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[vsnet-grb-info 39907] EP250916a: Einstein Probe detection of an X-ray transient
by GCN Circulars 16 Sep '25

16 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41841 SUBJECT: EP250916a: Einstein Probe detection of an X-ray transient DATE: 25/09/16 16:02:54 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> Q. Y. Wu (NAO, CAS), C. Y. Dai (NJU), D. Y. Li, 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 through ground data analysis, designated EP250916a. The WXT position of the source is R.A. = 268.279 deg, DEC = -35.317 deg (J2000) with an uncertainty of 2.4 arcmin in radius (90% C.L. statistical and systematic), located at low Galactic latitude (l = 355.331, b = -4.634). The source was detected in three consecutive observations: the first started at 2025-09-16T03:33:13 (UTC) with a flux of ~3e-11 erg/s/cm^2; two subsequent observations, approximately 2 h and 6 h later, also detected the source with slightly higher fluxes of ~5e-11 erg/s/cm^2. As of the latest observation, the transient has persisted for ~7 hours. A preliminary spectral analysis shows that the 0.5-4 keV spectrum can be fitted by an absorbed power-law model with Galactic hydrogen column density fixed at 3.76 x 10^21 cm^-2 and a photon index of 1.1 (-/+0.8). No known X-ray sources have been found previously within the EP-WXT error circle. A stellar flare origin cannot be excluded at this stage. Follow-up observations with the Follow-up X-ray Telescope (FXT) on board EP have been scheduled, and further information will be updated when the telemetry data are 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/41841. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39906] Fermi GRB 250916A: Global MASTER-Net observations report
by GCN Circulars 16 Sep '25

16 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41840 SUBJECT: Fermi GRB 250916A: Global MASTER-Net observations report DATE: 25/09/16 15:30:58 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 250916A ( Fermi GBM team, GCN 41839) errorbox 2134 sec after notice time and 2165 sec after trigger time at 2025-09-16 14:05:26 UT, with upper limit up to 20.8 mag. The observations began at zenith distance = 44 deg. The sun altitude is -24.7 deg. The galactic latitude b = -20 deg., longitude l = 137 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2992979 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 2196 | 2025-09-16 14:05:26 | MASTER-Tunka | (01h 01m 35.41s , +42d 32m 50.5s) | C | 60 | 20.7 | 2196 | 2025-09-16 14:05:26 | MASTER- | (01h 02m 07.93s , +42d 25m 57.0s) | C | 60 | 20.5 | 2271 | 2025-09-16 14:06:42 | MASTER-Tunka | (01h 31m 07.38s , +48d 15m 08.4s) | C | 60 | 19.6 | 2271 | 2025-09-16 14:06:42 | MASTER- | (01h 31m 43.29s , +48d 08m 17.2s) | C | 60 | 19.5 | 2825 | 2025-09-16 14:15:56 | MASTER-Tunka | (01h 01m 37.13s , +42d 32m 44.7s) | C | 60 | 20.6 | 2825 | 2025-09-16 14:15:56 | MASTER- | (01h 02m 10.56s , +42d 25m 34.6s) | C | 60 | 20.6 | 2900 | 2025-09-16 14:17:11 | MASTER-Tunka | (01h 31m 06.83s , +48d 15m 06.1s) | C | 60 | 20.2 | 2900 | 2025-09-16 14:17:11 | MASTER- | (01h 31m 43.65s , +48d 07m 58.6s) | C | 60 | 19.8 | 4244 | 2025-09-16 14:39:34 | MASTER-Tunka | (01h 17m 38.67s , +38d 43m 55.2s) | C | 60 | 19.8 | 4244 | 2025-09-16 14:39:34 | MASTER- | (01h 18m 09.42s , +38d 37m 35.4s) | C | 60 | 19.7 | 4985 | 2025-09-16 14:51:56 | MASTER-Tunka | (01h 01m 35.37s , +42d 30m 26.2s) | C | 60 | 20.7 | 4985 | 2025-09-16 14:51:56 | MASTER- | (01h 02m 11.14s , +42d 22m 49.2s) | C | 60 | 20.6 | 5059 | 2025-09-16 14:53:10 | MASTER-Tunka | (01h 31m 07.69s , +48d 15m 07.8s) | C | 60 | 20.2 | 5059 | 2025-09-16 14:53:10 | MASTER- | (01h 31m 47.54s , +48d 07m 33.5s) | C | 60 | 19.9 | 5553 | 2025-09-16 15:01:23 | MASTER-Tunka | (01h 17m 43.01s , +38d 42m 15.8s) | C | 60 | 19.8 | 5553 | 2025-09-16 15:01:23 | MASTER- | (01h 18m 15.41s , +38d 35m 49.9s) | C | 60 | 19.7 | 5775 | 2025-09-16 15:05:05 | MASTER-Tunka | (01h 01m 31.47s , +42d 30m 13.1s) | C | 60 | 20.8 | 5775 | 2025-09-16 15:05:06 | MASTER- | (01h 02m 08.39s , +42d 23m 51.2s) | C | 60 | 20.6 | 5852 | 2025-09-16 15:06:22 | MASTER-Tunka | (01h 31m 05.98s , +48d 12m 03.1s) | C | 60 | 20.3 | 5852 | 2025-09-16 15:06:22 | MASTER- | (01h 31m 46.96s , +48d 05m 44.0s) | C | 60 | 19.9 | 6285 | 2025-09-16 15:13:36 | MASTER-Tunka | (01h 17m 33.49s , +38d 39m 54.6s) | C | 60 | 19.9 | 6285 | 2025-09-16 15:13:36 | MASTER- | (01h 18m 04.22s , +38d 34m 21.2s) | C | 60 | 19.7 | 6508 | 2025-09-16 15:17:18 | MASTER-Tunka | (01h 01m 28.89s , +42d 27m 40.0s) | C | 60 | 20.7 | 6508 | 2025-09-16 15:17:18 | MASTER- | (01h 02m 05.60s , +42d 21m 48.9s) | C | 60 | 20.7 | 6582 | 2025-09-16 15:18:33 | MASTER-Tunka | (01h 31m 05.87s , +48d 12m 44.6s) | C | 60 | 19.7 | 6582 | 2025-09-16 15:18:33 | MASTER- | (01h 31m 46.70s , +48d 06m 57.1s) | C | 60 | 19.6 | 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/41840. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39905] GRB 250916A: Fermi GBM Final Real-time Localization
by GCN Circulars 16 Sep '25

16 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41839 SUBJECT: GRB 250916A: Fermi GBM Final Real-time Localization DATE: 25/09/16 13:40:16 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 13:29:21 UT on 16 Sep 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250916A (trigger 779722166.007904 / 250916562). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 29.3, Dec = 40.3 (J2000 degrees, equivalent to J2000 01h 57m, 40d 17'), with a statistical uncertainty of 9.8 degrees. The angle from the Fermi LAT boresight is 66.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250916562/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250916562/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250916562/… View this GCN Circular online at https://gcn.nasa.gov/circulars/41839. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39904] EP250827b: VLA Observations
by GCN Circulars 16 Sep '25

16 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41838 SUBJECT: EP250827b: VLA Observations DATE: 25/09/16 13:27:15 GMT FROM: Genevieve Schroeder at Cornell University <genevieveschroeder(a)u.northwestern.edu> G. Schroeder (Cornell), D. A. Perley (LJMU), X. J. Hall (CMU), A. Y. Q. Ho (Cornell), Gokul Srinivasaragavan (UMD) report: We observed the location of the optical transient AT2025wkm, associated with EP250827b (Schroeder et al., GCN 41635) with the NSF’s Karl G. Jansky Very Large Array under program 25B-363 (PI Perley) on 2025 September 13 at a mid time of 13:02 UT (~17.3 days post discovery) at a mid frequency of 10 GHz (4 GHz bandwidth). Based on preliminary analysis, we detect a ~6 sigma source with a flux density of ~28 microJy. At a redshift of z = 0.120 (Sevilla et al., GCN 41639), this corresponds to a luminosity of ~1e28 erg/s/Hz. This is a factor of ~6 less luminous than the radio emission associated with SN1998bw (Kulkarni et al. Nature, 395, 663), and a factor of ~5 more luminous than the radio emission associated with SN2006aj (Soderberg et al. 2006, Nature, 442, 1014) at a similar observing frequency and epoch. If the radio emission can be attributed solely to star formation, this would indicate a radio star formation rate of ~3 Msol/year. Additional followup is planned to determine variability of the source. We thank the VLA staff for quickly approving and executing these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/41838. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[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 15 Sep '25

15 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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