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

[vsnet-grb-info 39843] GRB 250910A / EP250910a: VLT/HAWK-I near-infrared observations
by GCN Circulars 10 Sep '25

10 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41777 SUBJECT: GRB 250910A / EP250910a: VLT/HAWK-I near-infrared observations DATE: 25/09/10 11:26:08 GMT FROM: Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani(a)nbi.ku.dk> M. Garnichey (LUX-Paris Obs.), V. D'Elia (ASI-SSDC), B. Schneider (LAM), A. J. Levan (Radboud U.), D. B. Malesani (DAWN/NBI and Radboud), A. Martin-Carrillo (UCD), A. Saccardi (CEA/Irfu), A. L. Thakur (INAF-IAPS), S. D. Vergani (LUX-Paris Obs.) report on behalf the Stargate collaboration: We observed the field of GRB 250910A / EP250910a (Ma et al., GCN 41769; Götz et al. GCN 41770; Wu et al., GCN 41772; Li et al., GCN 41774; Liu et al., GCN 41776) using the ESO VLT UT4 (Yepun) equipped with the HAWK-I NIR camera. We obtained 15 min imaging in the J band, beginning on 2025-09-10 at 08:28 UT (5.2 hr post-trigger). Within the 20"-radius EP/FXT error circle (Liu et al., GCN 41776), several objects are visible in the stack of our data. All have an archival optical counterpart in the Legacy Survey (and they are thus not high-redshift candidates). Any of these sources could in principle contain an afterglow contribution, but a new template image is required to isolate any transient flux that might be present in our image. Further observations are planned with HAWK-I. We acknowledge excellent support from the ESO observing staff in Paranal, in particular Julien Drevon. View this GCN Circular online at https://gcn.nasa.gov/circulars/41777. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39842] EP250910a/GRB 250910A: EP-WXT detection of a fast X-ray transient
by GCN Circulars 10 Sep '25

10 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41776 SUBJECT: EP250910a/GRB 250910A: EP-WXT detection of a fast X-ray transient DATE: 25/09/10 09:08:42 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Q. C. Liu (THU), H. N. Yang, H. W. Pan (NAO,CAS) on behalf of the Einstein Probe team: We report on the detection of a fast X-ray transient, designated EP250910a, by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission. The transient event started at 2025-09-10T03:16:04 (UTC). The position of the source is R.A. = 39.797 deg, DEC = -39.686 deg (J2000) with an uncertainty of 2.1 arcmin in radius (90% C.L. statistical and systematic). The trigger time and position of this X-ray transient are consistent with that of GRB 250910A (GCN 41769, GCN 41770). The 0.5-4 keV spectrum can be fitted with an absorbed power law with a Galactic hydrogen column density of 1.74 x 10^20 cm^-2 and a photon index of 0.8 (+0.3/-0.3) during the flare. The estimated unabsorbed 0.5-4 keV flux of the flare is 1.2 (+0.3/-0.2) x 10^(-9) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. The transient event lasts for 160 seconds. A follow-up observation with the Follow-up X-ray Telescope (FXT) was performed. Within the WXT error circle, an uncatalogued X-ray source was detected at R.A. = 39.8048 deg, DEC = -39.6966 deg (J2000) with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic). Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). View this GCN Circular online at https://gcn.nasa.gov/circulars/41776. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39841] GRB 250909B: AstroSat CZTI detection of a long burst
by GCN Circulars 10 Sep '25

10 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41775 SUBJECT: GRB 250909B: AstroSat CZTI detection of a long burst DATE: 25/09/10 08:58:31 GMT FROM: Anuraag Arya at IIT Bombay <aryaanuraag910(a)gmail.com> M. Tembhurnikar (IUCAA), Harsha K. H. (IUCAA), S. Salunke (IUCAA), A. Arya (IITB), A. Goyal (IITB), G. Waratkar (Caltech/IITB), A. Vibhute (IUCAA), V. Bhalerao (IITB), D. Bhattacharya (Ashoka University/IUCAA), A. R. Rao (IUCAA/TIFR), and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration: Analysis of AstroSat CZTI data with the CIFT framework (Sharma et al., 2021, JApA, 42, 73) showed the detection of a long and bright GRB 250909B which was also detected by Konus-Wind (IPN notices). The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2025-09-09 17:49:11.50 UTC. The measured peak count rate associated with the burst is 701 (+50, -52) counts/s above the background in the combined data of all quadrants, with a total of 3971 (+218, -234) counts. The local mean background count rate was 282 (+4, -4) counts/s. Using cumulative rates, we measure a T90 of 10.1 (+0.9, -0.4) s. The source was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2025-09-09 17:49:10.32 UTC. The measured peak count rate associated with the burst is 1432 (+86, -93) counts/s above the background in the combined data of all quadrants, with a total of 5850 (+337, -369) counts. The local mean background count rate was 1344 (+7, -8) counts/s. We measure a T90 of 9.4 (+0.5, -0.3) s from the cumulative Veto light curve. CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, URSC, IUCAA, SAC, and PRL. The Indian Space Research Organisation funded, managed, and facilitated the project. CZTI GRB detections are reported regularly on the payload site at: http://astrosat.iucaa.in/czti/?q=grb View this GCN Circular online at https://gcn.nasa.gov/circulars/41775. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39840] GRB 250910A: SVOM/VT optical upper limit
by GCN Circulars 10 Sep '25

10 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41774 SUBJECT: GRB 250910A: SVOM/VT optical upper limit DATE: 25/09/10 08:53:25 GMT FROM: Yinuo Ma <mayn(a)bao.ac.cn> H. L. Li, Y. N. Ma, Z. H. Yao, L. P. Xin, Y. L. Qiu, C. Wu, X. H. Han, Y. Xu, J. Wang, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. S. Deng, J. Y. Wei, D. H. Zhao (NAOC), J. Palmerio (CEA) report on behalf of the SVOM/VT team. SVOM performed an automatic slew on the burst triggered by SVOM/ECLAIRs (Ma et al., GCN 41769). SVOM/VT began observing the field at 2025-09-10T04:00:48 UTC, 0.739 hours after T0, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. No credible candidate was detected in our single or stacked images at the SVOM/MXT position (Götz et al., GCN 41770), the three sigma limits are: mid-time | exposure time (s) | band | upper limit (AB) ---------|-------------------|------|----------------- 1.08h | 16*50 | VT_B | 22.8 1.08h | 16*50 | VT_R | 23.3 Our results are consistent with LCO (Wu et al., GCN 41772). 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/41774. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39839] EP250908C: GROND observation of the fading optical counterpart
by GCN Circulars 10 Sep '25

10 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41773 SUBJECT: EP250908C: GROND observation of the fading optical counterpart DATE: 25/09/10 08:48:05 GMT FROM: Arne Rau at MPE <arau(a)mpe.mpg.de> Arne Rau (MPE) reports: We observed the position of EP250908C (Zhang et al., GCN 41754) using the Gamma-Ray burst Optical Near-infrared Detector (GROND, Greiner et al. 2008) mounted to the MPG 2.2m telescope at ESO’s La Silla Observatory on 2025-09-10 07:24 UT, i.e. 31.5 hours after the Einstein Probe trigger. The candidate optical counterpart reported by Malesani et al. (GCN 41760) was detected with r’= 23.0+/-0.2 i’ = 22.8+/-0.2 indicating clear fading. The magnitudes are in the AB magnitude system and calibrated against nearby SkyMapper sources. We acknowledge the excellent support of the 2.2m staff, in particular Angel Hempel. View this GCN Circular online at https://gcn.nasa.gov/circulars/41773. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39838] GRB 250910A: LCO optical upper limit
by GCN Circulars 10 Sep '25

10 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41772 SUBJECT: GRB 250910A: LCO optical upper limit DATE: 25/09/10 07:43:10 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> C. Wu (NAOC), A. Saccardi (CEA/Irfu), L. P. Xin (NAOC), J. T. Palmerio (CEA/Irfu), B. Cordier (CEA/Irfu), Y. N. Ma (NAOC), D. Zhao (NAOC) report on behalf of the SVOM mission team: We observed the field of the GRB 250910A detected by SVOM/ECLAIRs (Ma et al., GCN 41769) with the LCO 1m telescope at Cerro Tololo Interamerican Observatory equipped with the Sinistro instrument. Our observation started on 2025-09-10 at 05:03:46 UT (~1.79 hr after the trigger) and we obtained 3x200 s exposures using the SDSS r filter. In the stacked image, we did not detect any new optical source at the SVOM/MXT position (Götz et al., GCN 41770). We derived the following upper limit r > 20.8 mag (5-sigma) calibrated using nearby stars from the UCAC4 catalog and not corrected for Galactic extinction. This project is funded by the SVOM collaboration. View this GCN Circular online at https://gcn.nasa.gov/circulars/41772. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39837] GRB 250909A: AstroSat CZTI detection
by GCN Circulars 10 Sep '25

10 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41771 SUBJECT: GRB 250909A: AstroSat CZTI detection DATE: 25/09/10 06:35:24 GMT FROM: Anuraag Arya at IIT Bombay <aryaanuraag910(a)gmail.com> A. Goyal (IITB), A. Arya (IITB), M. Tembhurnikar (IUCAA), Harsha K. H. (IUCAA), S. Salunke (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 250909A which was also detected by Fermi GBM (Fermi GBM Team, GCN Circ. 41753). The source was detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve showed a burst peak of emission at 2025-09-09 02:33:32.44 UTC. The measured peak count rate associated with the burst is 228 (+61, -66) counts/s above the background in the combined data of all quadrants, with a total of 663 (+255, -303) counts. The local mean background count rate was 1258 (+7, -5) counts/s. We measure a T90 of 8.2 (+2.5, -4.0) s from the cumulative Veto light curve. The source was also faintly detected in the CZT detectors in the 20-200 keV energy range. 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/41771. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39836] GRB 250910A: SVOM/MXT possible afterglow detection
by GCN Circulars 10 Sep '25

10 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41770 SUBJECT: GRB 250910A: SVOM/MXT possible afterglow detection DATE: 25/09/10 06:18:14 GMT FROM: Diego Gotz at CEA <diego.gotz(a)cea.fr> D. Götz (CEA), C. Van Hove (IJCLab), M. Moita (CEA) F. Robinet (IJCLab), P. Maggi (ObAS), H. Goto (Kanazawa Univ./CEA), C. Plasse (CEA) , report of behalf of the SVOM/MXT Team: GRB 250910A (Ma et al. GCN# 41769) was observed by SVOM/MXT after an automatic SVOM slew, but due to Earth constraints the observation started at 2025-09-10T05:37:38, about 88 minutes after Tb. Using the on board automatic detection software, MXT detects a faint source at the coordinates R.A. (J2000) = 02h39m18s, Dec (J2000) = -39d39m39s with a 90% C.L. radius of 2.5 arc min (including 25 arc sec systematic error added in quadrature). This position is at 2.8 arc min from the ECLAIRs position. At this time we cannot evaluate the variability of the source. We hence encourage follow-up with other X-ray facilities. The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. MXT was developed jointly by CEA, CNES, University of Leicester, IJCLab and MPE. The Burst Advocate (BA) on shift for this alert is Yinuo Ma: mayn(a)bao.ac.cn. Please contact the BA by email if you require additional information. View this GCN Circular online at https://gcn.nasa.gov/circulars/41770. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39835] GRB 250910A: SVOM detection of a faint burst
by GCN Circulars 10 Sep '25

10 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41769 SUBJECT: GRB 250910A: SVOM detection of a faint burst DATE: 25/09/10 04:10:10 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Yinuo MA, Donghua ZHAO, Wenjin XIE (NAOC), Li ZHANG (IHEP), Charlotte VAN HOVE(IJCLab) report on behalf of the SVOM mission team: At 2025-09-10T03:16:30 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 250910A (SVOM burst-id sb25091001). The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network. The burst was detected both by the Count-Rate Trigger (CRT) and the Image Trigger (IMT), which produced a sequence of 8 alerts. IMT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 8.02 in the [5-20] keV energy band over a time window of 40.96 seconds starting at 2025-09-10T03:16:10. The localization of the best alert is R.A., Dec. 39.7665, -39.6758 degrees: R.A. (J2000) = 2h39m03.96s Dec. (J2000) = -39d40m32.94s with a 90% confidence level (C.L.) radius of 9.80 arcmin (including systematic error of 2 arcmin added in quadrature). SVOM/GRM had no significant detection. SVOM slewed to the burst. SVOM/MXT and SVOM/VT were occulted by the Earth. 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 Yinuo Ma: mayn(a)bao.ac.cn. Please contact the BA by email if you require additional information. View this GCN Circular online at https://gcn.nasa.gov/circulars/41769. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39834] LIGO/Virgo/KAGRA S250910b: Retraction of GW compact binary merger candidate
by GCN Circulars 10 Sep '25

10 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41768 SUBJECT: LIGO/Virgo/KAGRA S250910b: Retraction of GW compact binary merger candidate DATE: 25/09/10 00:42:32 GMT FROM: Trang Nguyen <trang.nguyen(a)ligo.org> The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report: The trigger S250910b is no longer considered to be a candidate of interest. This candidate was initially identified by one or more early-warning analyses by matching partial signal templates to the data. Analysis of additional data up to the putative merger time, with full signal templates, did not make a significant detection, indicating that the initial candidate was likely due to transient noise. View this GCN Circular online at https://gcn.nasa.gov/circulars/41768. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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