391; Lipunov et al., GCN 40393; Brivio et al., GCN 40395). View this GCN Circular online at https://gcn.nasa.gov/circulars/40401. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38429] GRB 250507A: KAIT optical upper limit
by GCN Circulars 08 May '25

08 May '25

TITLE: GCN CIRCULAR NUMBER: 40400 SUBJECT: GRB 250507A: KAIT optical upper limit DATE: 25/05/08 18:37:31 GMT FROM: Weikang Zheng at UC Berkeley <weikang(a)berkeley.edu> WeiKang Zheng (UCB), Xuhui Han (NAOC), Pinpin Zhang (NAOC) 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 SVOM GRB 250507A (Wang et al., GCN 40374) starting at 06:37:30, May 07 UT, 165 seconds after the burst. Observations were performed in 3 x 3 tiling mode, and a set of clear (roughly R) filter images were obtained. Preliminary analysis do not reveal any new optical counterpart candidate within the X-ray afterglow error circles (Maggi et al., GCN 40381; Zhang et al., GCN 40385; Osborne et al., GCN 40389), neither in single image, nor in the co-add images. We estimate the limiting magnitude of our coadd image to be ~20.0 mag at a mid-time of 15.0 minutes after the burst, consistent with the upper limit reported by other groups (Ducoin et al., GCN 40376; Xin et al., GCN 40379; Brivio et al., GCN 40380) View this GCN Circular online at https://gcn.nasa.gov/circulars/40400. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38428] EP250508a: refined analysis of the EP-WXT and EP-FXT observations
by GCN Circulars 08 May '25

08 May '25

TITLE: GCN CIRCULAR NUMBER: 40399 SUBJECT: EP250508a: refined analysis of the EP-WXT and EP-FXT observations DATE: 25/05/08 16:08:00 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> T.Zhao, R. D. Liang, H. Q. Cheng, W. D. Zhang (NAOC, CAS) on behalf of the Einstein Probe (EP) team: The X-ray transient EP250508a was detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Liang et al., GCN 40390), and followed up by several telescopes (Antonio et al, GCN 40391; Lipunov et al, GCN 40393; Brivio et al, GCN 40395). Refined analysis of the WXT data shows that the event started at T0=2025-05-08T06:02:28.850 (UTC) and lasted for about 60 s before the observation was interrupted by the autonomous follow-up observation. The peak flux is about 3.6 x 10^(-9) erg/s/cm^2. The averaged 0.5-4 keV spectrum can be fitted by an absorbed power law model with a Galactic hydrogen column density of 3.56 x 10^20 cm^-2 and a photon index of 0.91 (+/-0.54). The derived average unabsorbed 0.5-4 keV flux is 1.4 (-0.4/+0.5) x 10^(-9) erg/s/cm^2. The uncertainties are quoted at the 90% confidence level for the above parameters. The Follow-up X-ray Telescope (FXT) on board EP observed this source autonomously about 3 min after T0, starting at 2025-05-08T06:05:21 (UTC). Within the WXT error circle, on-ground analysis of the FXT data found an uncatalogued source at R.A. = 178.2555, DEC = -19.9244 (J2000) with an uncertainty of 10 arcsec (radius, 90% C.L. statistical and systematic). During the observation a decline in the source flux lasting for a few hundred seconds is observed from the beginning. The averaged 0.5-10 keV FXT spectrum can be fitted by an absorbed power law model with a Galactic hydrogen column density of 3.56 x 10^20 cm^-2 and a photon index of 2.30 (-0.45/+0.45). The derived average unabsorbed 0.5-10 keV flux is 2.0 (-0.5/+0.8) x 10^(-13) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. EP-FXT will continue monitoring this source. More follow-up observations are encouraged. The contact TA of EP250508a is R. D. Liang. Please contact him via email liangrd(a)bao.ac.cn if needed. 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/40399. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38427] GRB 250505B: SVOM/GRM observation of a short burst
by GCN Circulars 08 May '25

08 May '25

TITLE: GCN CIRCULAR NUMBER: 40398 SUBJECT: GRB 250505B: SVOM/GRM observation of a short burst DATE: 25/05/08 15:29:40 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, Laurent Bouchet (IRAP), Frédéric Piron (LUPM), Stéphane Schanne (CEA) report on behalf of the SVOM team: SVOM/GRM was triggered in-flight by a short burst GRB 250505A at 2025-05-05T02:10:34 UTC (T0). With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of a narrow spike followed by a tail with a T90 of 0.26 +0.13/-0.07 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb250505A.png The SVOM/GRM on-ground localization of this burst is (J2000): RA: 55.6 deg DEC: -39.0 deg Error: 4.6 deg (1sigma, statistical only) We caution that the calibration of SVOM/GRM is undergoing and this localization is subject to systematic errors. In addition, the position of this burst, as determined by GRM, is located at about 95 degrees from the SVOM optical axis. ECLAIRs was in operation during the burst but no significant signal is detected, which confirms that the burst occurred outside the ECLAIRs field of view. With this localization, the time-averaged spectrum from T0+0.02 to T0+0.15 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.10 +0.37/-0.35 and the cutoff energy, parameterized as Epeak, is 70 +/-10 keV. The event fluence (10-1000 keV) in this time interval is (5.9 +0.6/-0.5)E-07 erg/cm^2. The localization of GRB 250505A in the 'Amati' relation diagram is shown at: https://www.bursthub.cn//admin/static/grb250505A_amati.png We note that the Epeak of this burst is relatively soft in short GRBs, while the hardness and duration are both similar to a magnetar X-ray burst. 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/40398. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38426] GRB 250502A: Calapai Observatory, Massa S. Giorgio (Messina), optical observation.
by GCN Circulars 08 May '25

08 May '25

TITLE: GCN CIRCULAR NUMBER: 40397 SUBJECT: GRB 250502A: Calapai Observatory, Massa S. Giorgio (Messina), optical observation. DATE: 25/05/08 14:26:33 GMT FROM: Giovanni Calapai at Calapai Astronomical Observatory, Massa S. Giorgio, Messina, Italy <giovannicalapai(a)tiscali.it> Giovanni Calapai at Calapai Astronomical Observatory, Massa S. Giorgio, (Messina) Italy Member of: GRB/UAI Gamma Ray Burst Section of Unione Astrofili Italiani. Report: we observed the field of GRB 250502A detected by SVOM/ECLAIRs (Wang et al. GCN 40313) with the 11 inches Schmidt-Cassegrain (Celestron 11) telescope F/D=6,3. The observations were started at 2025-05-02 21:24 UT (approximately 12.62 hours after burst) stacking a set of unfiltered CCD image. The observations were carried out with clear skies and good visibility conditions. We detected a very faint object at the following position: RA (J2000.0) 13h 46m 05.62s Decl. (J2000.0) -10° 45' 32.3" Photometry was obtained using nearby PanSTARRS stars as follows: Observation Mid-Time T-T0 (hr) Exposure Filter Mag. Mag. err. 2025-05-02 23:44:41 UT 14.97 200x60s CR 20.70 +/-0.16 Magnitude was calibrated with the nearby PanSTARRS stars converted using Lupton (2005) equations. No correction for galactic dust extinction was applied. Our observations are consistent with other already reported Rakotondrainibe et al. GCN 40315; An et al. GCN 40319; Li et al. GCN 40320; Ghosh et al. GCN 40322; de Ugarte Postigo et al. GCN 40328; Pérez-Fournon et al. GCN 40330; Odeh et al. GCN 40331; Bochenek & Perley GCN 40333; Corcoran et al. GCN 40334; Leonini et al. GCN 40337; Zheng et al. GCN 40338; Pankov et al. GCN 40339; Brivio et al. GCN 40349; Quadri et al. GCN 40370. The message may be cited. View this GCN Circular online at https://gcn.nasa.gov/circulars/40397. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38425] GRB 250506A: GECAM detection
by GCN Circulars 08 May '25

08 May '25

TITLE: GCN CIRCULAR NUMBER: 40396 SUBJECT: GRB 250506A: GECAM detection DATE: 25/05/08 14:13:56 GMT FROM: Chenwei Wang at IHEP <cwwang(a)ihep.ac.cn> Chen-Wei Wang, Shao-Lin Xiong (IHEP) report on behalf of GECAM team: GECAM-B was triggered in-flight by GRB 250506A at 2025-05-06T02:23:22.850 UTC (denoted as T0), which was also detected by Fermi/GBM (Fermi GBM team, GCN #40355) and SVOM (Wang et al., GCN #40358). According to the GECAM-B light curves in about 40-6000 keV, this burst mainly consists of multiple pulses with a duration (T90) of 34.6 +0.8/-1.9 s. The GECAM-B light curve can be found here: https://www.bursthub.cn//admin/static/gecamgrb250506A.png With the localization of RA, Dec = 219.28269, +28.87835, as determined by Swift/XRT (D.N. Burrows et al., GCN #40394), the time-averaged spectrum from T0-10s to T0+60 s is best fitted by a powerlaw with an alpha of -2.02 +/- 0.11. The event fluence (10-1000 keV) in this time interval is (2.60 +/- 0.14)E-05 erg/cm^2. 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/40396. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 38424] EP250508a: REM optical/NIR observations
by GCN Circulars 08 May '25

08 May '25

TITLE: GCN CIRCULAR NUMBER: 40395 SUBJECT: EP250508a: REM optical/NIR observations DATE: 25/05/08 10:22:35 GMT FROM: Riccardo Brivio at INAF-OAB <riccardo.brivio(a)inaf.it> R. Brivio, M. Ferro, P. D'Avanzo, S. Covino, D. Fugazza (INAF-OAB) report on behalf of the REM team: We observed the field of GRB EP250508a detected by EP/WXT (Liang et al., GCN 40390) with the REM 60 cm robotic telescope located at the ESO observatory of La Silla (Chile). The observations were carried in the g, r, i, z, J, H, and K bands, started on 2025 May 08 at 06:12:51 UT (i.e. about 9 minutes after the burst), and lasted for about 2 hours. From preliminary inspection, we do not detect any possible counterpart inside the EP/FXT error circle down to the following 3sigma limits: r > 19.2 (AB; calibrated against the Pan-STARRS catalogue), at a mid-time of 51 minutes after the trigger; H > 16.0 (Vega; calibrated against the 2MASS catalogue), at a mid-time of 57 minutes after the trigger. View this GCN Circular online at https://gcn.nasa.gov/circulars/40395. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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