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

[vsnet-grb-info 39366] GRB 250702B: Chandra X-ray Detection
by GCN Circulars 09 Aug '25

09 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41309 SUBJECT: GRB 250702B: Chandra X-ray Detection DATE: 25/08/09 23:30:50 GMT FROM: Brendan O'Connor at Carnegie Mellon University <boconno2(a)andrew.cmu.edu> B. O’Connor (CMU), D. Pasham (Eureka/George Washington), I. Andreoni (UNC), J. Hare (Catholic/GSFC), X. Hall (CMU), J. Carney (UNC), A. Palmese (CMU), M. Busmann (LMU), D. Gruen (LMU), report on behalf of a larger collaboration: We observed the position of the ultra-long X-ray and gamma-ray transient GRB 250702B (GCN #40883, #40886, #40890), also known as EP250702a (GCN #40906), with the Chandra X-ray Observatory (CXO) through Director's Discretionary Time (PI: O'Connor). Observations were carried out with ACIS-S starting on 2025-08-09 at 05:49:28 UT, corresponding to ~38 d after the initial Fermi trigger, for a total of 27.7 ks. We detect a clear X-ray source at the position of the infrared and radio counterparts of GRB 250702B (GCNs #40924, #41053). Adopting the best-fit spectrum from Swift/XRT (GCN #40919), we derive an unabsorbed 0.3-10 keV flux of ~3.3e-14 erg/cm^2/s. This is consistent with the extrapolation of the decay observed by Swift/XRT at earlier times (<10 days), and favors a powerlaw with temporal slope ~-1.9 as measured from the initial Fermi trigger time (GRB 250702D; GCN #40886). Further analysis is underway. We thank Pat Slane for approving our DDT request, and the entire staff of the Chandra X-ray Observatory for scheduling the observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/41309. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39365] EP250807a: Global MASTER-Net observations report
by GCN Circulars 09 Aug '25

09 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41308 SUBJECT: EP250807a: Global MASTER-Net observations report DATE: 25/08/09 21:49:54 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-Kislovodsk robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) was pointed to the EP250807a ( EP Team et al., GCN 41277) errorbox 36084 sec after notice time and 64631 sec after trigger time at 2025-08-08 17:30:13 UT, with upper limit up to 17.1 mag. Observations started at twilight. The observations began at zenith distance = 33 deg. The sun altitude is -11.5 deg. The galactic latitude b = 7 deg., longitude l = 45 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2963680 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 64661 | 2025-08-08 17:30:13 | MASTER-Kislovodsk | (18h 43m 28.97s , +14d 43m 36.5s) | C | 60 | 17.1 | 64831 | 2025-08-08 17:33:02 | MASTER-Kislovodsk | (18h 43m 28.20s , +14d 42m 55.0s) | C | 60 | 17.1 | 65007 | 2025-08-08 17:35:59 | MASTER-Kislovodsk | (18h 43m 24.84s , +14d 43m 09.9s) | C | 60 | 17.1 | 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/41308. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39364] Fermi GRB 250808A: Global MASTER-Net observations report
by GCN Circulars 09 Aug '25

09 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41307 SUBJECT: Fermi GRB 250808A: Global MASTER-Net observations report DATE: 25/08/09 21:48:36 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-Kislovodsk robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) started inspect of the Fermi GRB 250808A ( Fermi GBM team, GCN 41296) errorbox 18725 sec after notice time and 18749 sec after trigger time at 2025-08-08 23:37:41 UT, with upper limit up to 16.5 mag. The observations began at zenith distance = 79 deg. The sun altitude is -22.7 deg. The galactic latitude b = -42 deg., longitude l = 211 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2964051 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 18779 | 2025-08-08 23:37:41 | MASTER-Kislovodsk | (03h 36m 57.03s , -13d 48m 11.9s) | C | 60 | 15.0 | 20676 | 2025-08-09 00:09:18 | MASTER-Kislovodsk | (03h 54m 25.00s , -15d 41m 27.8s) | C | 60 | 12.1 | 21637 | 2025-08-09 00:25:19 | MASTER-Kislovodsk | (04h 11m 41.65s , -22d 41m 02.9s) | C | 60 | 15.0 | 21697 | 2025-08-09 00:25:19 | MASTER-Kislovodsk | (04h 11m 41.66s , -22d 41m 03.0s) | C | 180 | 15.9 | Coadd 21720 | 2025-08-09 00:26:42 | MASTER-Kislovodsk | (04h 11m 34.93s , -22d 42m 01.6s) | C | 60 | 15.3 | 21806 | 2025-08-09 00:28:08 | MASTER-Kislovodsk | (04h 11m 43.16s , -22d 41m 36.9s) | C | 60 | 15.7 | 21889 | 2025-08-09 00:29:31 | MASTER-Kislovodsk | (04h 11m 39.40s , -22d 40m 19.5s) | C | 60 | 15.8 | 21949 | 2025-08-09 00:29:31 | MASTER-Kislovodsk | (04h 11m 39.42s , -22d 40m 19.8s) | C | 180 | 16.4 | Coadd 21979 | 2025-08-09 00:31:01 | MASTER-Kislovodsk | (04h 11m 39.61s , -22d 41m 49.4s) | C | 60 | 15.8 | 22063 | 2025-08-09 00:32:25 | MASTER-Kislovodsk | (04h 11m 43.91s , -22d 40m 21.3s) | C | 60 | 15.7 | 22151 | 2025-08-09 00:33:53 | MASTER-Kislovodsk | (04h 11m 36.12s , -22d 40m 49.1s) | C | 60 | 15.9 | 22211 | 2025-08-09 00:33:53 | MASTER-Kislovodsk | (04h 11m 36.14s , -22d 40m 49.5s) | C | 180 | 16.5 | Coadd 22232 | 2025-08-09 00:35:14 | MASTER-Kislovodsk | (04h 11m 37.37s , -22d 39m 46.9s) | C | 60 | 15.9 | 22315 | 2025-08-09 00:36:37 | MASTER-Kislovodsk | (04h 11m 43.55s , -22d 40m 44.4s) | C | 60 | 15.8 | 22398 | 2025-08-09 00:38:00 | MASTER-Kislovodsk | (04h 11m 38.67s , -22d 41m 40.3s) | C | 60 | 16.0 | 22482 | 2025-08-09 00:39:24 | MASTER-Kislovodsk | (04h 11m 43.85s , -22d 41m 24.6s) | C | 60 | 15.9 | 22752 | 2025-08-09 00:43:54 | MASTER-Kislovodsk | (04h 11m 43.50s , -22d 39m 33.3s) | C | 60 | 15.7 | 22834 | 2025-08-09 00:45:16 | MASTER-Kislovodsk | (04h 11m 39.63s , -22d 40m 21.8s) | C | 60 | 15.7 | 22894 | 2025-08-09 00:45:16 | MASTER-Kislovodsk | (04h 11m 39.63s , -22d 40m 21.9s) | C | 180 | 16.1 | Coadd 22919 | 2025-08-09 00:46:41 | MASTER-Kislovodsk | (04h 11m 37.85s , -22d 39m 18.0s) | C | 60 | 15.7 | 23011 | 2025-08-09 00:48:13 | MASTER-Kislovodsk | (04h 11m 44.98s , -22d 40m 14.4s) | C | 60 | 15.2 | 23093 | 2025-08-09 00:49:35 | MASTER-Kislovodsk | (04h 11m 39.09s , -22d 41m 10.2s) | C | 60 | 15.0 | 23153 | 2025-08-09 00:49:35 | MASTER-Kislovodsk | (04h 11m 39.09s , -22d 41m 10.2s) | C | 180 | 15.9 | Coadd 23199 | 2025-08-09 00:51:21 | MASTER-Kislovodsk | (04h 11m 44.24s , -22d 40m 39.2s) | C | 60 | 15.4 | 23283 | 2025-08-09 00:52:45 | MASTER-Kislovodsk | (04h 11m 42.44s , -22d 39m 17.6s) | C | 60 | 15.4 | 23381 | 2025-08-09 00:54:23 | MASTER-Kislovodsk | (04h 11m 42.54s , -22d 40m 34.8s) | C | 60 | 15.0 | 23467 | 2025-08-09 00:55:49 | MASTER-Kislovodsk | (04h 11m 45.72s , -22d 38m 58.4s) | C | 60 | 14.3 | 24214 | 2025-08-09 01:08:16 | MASTER-Kislovodsk | (04h 11m 48.73s , -22d 39m 27.6s) | C | 60 | 13.7 | 24300 | 2025-08-09 01:09:42 | MASTER-Kislovodsk | (03h 36m 57.33s , -13d 44m 50.9s) | C | 60 | 12.9 | 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/41307. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39363] Fermi Gamma-ray Burst Monitor trigger 776449964/250809689 is not a GRB
by GCN Circulars 09 Aug '25

09 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41306 SUBJECT: Fermi Gamma-ray Burst Monitor trigger 776449964/250809689 is not a GRB DATE: 25/08/09 21:46:54 GMT FROM: Bagrat Mailyan at Florida Tech <mbagrat(a)gmail.com> B. Mailyan (Florida Tech) reports on behalf of the Fermi Gamma-ray Burst Monitor Team: "The Fermi Gamma-ray Burst Monitor (GBM) trigger 776449964/250809689 at 16:32:39.78 UT on 09 August 2025, tentatively classified as a GRB, is in fact not due to a GRB. This trigger is likely due to particle activity." View this GCN Circular online at https://gcn.nasa.gov/circulars/41306. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39362] GRB 250808A: VLT X-shooter candidate counterpart
by GCN Circulars 09 Aug '25

09 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41305 SUBJECT: GRB 250808A: VLT X-shooter candidate counterpart DATE: 25/08/09 21:27:38 GMT FROM: luca.izzo(a)inaf.it A. Levan (Radboud U.), D. B. Malesani (DAWN/NBI and Radboud Univ.), I. F. Giudice (INAF/OACn), L. Izzo (INAF/OACn & DARK/NBI), A. L. Thakur (INAF-IAPS), N. R. Tanvir (U. Leicester), G. Corcoran (UCD), A. de Ugarte Postigo (LAM), A. Martin-Carrillo (UCD), A. Saccardi (CEA/Irfu), M. De Pasquale (U. Messina), D. Hartmann (Clemson U.) report on behalf of the Stargate collaboration: We observed the field of SVOM/ECLAIRs GRB 250808A (Adrien et al., GCN 41297) using ESO VLT UT3 (Melipal) equipped with the X-shooter instrument, starting at 9 August 08:56 UT, approximately 14.5 hr after the burst trigger. A sequence of 1x120s (r band) and 5x60s (z band) images was obtained with the acquisition camera. Comparison to z-band images obtained with the Legacy Survey shows a new source within the Swift/XRT localisation region (Evans et al., GCN 41300) at coordinates: RA(J2000) = 04:14:12.39 Dec(J2000) = -22:49:23.5 The source has an approximate magnitude of z ~ 21.8 mag (AB). We suggest this is the optical counterpart of GRB 250808A. We notice that this source is also detected in the r-band acquisition image. We also note the presence of a very faint (r = 24.28 mag, z = 23.73 mag) catalogued object in the Legacy Survey DR10 just below the afterglow position. We propose this source to be the host galaxy of GRB 250808A. We acknowledge excellent support from the ESO observing staff in Paranal, in particular Cecilia Bustos, Rodrigo Palominos, and Rob van Holstein. View this GCN Circular online at https://gcn.nasa.gov/circulars/41305. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39361] GRB 250809A: Prompt enhanced Swift-XRT position
by GCN Circulars 09 Aug '25

09 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41304 SUBJECT: GRB 250809A: Prompt enhanced Swift-XRT position DATE: 25/08/09 17:25:56 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team: Using 923 s of promptly downlinked XRT event data for GRB 250809A, we find an enhanced XRT position of the afterglow: RA, Dec: 233.00043, -53.29626 which is equivalent to: RA (J2000) = 15 32 00.10 Dec (J2000) = -53 17 46.5 with an uncertainty of 3.0 arcseconds (radius, 90% confidence). Analysis of the promptly available data is online at http://www.swift.ac.uk/sper/1340954. Position enhancement is described by Goad et al. (2007, A&A, 476, 1401) and Evans et al. (2009, MNRAS, 397, 1177). This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/41304. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39360] GRB 250809A: Swift detection of a gamma ray burst
by GCN Circulars 09 Aug '25

09 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41303 SUBJECT: GRB 250809A: Swift detection of a gamma ray burst DATE: 25/08/09 17:09:11 GMT FROM: David Palmer at LANL <palmer(a)lanl.gov> T. M. Parsotan (GSFC), R. Brivio (INAF-OAB), J. J. DeLaunay (PSU), S. Dichiara (PSU), R. Gupta (NASA GSFC) and D. M. Palmer (LANL) report on behalf of the Neil Gehrels Swift Observatory Team: At 16:53:19 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 250809A (trigger=1340954). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 233.015, -53.289 which is RA(J2000) = 15h 32m 04s Dec(J2000) = -53d 17' 18" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a complex structure with a duration of about 40 sec. The peak count rate was ~1000 counts/sec (15-350 keV), at ~11 sec after the trigger. The XRT began observing the field at 16:55:25.0 UT, 125.5 seconds after the BAT trigger. Using promptly downlinked data we find a bright, uncatalogued X-ray source located at RA, Dec 233.00282, -53.29640 which is equivalent to: RA(J2000) = 15h 32m 00.68s Dec(J2000) = -53d 17' 47.0" with an uncertainty of 4.3 arcseconds (radius, 90% containment). This location is 37 arcseconds from the BAT onboard position, within the BAT error circle. This position may be improved as more data are received; the latest position is available at https://www.swift.ac.uk/sper. We cannot determine whether the source is fading at the present time. A power-law fit to a spectrum formed from promptly downlinked event data gives a column density consistent with the Galactic value of 8.04 x 10^21 cm^-2 (Willingale et al. 2013). The initial flux in the 2.5 s image was 5.16e-10 erg cm^-2 s^-1 (0.2-10 keV). UVOT took a finding chart exposure of 250 seconds with the U filter starting 128 seconds after the BAT trigger. No credible afterglow candidate has been found in the initial data products. The 2.7'x2.7' sub-image covers 100% of the XRT error circle. Because of the density of catalogued stars, further analysis is required to report an upper limit for any afterglow in the sub-image. The 8'x8' region for the list of sources generated on-board covers 100% of the XRT error circle. Because of the density of catalogued stars, further analysis is required to report an upper limit for any afterglow in the region. No correction has been made for the large, but uncertain, extinction expected. Burst Advocate for this burst is T. M. Parsotan (tyler.parsotan AT nasa.gov). Please contact the BA by email if you require additional information regarding Swift followup of this burst. In extremely urgent cases, after trying the Burst Advocate, you can contact the Swift PI by phone (see Swift TOO web site for information: http://www.swift.psu.edu/) View this GCN Circular online at https://gcn.nasa.gov/circulars/41303. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39359] GRB 250808A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
by GCN Circulars 09 Aug '25

09 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41302 SUBJECT: GRB 250808A: SVOM/COLIBRÍ (FM-GFT) optical upper limit DATE: 25/08/09 17:04:52 GMT FROM: Antonio de Ugarte Postigo at LAM, CNRS <adeugartepostigo(a)gmail.com> Antonio de Ugarte Postigo (LAM), Noémie Globus (UNAM), Jean-Grégoire Ducoin (CPPM), Alan M. Watson (UNAM), Jean-Luc Atteia (IRAP), Rosa L. Becerra (U Roma), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Fredd Alvarez (UNAM), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (OCA), Nathaniel R. Butler (ASU) , Damien Dornic (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Benjamin Schneider (LAM), D. Adrien (CEA) and D. Turpin (CEA): We imaged the field of the SVOM GRB 250808A (Adrien et al., GCN Circ. 41297) using the DDRAGO wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope. We observed from 2025-08-09 11:11 to 11:50 UTC (from 16.8 to 17.4 hours after the trigger) and obtained 32x60 s of exposure in the i filter. The observations were carried out mostly during the astronomical twilight and with an average airmass ~ 2.7. The data were reduced and coadded with the COLIBRÍ pipeline and analysed 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. Within the full SVOM/ECLAIRs error circle we do not detect any new source down to a 5-sigma limiting magnitude of i > 21.4 mag. More specifically, within the error circle of the XRT afterglow (Evans et al. GCN Circ. 41300) we do not detect any significant optical counterpart down to the following 3-sigma limit: i > 22.0 mag 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/41302. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39358] GRB 250808A: Fermi GBM Observation
by GCN Circulars 09 Aug '25

09 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41301 SUBJECT: GRB 250808A: Fermi GBM Observation DATE: 25/08/09 12:34:41 GMT FROM: A. Holzmann Airasca at University of Trento and INFN Bari <a.holzmannairasca(a)unitn.it> A. Holzmann Airasca (UniTrento and INFN Bari), S. Bala (USRA) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 18:25:12.48 UT on 08 August 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250808A (trigger 776370317/250808768). which was also detected by SVOM/ECLAIRs (D. Adrien et al. 2025, GCN 41297). The Fermi GBM on-ground location is consistent with the SVOM/ECLAIRs position. The angle from the Fermi LAT boresight is 33 degrees. The GBM light curve consists of a single variable emission episode with a duration (T90) of about 49 s (50-300 keV). The time-averaged spectrum from T0-6.1 to T0+51.2 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -1.1 +/- 0.2 and the cutoff energy, parameterized as Epeak, is 70 +/- 7 keV. The event fluence (10-1000 keV) in this time interval is (2.7 +/- 0.2)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0+45 s in the 10-1000 keV band is 2.5 +/- 0.2 ph/s/cm^2. A Band function fits the spectrum equally well with Epeak= 55 +/- 9 keV, alpha = -0.7 +/- 0.3 and beta = -2.5 +/- 0.3. 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/41301. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39357] GRB 250808A: Swift-XRT candidate counterpart detection
by GCN Circulars 09 Aug '25

09 Aug '25

TITLE: GCN CIRCULAR NUMBER: 41300 SUBJECT: GRB 250808A: Swift-XRT candidate counterpart detection DATE: 25/08/09 09:08:58 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 250808A, collecting 1.7 ks of Photon Counting (PC) mode data between T0+3.7 ks and T0+5.6 ks after the trigger. A candidate counterpart has been found. The details of this source are: Source 1 (SWIFT J041412.2-224923): ================================== RA (J2000.0): 63.5510 = 04h 14m 12.24s Dec (J2000.0): -22.8231 = -22d 49' 23.2" Error: 3.9 (arcsec, radius, 90% confidence). Detect flag: GOOD Distance: 4.9 arcmin from the SVOM/ECLAIRs position. Mean rate: 0.140 +/- 0.013 ct s^-1 Mean flux: (4.58 +/- 0.43)e-12 erg cm^-2 s^-1 Peak rate: 0.204 +/- 0.046 ct s^-1 Peak flux: (6.7 +/- 1.5)e-12 erg cm^-2 s^-1 ECF: 3.27e-11 erg cm^-2 ct^-1 assuming NH=1.35e+21 cm^-2, gamma=2.07 determined from a spectral fit. XMM UL: 2.2e-12 erg cm^-2 s^-1, (0.3-10 keV) so the source is 3.0-sigma above this 3-sigma upper limit. The source may be fading, at the 2.1-sigma level. 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. 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_FIELD00027. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/41300. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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