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

[vsnet-grb-info 39753] GRB 250902A: GECAM-B detection
by GCN Circulars 04 Sep '25

04 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41687 SUBJECT: GRB 250902A: GECAM-B detection DATE: 25/09/04 02:48:15 GMT FROM: zhengchao_astro(a)foxmail.com Chao Zheng, Chen-Wei Wang, Shao-Lin Xiong and Yue Huang (IHEP) report on behalf of GECAM team: GECAM-B was triggered on-ground by GRB 250902A at 2025-09-02T01:30:00.550 UTC (denoted as T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN #41648) and SVOM/GRM (Wang et al., GCN #41653). According to the GECAM-B light curves in about 40-6000 keV, this burst mainly consists of a multi-pulses with a duration (T90) of 10.5 +1.0/-1.5 s. The GECAM-B light curve can be found here: https://www.bursthub.cn//admin/static/gecambgrb250902A.png GECAM-B localized this burst to the following position (J2000): Ra: 166.6 deg Dec: 20.5 deg Err: 0.7 deg (1-sigma, statistical only) The time-averaged spectrum from T0-2 s to T0+15 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.15 +0.14/-0.14 and the cutoff energy, parameterized as Epeak, is 185 +23/-16 keV. The event fluence (10-1000 keV) in this time interval is (2.69 +/-0.19)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/41687. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39752] GRB 250903A: LCO optical observation
by GCN Circulars 04 Sep '25

04 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41686 SUBJECT: GRB 250903A: LCO optical observation DATE: 25/09/04 01:48:35 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> A. Saccardi (CEA/Irfu), L. P. Xin (NAOC), C. Wu (NAOC), B. Cordier (CEA/Irfu), report on behalf of the SVOM mission team: We observed the field of the GRB 250903A detected by SVOM/ECLAIRs (Maiolino et al., GCN 41677) with the LCO 1m telescope at South African Astronomical Observatory equipped with the Sinistro instrument. Our observation started on 2025-09-03 at 23:25:00 UT (6.0 hr after the trigger) and we obtained 4x300 s exposures using the SDSS r filter. In the stacked image, we detected the optical afterglow (An et al., GCN 41679, Xin et al., GCN 41684, Pérez-Fournon et al. GCN 41685) within the errorbox of SVOM/MXT (Gotz et al., GCN 41681). We derived the following magnitude r = 20.04 +/- 0.11 mag calibrated by the Guide Star Catalog, Version 2.3.2 (GSC2.3) (STScI, 2006) 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/41686. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39751] GRB 250903A: LCO optical afterglow detection
by GCN Circulars 03 Sep '25

03 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41685 SUBJECT: GRB 250903A: LCO optical afterglow detection DATE: 25/09/03 21:28:52 GMT FROM: Ismael Perez-Fournon at Instituto de Astrofisica de Canarias <ipf(a)iac.es> I. Pérez-Fournon, F. Poidevin (IAC and ULL), D. Cano-Morales, A.E. Hernández-Díaz, I. Correa-Plasencia (ULL), and A. López-Oramas (IAC and ULL) We observed the field of GRB 250903A detected by SVOM/ECLAIRs (Maiolino et al., GCN 41677) and SVOM/MXT (Götz et al., GCN 41681) with one of the two 1-m telescopes of the Las Cumbres Observatory Global Telescope network (LCO) equipped with Sinistro cameras located at the LCO node at Siding Spring Observatory, Australia. The observation, of 300 seconds in the SDSS-r filter, started at 2025-09-03 19:12:07 UT, about 1.78 hr after the SVOM/ECLAIRs trigger. We clearly detect an uncatalogued source within the SVOM/ECLAIRs (Maiolino et al., GCN 41677) and SVOM/MXT (Götz et al., GCN 41681) error circles at a position consistent with the one reported by An et al. (TRT R band, GCN 41679) and Xin et al. (SVOM/VT VT_B and VT_R, GCN 41684). We measure a magnitude of r = 20.29 +/- 0.10, calibrated with the Legacy Surveys DR10 catalog and not corrected for Galactic extinction. This work makes use of observations from the Las Cumbres Observatory global telescope network program IAC2025B-008 (SGLF). View this GCN Circular online at https://gcn.nasa.gov/circulars/41685. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39750] GRB 250903A: SVOM/VT optical confirmation with VHF data
by GCN Circulars 03 Sep '25

03 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41684 SUBJECT: GRB 250903A: SVOM/VT optical confirmation with VHF data DATE: 25/09/03 21:14:00 GMT FROM: Liping Xin at NAOC, SVOM <xlp(a)nao.cas.cn> L.P. Xin, H.L. Li, C. Wu. Y. L. Qiu, Z.H. Yao, Y.N. Ma, X.H. Han, J. Wang, W.J. Xie, Y. Xu, H.B. Cai, J. Y. Wei (NAOC), J. Palmerio (CEA), Tais Maiolino (LUPM), Claire Guépin-Detrigne (LUPM) report on behalf of the SVOM team. SVOM/VT performed an automatic slew on the burst triggered by SVOM/ECLAIRs (Maiolino et al. GCN 41677). SVOM/VT began observing the field automatically at 2025-09-03T18:15:57 UTC, about 52 min after the T0, with the slew of the platform triggered on-board, in VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. With downlinked VHF data, the optical counterpart reported (An et al., GCN 41679) within the errorbox of SVOM/MXT (GOTZ et al., GCN 41681) was clear detected with the brightness of VT_B=20.12+/-0.03 and VT_R=19.65 +/-0.03 mag at 54.5 min after the trigger. More follow-ups 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/41684. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39749] EP250903a: SVOM/VT optical confirmation
by GCN Circulars 03 Sep '25

03 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41683 SUBJECT: EP250903a: SVOM/VT optical confirmation DATE: 25/09/03 20:50:43 GMT FROM: Liping Xin at NAOC, SVOM <xlp(a)nao.cas.cn> L. P. Xin, H. L. Li, Y. N. Ma, Y. L. Qiu, C. Wu, Z. H. Yao, Y. Xu, J. Wang, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA) report on behalf of the SVOM/VT team. SVOM performed a Target of Opportunity observations of EP250903a detected by EP/WXT (Zhao et al., GCN 41674). The observations was started from 2025-09-03T15:01:54 UTC, 58 min after the EP trigger time, in VT_B (400-650 nm) and VT_R (650-1000nm) bands simultaneously. . The optical source reported (Levan et al., GCN 41680) was clear detected in VT stacked images. The brightness was VT_B=22.1+/-0.1 and VT_R=21.5+/-0.1 mag at the mid time of 1.1 hours after the trigger. Our photometry is 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/41683. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39748] EP250901a: Mondy, Assy and SAO RAS optical limits
by GCN Circulars 03 Sep '25

03 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41682 SUBJECT: EP250901a: Mondy, Assy and SAO RAS optical limits DATE: 25/09/03 20:14:49 GMT FROM: Alexander Moskvitin at SAO RAS <mosk(a)sao.ru> A. Moskvitin (SAO RAS), A. Pozanenko (IKI), E. Klunko (ISTP), V. Kim, M. Krugov (FAI), O. Spiridonova (SAO RAS) report on behalf of GRB follow-up team and IKI-GRB-FuN: We observed the field of EP250901a (Song et al., GCNs 41627, 41651) with the 1.5m AZT-33IK telescope of the Solar Sayan Observatory (Mondy), 1.5m AZT-20 telescope of Assy Observatory and 1.0m Zeiss-1000 telescope of SAO RAS during the night of September 1. Within the refined FXT error circle (Song et al., GCN 41651) we didn't detect any new objects down to the following limits. UT_start t_mid-T0, h exp, s filter up.lim telescope FWHM 13:51:06 2.250997 30 x 120 R 23.2 Mondy, AZT-33IK 2".0 16:17:59 4.837000 61 x 60 r 22.8(AB) Assy, AZT-20 2".6 16:57:33 5.231111 14 x 120 Rc 22.4 SAO, Zeiss-1000 2".1 These preliminary results are in an agreement with the limits from MASTER (Lipunov et al., GCN 41629) and Mephisto (Liu et al., GCN 41631). In the stacked R band image of AZT-33IR within FXT error circle localization (Song et al., GCN 41651) we detected two objects, both presented in the PanSTARRS DR1 images and PS1 catalog, the 1st one is also visible in z-band image of the Legacy Survey DR10. obj. R. A. Decl. (J2000) R_mag +/- err #1 18:12:10.03 +18:42:25.0 22.5 +/- 0.2 #2 18:12:09.78 +18:42:28.3 23.2 +/- 0.3 Also in the stacked image of AZT-33IK we detected one object near the border of XRT circle (SWIFT J181210.9+184216; Evans et al., GCN 41644) with the coordinates of R. A. (J2000) = 18:12:11.02 Decl. (J2000) = +18:42:23.1 with uncertainness of +/- 0".4 in both coordinates, and brightness of R = 22.39 +/- 0.16. This object is presented in the PanSTARRS DR1 images and catalog. The field was calibrated with nearby stars from the PanSTARRS DR1 catalog and not corrected for Galactic extinction. RA DEC r err R err 273.042629860 18.705792060 18.284 0.004 18.048 0.009 273.048977320 18.703099150 17.400 0.004 17.204 0.008 273.046825830 18.696310020 19.130 0.017 18.940 0.017 View this GCN Circular online at https://gcn.nasa.gov/circulars/41682. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39747] Subject GRB 250903A: SVOM/MXT afterglow detection
by GCN Circulars 03 Sep '25

03 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41681 SUBJECT: Subject GRB 250903A: SVOM/MXT afterglow detection DATE: 25/09/03 19:02:33 GMT FROM: Diego Gotz at CEA <diego.gotz(a)cea.fr> D. Götz (CEA), M. Moita (CEA) F. Robinet (IJCLab), P. Maggi (ObAS), H. Goto (Kanazawa Univ./CEA), C. Plasse (CEA) , C. Van Hove (IJCLab) report of behalf of the SVOM/MXT Team: GRB 250903A (Maiolino et al. GCN# 41677) was observed by SVOM/MXT after an automatic SVOM slew, but due to Earth constraints the observation started at 2025-09-03T18:30:41, about 66 minutes after Tb. Using the on board automatic detection software, MXT detects a faint source at the coordinates R.A. (J2000) = 23h47m21s Dec (J2000) = -75d58m43s with a 90% C.L. radius of 3 arc min (including 25 arc sec systematic error added in quadrature). This position is at 3.1 arc min from the ECLAIRs position and 0.5 arc min from the optical counterpart reported by An et al. (GCN# 41679). We hence identify this source as the X-ray afterglow of GRB 250903A. Further analysis will be perfromed once the full X-band data set is received. The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. MXT was developed jointly by CEA, CNES, University of Leicester, IJCLab and MPE. The SVOM point of contact for this burst is Tais Maiolino: tais.maiolino(a)lupm.in2p3.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/41681. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39746] EP250903a: LCO candidate counterpart discovery
by GCN Circulars 03 Sep '25

03 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41680 SUBJECT: EP250903a: LCO candidate counterpart discovery DATE: 25/09/03 18:47:51 GMT FROM: Andrew Levan at Radboud University <a.levan(a)astro.ru.nl> A. J. Levan (Radboud and Warwick), J. A. Quirola-Vasquez (Radboud), D. B. Malesani (DAWN/NBI and Radboud), G. Corcoran (UCD), A. Martin-Carrillo (UCD), R. A. J. Eyles-Ferris (Leicester), P. G. Jonker (Radbound), F. E. Bauer (SSI and UTA), and J. Chacón (PUC) report on behalf of a larger collaboration: We observed the location of EP250903a (Zhao et al. GCN 41674) with the Sinistro instrument mounted on the 1-m telescopes at the LCO Siding Springs Observatory. 3 x 300 s exposures were obtained in the SDSS r filter at a start time of 14:44:15 UT on 2025-09-03 (~41 minutes post trigger). Within the WXT and FXT error circles we locate a new source in our stacked r-band image with r~21 mag (AB) calibrated against nearby SkyMapper stars and not corrected by Galactic extinction, at a location of RA(J2000): 22:36:27.75 DEC(J2000): -49:51:25.6 The error is about 0.5” in each coordinate. We note the transient is offset ~1” from a Legacy survey object with magnitude r= 21.49 mag which has a photometric redshift of 0.24 +/- 0.11. In the legacy images the source appears to extend underneath the new source. Thus, our photometry likely includes some contribution from the host galaxy. View this GCN Circular online at https://gcn.nasa.gov/circulars/41680. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39745] GRB 250903A: TRT optical counterpart detection
by GCN Circulars 03 Sep '25

03 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41679 SUBJECT: GRB 250903A: TRT optical counterpart detection DATE: 25/09/03 18:46:15 GMT FROM: J. An <jiean0813(a)foxmail.com> J. An (NAOC), K. Noysena, K. Chanchaiworawit, S. Tinyanont (NARIT), S.Y. Fu (HUST), L.B. He, X. Liu, Z.P. Zhu, S.Q. Jiang, D. Xu (NAOC) report on behalf of a large collaboration: We observed the field of GRB 250903A detected by SVOM/ECLAIRs (Maiolino et al., GCN 41677), using the 0.7-m telescope of the Thai Robotic Telescope network (TRT), located at New South Wales, Australia (SBO). Observations started at 17:34:50 UTC on 2025-09-03, i.e., ~10 min after the SVOM/ECLAIRs trigger. A series of R-band frames were obtained. An uncatalogued and varying optical source is detected within the SVOM/ECLAIRs error circle (Maiolino et al., GCN 41677), at coordinates R.A. (J2000) = 23:47:11.67 Dec. (J2000) = -75:58:00.21 with an uncertainty of ~ 0.8 arcsec. Preliminary photometry shows the source has R ~ 19.0 mag at 13.35 min post-trigger, calibrated with Legacy Survey DR10 catalog and not corrected for Galactic extinction. We think the source is the optical counterpart of GRB 250903A. View this GCN Circular online at https://gcn.nasa.gov/circulars/41679. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39744] GRB 250902B: AstroSat CZTI detection
by GCN Circulars 03 Sep '25

03 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41678 SUBJECT: GRB 250902B: AstroSat CZTI detection DATE: 25/09/03 18:16:21 GMT FROM: Anuraag Arya at IIT Bombay <aryaanuraag910(a)gmail.com> M. Tembhurnikar (IUCAA), A. Arya, (IITB), G. Waratkar (IITB), A. Vibhute (IUCAA), V. Bhalerao (IITB), D. Bhattacharya (Ashoka University/IUCAA), A. R. Rao (IUCAA/TIFR), and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration: Analysis of AstroSat CZTI data with the CIFT framework (Sharma et al., 2021, JApA, 42, 73) showed the detection of a GRB 250902B which was also detected by Fermi GBM (Fermi GBM Team, GCN Circ. 41660), and SVOM GRM (Wang et. al., GCN Circ. 41668). 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 2025-09-02 18:45:45.00 UTC. The measured peak count rate associated with the burst is 47 (+17, -10) counts/s above the background in the combined data of two quadrants (out of four), with a total of 297 (+122, -145) counts. The local mean background count rate was 152 (+2, -2) counts/s. Using cumulative rates, we measure a T90 of 17.2 (+2.7, -7.6) s. The source was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2025-09-02 18:45:44.68 UTC. The measured peak count rate associated with the burst is 365 (+71, -49) counts/s above the background in the combined data of all quadrants, with a total of 1924 (+390, -422) counts. The local mean background count rate was 1405 (+5, -6) counts/s. We measure a T90 of 15.4 (+3.2, -2.4) s from the cumulative Veto light curve. CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, URSC, IUCAA, SAC, and PRL. The Indian Space Research Organisation funded, managed, and facilitated the project. CZTI GRB detections are reported regularly on the payload site at: http://astrosat.iucaa.in/czti/?q=grb View this GCN Circular online at https://gcn.nasa.gov/circulars/41678. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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