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

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

16 Sep '25

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

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

16 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41836 SUBJECT: SVOM/sb25091517: Confirmation of a stellar flare by SVOM/VT DATE: 25/09/16 07:10:53 GMT FROM: Huali Li at at NAOC, SVOM <lhl(a)nao.cas.cn> H.L. Li (NAOC), L.P. Xin, Y. N. Ma, Y.L. Qiu, C. Wu, Z.H. Yao, X.H. Han, J. Wang, W.J. Xie, Y. Xu, H.B. Cai, J.Y. Wei (NAOC), J. Palmerio (CEA), Y. Julakanti, R. A. J. Eyles-Ferris (U. Leicester) report on behalf of the SVOM team. SVOM performed an automatic slew on the soft burst triggered by SVOM/ECLAIRs (Julakanti et al., GCN 41834) in VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. The observation with good image quality began at 2025-09-15T22:09:18, i.e., 457 sec post trigger. With X band downlinked data, preliminary analysis shows that the M2 dwarf 1RXS J020013.6-084106 located within MXT's errorbox (Julakanti et al., GCN 41834) was decreasing in brightness from 10.6 mag to 12.2 mag in VT_B during 3 hour time interval after the trigger time. This result confirms that the trigger was due to a stellar flare, as already reported by Jelinek et al. (GCN 41617). Our photometry was estimated in AB magnitude. The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS. View this GCN Circular online at https://gcn.nasa.gov/circulars/41836. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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

16 Sep '25

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

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

15 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41834 SUBJECT: SVOM/sb25091517: SVOM detection of an X-ray transient DATE: 25/09/15 23:23:46 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Y. Julakanti, R. A. J. Eyles-Ferris (U. Leicester), S. Schanne (CEA/Irfu), F. Piron (LUPM), H. Goto (Kanazawa Univ./CEA), report on behalf of the SVOM mission team: At 2025-09-15T22:01:41 UTC (T0), SVOM/ECLAIRs triggered and located the X-ray transient SVOM/sb25091517 (SVOM burst-id). The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network. The burst was only detected by the Image Trigger (IMT), which produced a sequence of 3 alerts. IMT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 8.81 in the [5-20] keV energy band over a time window of 655.36 seconds starting at 2025-09-15T21:56:13 (Tb). The localization of the best alert is R.A., Dec. 30.1388, -8.7614 degrees (J2000) with a 90% confidence level (C.L.) radius of 8.96 arcmin (including systematic error of 2 arcmin added in quadrature). We notice the presence of the known X-ray sources 6dFGS gJ020039.1-084555, 2E 0157.9-0853, 1RXS J020013.6-084106, CXOMP J020012.1-085113 in the ECLAIRs error box. SVOM slewed to the burst. SVOM/MXT began observing the field at 2025-09-15T22:09:15 UTC, 454 seconds after T0. Using onboard processed data we found an X-ray source located at R.A., Dec. 30.0581, -8.6826 degrees: R.A. (J2000) = 2h00m13.94s Dec. (J2000) = -8d40m57.37s with a 90% C.L. radius of 30 arcseconds. This location is 6.73 arcminutes from the ECLAIRs onboard position. This position may be improved as more data is received. We notice that the High Proper Motion Star 1RXS J020013.6-084106 is located at 18 arcsec from the MXT position. Therefore this trigger is likely caused by a flare from this star. VT began observing the field after the slew. The analysis of the data will be published in a future circular. The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. SVOM/ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC. SVOM/GRM was developed by the Institute of High Energy Physics (IHEP) of CAS. SVOM/MXT was developed jointly by CNES, CEA-IRFU, CNRS-IJCLab, University of Leicester, MPE. The Burst Advocate (BA) on shift for this alert is Yashaswi Julakanti: skyj1(a)leicester.ac.uk. Please contact the BA by email if you require additional information. View this GCN Circular online at https://gcn.nasa.gov/circulars/41834. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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

15 Sep '25

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

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

14 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41832 SUBJECT: GRB 250912A: SVOM/COLIBRÍ (FM-GFT) optical observations DATE: 25/09/14 15:36:39 GMT FROM: Alan Watson at UNAM <alan(a)astro.unam.mx> Alan M. Watson (UNAM), Sarah Antier (OCA), Damien Dornic (CPPM), Benjamin Schneider (LAM), Rosa L. Becerra (U Roma), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Nathaniel R. Butler (ASU), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), N. A. Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), and Antonio de Ugarte Postigo (LAM) report: We imaged the field of the SVOM/Fermi GRB 250912A (Ducoin et al., GCN Circ. 41820, and Fermi GBM Team, GCN Circ. 41819) using the DDRAGO two-channel wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope. We observed from 2025-09-13 05:51 to 08:33 UTC (from 8.75 to 11.45 hours after the ECLAIRs trigger) and obtained 112 minutes of simultaneous exposure in the r and z filters and then again from 2025-09-14 05:52 to 08:10 UTC (from 32.78 to 35.07 hours after the ECLAIRs trigger) and obtained 96 minutes of simultaneous exposure in the r and z filters. The data were reduced and coadded with the COLIBRÍ pipeline and analyzed with STDWeb/STDPipe (Karpov 2025). The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction. We do not detect the J-band source reported by Garnichey et al. (GCN Circ. 41929) and Ricci et al. (GCN Circ. 41830) to 3-sigma limits at our first epoch of: r > 24.8 z > 23.7 and at our second epoch of: r > 24.7 z > 23.5 This confirms the absence of a similarly bright optical counterpart to the J-band source and confirms its extremely red colors. We have subtracted our two epochs and in the difference image find no clear evidence for an optical transient in the MXT error region (Ducoin et al., GCN Circ. 41820) at our first epoch to 5-sigma limits of: r > 23.9 z > 22.8 Our result is in agreement with earlier observations reported by Lipunov et al. (GCN Circ 41822), Wu et al. (GCN Circ. 41824), and Li et al. (GCN Circ. 41825). Evans et al. (GCN Circ. 41831) report the discovery of an uncataloged X-ray source outside of the MXT error region. This source is close to a galaxy (object 121410150406866805 in the Pan-STARRS DR2 catalog) with r ≈ 19.6 and z ≈ 18.9. At this position in our difference image, we do not see an obvious optical transient, but our ability to quantify this is limited by significant subtraction artifacts. We thank the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir and the COLIBRÍ and DDRAGO engineering teams. COLIBRÍ is an astronomical observatory developed and operated jointly by France (AMU, CNES and CNRS) and Mexico (UNAM and SECIHTI). It is located at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, Mexico. View this GCN Circular online at https://gcn.nasa.gov/circulars/41832. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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

14 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41831 SUBJECT: GRB 250912A: Swift-XRT observations DATE: 25/09/14 14:45:17 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> P.A. Evans (U. Leicester), J.A. Kennea (PSU), E. Ambrosi (INAF-IASFPA) , A.P. Beardmore (U. Leicester), M.G. Bernardini (INAF-OAB), R. Brivio (INAF-OAB), D.N. Burrows (PSU), S. Campana (INAF-OAB), M. Capalbi (INAF-OAR), A. D'Ai (INAF-IASFPA), P. D'Avanzo (INAF-OAB), V. D'Elia (SSDC & INAF-OAR), S. Dichiara (PSU), M. Ferro (INAF-OAB), A. Melandri (INAF-OAR), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), M. Perri (SSDC & INAF-OAR), C. Salvaggio (INAF-OAB), T. Sbarrato (INAF-OAB), B. Sbarufatti (INAF-OAB), M.A. Williams (PSU) report on behalf of the Swift-XRT team: Swift-XRT has performed follow-up observations of the SVOM/ECLAIRs-detected source GRB 250912A (Ducoin et al., GCN 41820; Wang et al., GCN 41826; see also Fermi GBM team, GCN 41819), collecting 2.2 ks of Photon Counting (PC) mode data between T0+11 ks and T0+55 ks after the trigger. We have detected 1 source. This has been automatically classified as an uncatalogued X-ray source. Uncatalogued X-ray sources -------------------------- Source 1 (SWIFT J010009.7+111047): ================================== RA (J2000.0): 15.0405 = 01 00 09.72 Dec (J2000.0): +11.1797 = +11 10 46.9 Error: 7.3 (arcsec, radius, 90% confidence). Detect flag: GOOD Distance: 6.8 arcmin from the SVOM/ECLAIRs position. Mean rate: (3.6 [+2.0, -1.5])e-3 ct s^-1 Mean flux: (2.7 [+1.5, -1.1])e-13 erg cm^-2 s^-1 Peak rate: (3.6 [+2.0, -1.5])e-3 ct s^-1 Peak flux: (2.7 [+1.5, -1.1])e-13 erg cm^-2 s^-1 ECF: 7.43e-11 erg cm^-2 ct^-1 assuming NH=5.11e+20 cm^-2, gamma=0.69 determined from a spectral fit. RASS UL: 7.3e-02 ct s^-1 (converted to XRT; 0.3-10 keV) so the source is not above this 3-sigma upper limit. There is no evidence for fading. All fluxes are 0.3-10 keV, observed. For all flux conversions and comparisons with catalogues and upper limits from other missions, we assumed a power-law spectrum with NH=3x10^20 cm^-2 and photon index (Gamma)=1.7 unless otherwise stated. We note that source 1 lies outside the MXT error region reported by Ducoin et al. (GCN 41820), so it is likely unrelated with the GRB. The results of the XRT-team automatic analysis of the XRT observations, including a position-specific upper limit calculator, are available at https://www.swift.ac.uk/SVOM/SVOM_FIELD00037. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/41831. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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

14 Sep '25

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

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

14 Sep '25

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

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

14 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41828 SUBJECT: GRB 250912A: Fermi GBM Observation DATE: 25/09/14 00:30:11 GMT FROM: Jacob Smith at Fermi-GBM Team <jrs0118(a)uah.edu> Jacob Smith (UAH) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 21:06:23.64 UT on 12 September 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250912A (trigger 779403988/250912879), which was also detected by SVOM/ECLAIRs (Jean-Grégoire Ducoin et al. 2025, GCN 41820). The Fermi GBM on-ground location is consistent with the SVOM/ECLAIRs position. The angle from the Fermi LAT boresight is 49 degrees. The GBM light curve consists of multiple emission episodes with a duration (T90) of about 15 s (50-300 keV). The time-averaged spectrum from T0 to T0+15.6 s is best fit by a simple power law function with index -1.31 +/- 0.04. A power law function with an exponential high-energy cutoff fits the spectrum equally well with a with power law index = -1.05 +/- 0.12 and Epeak = 783 +/- 359. The event fluence (10-1000 keV) in this time interval is (3.1 +/- 0.1)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0-0.26 s in the 10-1000 keV band is 4 +/- 0.2 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog: https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html For Fermi GBM data and info, please visit the official Fermi GBM Support Page: https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/" View this GCN Circular online at https://gcn.nasa.gov/circulars/41828. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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