September 2025 - vsnet-grb-info - ooruri.kusastro.kyoto-u.ac.jp

[vsnet-grb-info 39743] GRB 250903A: SVOM detection of a burst
by GCN Circulars 03 Sep '25

03 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41677 SUBJECT: GRB 250903A: SVOM detection of a burst DATE: 25/09/03 18:13:40 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Tais Maiolino (LUPM), Claire Guépin-Detrigne (LUPM), Nicolas Dagoneau (CEA/Irfu), Stéphane Schanne (CEA/Irfu), Miguel Moita (CEA/Irfu) report on behalf of the SVOM mission team: At 2025-09-03T17:24:56 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 250903A (SVOM burst-id sb25090304). The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network. The burst was detected both by the Count-Rate Trigger (CRT) and the Image Trigger (IMT), which produced a sequence of 12 alerts. IMT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 16.17 in the [5-20] keV energy band over a time window of 20.48 seconds starting at 2025-09-03T17:24:43. The localization of the best alert is R.A., Dec. 356.9689, -75.9460 degrees: R.A. (J2000) = 23h47m52.54s Dec. (J2000) = -75d56m45.52s with a 90% confidence level (C.L.) radius of 5.17 arcmin (including systematic error of 2 arcmin added in quadrature). This burst was also detected by SVOM/GRM with a significance of 15.80. The SVOM/GRM light curve showed a multi-peak structure with a T90 duration of about 27 (-11/+4)s. SVOM slewed to the burst. No X-ray observation has been performed by SVOM/MXT for the time being. No optical observation has been performed by SVOM/VT for the time being. We notice the presence of BLLac 2FGL J2351.6-7558 located at 12 arcmin from the ECLAIRs position. The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. SVOM/ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC. SVOM/GRM was developed by the Institute of High Energy Physics (IHEP) of CAS. SVOM/MXT was developed jointly by CNES, CEA-IRFU, CNRS-IJCLab, University of Leicester, MPE. The Burst Advocate (BA) on shift for this alert is Tais Maiolino: tais.maiolino(a)lupm.in2p3.fr. Please contact the BA by email if you require additional information. View this GCN Circular online at https://gcn.nasa.gov/circulars/41677. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39742] EP250903a: Global MASTER-Net observations report
by GCN Circulars 03 Sep '25

03 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41676 SUBJECT: EP250903a: Global MASTER-Net observations report DATE: 25/09/03 17:18:36 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 EP250903a ( EP Team et al., GCN 41674) errorbox 4803 sec after notice time and 10720 sec after trigger time at 2025-09-03 17:01:41 UT, with upper limit up to 15.9 mag. Observations started at twilight. The observations began at zenith distance = 60 deg. The sun altitude is -8.9 deg. The galactic latitude b = -56 deg., longitude l = 342 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2983979 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 10751 | 2025-09-03 17:01:41 | MASTER-SAAO | (22h 31m 47.53s , -49d 57m 38.2s) | C | 60 | 15.9 | 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/41676. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39741] EP250903a: TRT optical observations
by GCN Circulars 03 Sep '25

03 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41675 SUBJECT: EP250903a: TRT optical observations DATE: 25/09/03 17:08:34 GMT FROM: J. An <jiean0813(a)foxmail.com> J. An (NAOC), S. Tinyanont, R. Anutarawiramkul, P. Butpan (NARIT), S.Y. Fu (HUST), L.B. He, X. Liu, Z.P. Zhu, S.Q. Jiang, Z. Fan, W.X. Li, N.C. Sun, Y.N. Wang, D. Xu (NAOC) report on behalf of a large collaboration: We observed the field of EP250903a (Zhao et al., GCN 41674), using the 0.7-m telescope of the Thai Robotic Telescope network (TRT), located at New South Wales, Australia (SBO). Observations started at 14:14:31 UTC on 2025-09-03, i.e., ~ 11.5 min after the EP/WXT trigger and a series of frames in the R band were obtained. No uncatalogued source is detected in our stacked image within or at the border of the EP-FXT error circle, down to a 5-sigma limiting magnitude of R > 20.1 (Vega) at ~ 1.21 hr post-trigger, calibrated with SKYMAPPER DR2 catalog and not corrected for Galactic extinction. The two relatively bright catalogued sources/stars within or at the border of the EP-FXT error circle do not show variability in brightness. Our result is consistent with that by GOTO (O'Neill et al., GCN 41672). We note that there are faint galaxies within the EP-FXT error circle from Legacy Survey, so deep follow-ups are encouraged. View this GCN Circular online at https://gcn.nasa.gov/circulars/41675. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39740] EP250903a: Einstein Probe detection of an X-ray transient
by GCN Circulars 03 Sep '25

03 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41674 SUBJECT: EP250903a: Einstein Probe detection of an X-ray transient DATE: 25/09/03 15:41:06 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> T. Zhao, Y. J. Song(NAO, CAS), Y. J. Zhang(THU), H. Sun(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 EP250903a, which was also followed by GOTO (O'Neill et al., GCN 41672). The transient triggered EP-WXT (ID: 01709201159) at 2025-09-03T14:03:01 (UTC). The WXT position of the source is R.A. = 339.120 deg, DEC = -49.863 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. = 339.1097 deg, DEC = -49.8572 deg (J2000) with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic). There are several stars within the FXT error circle. The stellar flare origin for this event can not be fully ruled out at this time. 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/41674. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39739] EP 250827B: Detection of the fading supernova counterpart by LCO.
by GCN Circulars 03 Sep '25

03 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41673 SUBJECT: EP 250827B: Detection of the fading supernova counterpart by LCO. DATE: 25/09/03 15:34:43 GMT FROM: ankur ghosh at CAPP, University of Johannesburg <ghosh.ankur1994(a)gmail.com> Ankur Ghosh, Soebur Razzaque (CAPP, University of Johannesburg), Rahul Gupta (NASA GSFC), Alexander Moskvitin, Yulia Sotnikova (SAO RAS), Naveen Dukiya (ARIES)on behalf of a larger collaboration. We observed the field of the EP250827B/AT 2025wkm (Schroeder et al., GCN 41635) in V, r filter of the 0.4-m SCICAM QHY600 at the Las Cumbres Observatory Global Telescope (LCOGT) node located at Haleakala Observatory, Hawai . The 0.4 m SCICAM QHY600 is equipped with 9576 x 6388 pixel CCD (FOV: 1.9 x 1.2 degrees, scale: 0.74 arcsec/pixel) but we only used the FOV of 30 x 30 arcmin for our observation. Observations began on September 03, 2025, starting 7.32 days after the GRB trigger. Further observations are currently ongoing. We clearly detect the optical transient (OT) reported by GCNs (Schroder et al., GCN 41635; Hall et al., GCN 41636; Hall et al., GCN 41641; Eyles-Ferris et al., GCN 41655; Ma et al., GCN 41667; Eyles-Ferris et al., GCN 41669, He et al,. GCN 41671) in our r band image. Eyles-Ferris et al., GCN 41655 reported the detection of the rise of the associated Ic-BL supernova, with a measured magnitude of 18.91 at 5.61 days after the explosion. The source subsequently faded by ~1 mag within 1.71 days. |Date| |UTstart| |t-T0 (days)| |Exp (sec)| |Filter| |Magnitude| -------------------------------------------------------------------------------------------------- 2025-09-03 13:58:49.728 7.32 3 x 900 r r = 19.81 +/- 0.05 The field was calibrated against nearby APASS stars, with magnitudes converted using Lupton (2005) equations, and has not been corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/41673. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39738] EP/WXT01709201159: GOTO optical follow-up
by GCN Circulars 03 Sep '25

03 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41672 SUBJECT: EP/WXT01709201159: GOTO optical follow-up DATE: 25/09/03 15:13:59 GMT FROM: Ben Gompertz at U of Birmingham <b.gompertz(a)bham.ac.uk> D. O'Neill, M. E. Wortley, B. P. Gompertz, A. Kumar, R. Starling, K. Ackley, M. J. Dyer, J. Lyman, K. Ulaczyk, B. Godson, D. Steeghs, D. K. Galloway, V. Dhillon, P. O'Brien, G. Ramsay, K. Noysena, R. Kotak, R. P. Breton, L. K. Nuttall, and J. Casares report on behalf of the GOTO collaboration: We report on optical observations with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022, Dyer et al. 2024) in response to the EP/WXT trigger number 01709201159. A targeted observation was performed at Sept. 3 2025 14:10:33 UT, (+0.13h post trigger). The images were taken in the GOTO L-band (400-700 nm) and consisted of 4x90s exposures. Images were processed immediately after acquisition using the GOTO pipeline. Difference imaging was performed using deeper template observations. Source candidates were initially filtered using a classifier (Killestein et al. 2021) and cross-matched against a variety of contextual and minor planet catalogs. Human vetting was carried out in real time on any candidates that passed the above checks. We do not identify any candidate optical counterparts within the EP/WXT localisation uncertainty region after the trigger time, down to a 3-sigma limiting magnitude of L > 20.0 AB mag. Additionally, we do not see any evidence for stellar variability consistent with the WXT uncertainty region. Magnitudes were calibrated using ATLAS-REFCAT2 (Tonry et al. 2018) and were not corrected for Galactic extinction. GOTO (https://goto-observatory.org) is a network of telescopes that is principally funded by the STFC and operated at the Roque de los Muchachos Observatory on La Palma, Spain, and Siding Spring Observatory in NSW, Australia, on behalf of a consortium including the University of Warwick, Monash University, Armagh Observatory & Planetarium, the University of Leicester, the University of Sheffield, the National Astronomical Research Institute of Thailand (NARIT), the University of Turku, the University of Portsmouth, the University of Manchester and the Instituto de Astrofisica de Canarias (IAC). View this GCN Circular online at https://gcn.nasa.gov/circulars/41672. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39737] EP250827b / AT 2025wkm: TRT optical observations
by GCN Circulars 03 Sep '25

03 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41671 SUBJECT: EP250827b / AT 2025wkm: TRT optical observations DATE: 25/09/03 15:06:38 GMT FROM: L. B. He at NAOC <helb(a)bao.ac.cn> L.B. He (NAOC), K. Noysena, K. Chanchaiworawit, S. Tinyanont, R. Anutarawiramkul, P. Butpan (NARIT), S.Y. Fu (HUST), J. An, X. Liu, Z.P. Zhu, S.Q. Jiang, Z. Fan, W.X. Li, N.C. Sun, Y.N. Wang, D. Xu (NAOC) report on behalf of a large collaboration: We followed up the optical transient AT 2025wkm, which is potentially associated with EP250827b (Schroeder et al., GCN 41635). Our first epoch was carried out at the 0.7-m telescope of the Thai Robotic Telescope network (TRT), located at Fresno, California, U.S.A (SRO). And we obtained several frames in the R band. The counterpart (Schroder et al., GCN 41635; Hall et al., GCN 41636; Hall et al., GCN 41641; Eyles-Ferris et al., GCN 41655; Ma et al., GCN 41667; Eyles-Ferris et al., GCN 41669) was clearly detected in the stacked image, with R = 19.62 +/- 0.04 (Vega), calibrated with Pan-STARRS DR2 catalog and not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/41671. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39736] EP250827b: NOT spectroscopic observations and AT 2025wkm classification as a broad-lined type-Ic supernova
by GCN Circulars 03 Sep '25

03 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41670 SUBJECT: EP250827b: NOT spectroscopic observations and AT 2025wkm classification as a broad-lined type-Ic supernova DATE: 25/09/03 13:24:21 GMT FROM: Gregory Corcoran at University College Dublin <gregory.corcoran(a)ucdconnect.ie> G. Corcoran (UCD), A. J. Levan (Radboud and Warwick), D. B. Malesani (DAWN/NBI and Radboud), A. Martin-Carrillo (UCD), P. G. Jonker (Radboud), R. A. J. Eyles-Ferris (Leicester), V. Vuolteenaho (NOT and Oulu Univ.), M. Pursiainen (Warwick), I. Worssam (Birmingham) report: We carried out two spectroscopic observations of the optical transient AT 2025wkm (Schroeder et al., GCN 41635) likely associated with the Einstein Probe transient EP250827b, using the ALFOSC spectrograph mounted on the Nordic Optical Telescope (NOT). The observations started on 2025-09-02 at 00:31:54 and 2025-09-03 at 04:37:19 UT for the two epochs, respectively (5.76 and 6.93 days after the EP trigger). Both observations consisted of 4 x 900 s exposures and cover the wavelength range 3800-9500 AA. Both spectra show features consistent with broad-lined type Ic supernovae at a comparable phase, though with an excess of flux on the blue end, providing a good match to the super-luminous SN 2011kl (associated with GRB 111209A; Greiner et al. 2015, doi:10.1038/nature14579) near peak. The brightness of the source, at an absolute magnitude of r = -18.91 and still rising (Eyles-Ferris & Starling, GCN 41669), is currently consistent with classification as both a normal Ic-BL SN and a super-luminous SN. Between the two epochs, we also identify no significant spectral evolution consistent with the constant colour observed by Eyles-Ferris & Starling (GCN 41669). Further photometric and spectroscopic observations are planned and encouraged to better characterize this interesting source. View this GCN Circular online at https://gcn.nasa.gov/circulars/41670. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39735] EP250827b: continued Liverpool Telescope observations
by GCN Circulars 03 Sep '25

03 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41669 SUBJECT: EP250827b: continued Liverpool Telescope observations DATE: 25/09/03 12:19:38 GMT FROM: Rob Eyles-Ferris at U of Leicester <raje1(a)leicester.ac.uk> R. A. J. Eyles-Ferris and R. L. C. Starling (U of Leicester) report on behalf of a larger collaboration: We observed the position of EP250827b/AT 2025wkm (Schroeder et al., GCN 41635) with the 2m Liverpool Telescope using the IO:O instrument. We obtained a series of exposures in the SDSS u’g’r’i’z’ filters starting at 2025-09-03 01:45:07 UT, approximately 162.5 hours after the X-ray detection. We performed image subtraction on the stacked g’r’i’z’ images using reference images from Pan-STARRS. AT 2025wkm is clearly detected in all our subtractions and appears to be currently rising in all bands. We measure r’ = 19.90 +/- 0.05, calibrated to Pan-STARRS and not corrected for Galactic extinction, which corresponds to an absolute magnitude of -18.91 adopting the redshift of 0.120 of Sevilla and Ho (GCN 41639). We note no significant change in colour (g’ - r’ ~ 0) when compared with our earlier epoch photometry (Eyles-Ferris and Starling, GCN 41655). Further observations are planned. View this GCN Circular online at https://gcn.nasa.gov/circulars/41669. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39734] GRB 250902B: SVOM/GRM observation
by GCN Circulars 03 Sep '25

03 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41668 SUBJECT: GRB 250902B: SVOM/GRM observation DATE: 25/09/03 11:23:57 GMT FROM: Chenwei Wang at IHEP <cwwang(a)ihep.ac.cn> SVOM/GRM team: Chen-Wei Wang, Yue Huang, Shi-Jie Zheng, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Feliu Lacreu (IAP) Report on behalf of the SVOM team: SVOM/GRM was triggered in-flight by a burst GRB 250902B (SVOM trigger reference: sb25090205) at 2025-09-02T18:45:36.000 UTC (T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN #41660). With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of multi-pulses with a T90 of 17.4 +1.3/-0.7 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb250902B.png In addition, the position of this burst, as determined by Fermi/GBM (RA = 82.3, Dec = -5.0, GCN #41660), is located at about 85 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view. With the localization from Fermi/GBM, the time-averaged spectrum from T0-10 to T0+20 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -0.85 +0.18/-0.17 and the cutoff energy, parameterized as Epeak, is 146 +21/-16 keV. The event fluence (10-1000 keV) in this time interval is (1.07 +0.08/-0.07)E-05 erg/cm^2. The 'Amati' relation diagram of GRB 250902B is shown at: https://www.bursthub.cn//admin/static/svgrb250902B_amati.png The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. GRM is developed by the Institute of High Energy Physics (IHEP) of CAS. The SVOM point of contact for this burst is: Chen-Wei Wang (IHEP)(cwwang(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/41668. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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