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

[vsnet-grb-info 40033] GRB 250922B: SVOM/GRM observation
by GCN Circulars 24 Sep '25

24 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41966 SUBJECT: GRB 250922B: SVOM/GRM observation DATE: 25/09/24 14:10:14 GMT FROM: Chenwei Wang at IHEP <cwwang(a)ihep.ac.cn> SVOM/GRM team: Chen-Wei Wang. Wen-Jun Tan, Yue Huang, Shi-Jie Zheng, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Stéphane Schanne (CEA) Report on behalf of the SVOM team: SVOM/GRM was triggered on-ground by a burst GRB 250922B at 2025-09-22T21:13:25.900 UTC (T0), which is also detected by Fermi/GBM (Fermi GBM Team, GCN#41944). With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of a single pulse with a T90 of 0.07 +0.05/-0.03 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb250922B.png In addition, the position of this burst, as determined by Fermi/GBM (RA= 48.7, DEC= 30.7, GCN#41944), is located at about 52 degrees from the SVOM optical axis, which is just outside the ECLAIRs field of view. With this localization, the time-averaged spectrum from T0-0.2 to T0+0.1 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.15 +0.12/-0.15 and the cutoff energy, parameterized as Epeak, is 1060 +110/-460 keV. The event fluence (10-1000 keV) in this time interval is (4.38 +0.55/-0.53)E-07 erg/cm^2. The 'Amati' relation of GRB 250922B is shown at: https://www.bursthub.cn//admin/static/svgrb250922B_amati.png 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. GRM is developed by the Institute of High Energy Physics (IHEP) of CAS. The SVOM point of contact for this burst is: Chen-Wei Wang (IHEP)(cwwang(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/41966. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40032] GRB 250920C: TRT optical observation
by GCN Circulars 24 Sep '25

24 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41965 SUBJECT: GRB 250920C: TRT optical observation DATE: 25/09/24 13:37:17 GMT FROM: Zipei Zhu at NAOC <zpzhu(a)nao.cas.cn> Z.P. Zhu (NAOC), K. Noysena, K. Chanchaiworawit, S. Tinyanont (NARIT), S.Y. Fu (HUST), L.B. He, X. Liu, J. An, S.Q. Jiang, D. Xu (NAOC) report on behalf of a large collaboration: We observed the field of GRB 250920C (Fermi GBM team, GCN 41903; Gupta et al., GCN 41904; Mailyan & Meegan, GCN 41917; Gupta et al., GCN 41924; Wang et al., GCN 41929; Panteleeva et al., GCN 41957 ), using the 0.7-m telescope of the Thai Robotic Telescope network (TRT), located at New South Wales, Australia (SBO). Observations started at 18:21:14 UTC on 2025-09-20, i.e., ~ 2.9 hours after the Swift/BAT trigger and a series of frames in the R band were obtained. The optical afterglow (Wortley et al., GCN 41907; Strausbaugh et al., GCN 41911; Ghosh et al., GCN 41913; Kuin et al., GCN 41920; Mohan et al., GCN 41925; Sanchez-Ramirez et al., GCN 41928; Guiffreda et al., GCN 41943; de Ugarte Postigo et al., GCN 41951; de Wet et al., GCN 41952; Izzo et al., GCN 41955; Zheng & Filippenko, GCN 41956; ) was clearly detected in our stacked R-band frame with a brightness of 18.87 +/- 0.02, calibrated with Pan-STARRS DR2 catalog and not corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/41965. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40031] GRB 250924B: Fermi GBM Final Localization
by GCN Circulars 24 Sep '25

24 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41964 SUBJECT: GRB 250924B: Fermi GBM Final Localization DATE: 25/09/24 13:25:19 GMT FROM: Padraig McDermott at University College Dublin <padraig.mcdermott(a)ucdconnect.ie> The Fermi GBM team reports the detection of a likely SHORT GRB "At 10:26:58.90 UT on 24 September 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB250924B (trigger 780402423/250924435). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 306.44, Dec = -61.82 (J2000 degrees, equivalent to J2000 20h 25m, -61d 49'), with a statistical uncertainty of 9.50 degrees. The angle from the Fermi LAT boresight is 150 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250924435/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250924435/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250924435/…" View this GCN Circular online at https://gcn.nasa.gov/circulars/41964. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40030] GRB 250924A: COLIBRÍ optical observations
by GCN Circulars 24 Sep '25

24 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41963 SUBJECT: GRB 250924A: COLIBRÍ optical observations DATE: 25/09/24 12:35:04 GMT FROM: Benjamin Schneider at MIT <bschn(a)mit.edu> Benjamin Schneider (LAM), Camila Angulo (UNAM), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Rosa L. Becerra (U Roma), Antonio de Ugarte Postigo (LAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Fredd Alvarez (UNAM), Jean-Luc Atteia (IRAP), Dalya Akl (NYUAD), Sarah Antier (OCA), Nathaniel R. Butler (ASU), 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) and Ny Avo Rakotondrainibe (LAM): We imaged the field of the Swift GRB 250924A (Siegel et al., GCN Circ. 41959) using the DDRAGO wide-field imager on the COLIBRÍ telescope. We observed from 2025-09-24 08:33:51 to 09:46:24 UTC (from 15 to 88 minutes after the trigger) and obtained images in the g, r, i, z and y filters. 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. We detect the optical counterpart reported by source Siegel et al., GCN Circ. 41959 and Becerra et al., GCN Circ. 41960 at: RA(J2000) = 3:27:29.71 = 51.8738 degrees Dec(J2000) = +74:39:33.7 = +74.6594 degrees with an uncertainty of 0.5 arcsec. The preliminary magnitudes derived for that source are: Start (UT) | mid T0+T (s) | Band | Exp | Mag | Error --------------------|---------------|------|------|------|------ 2025-09-24T09:01:29 | 2853 | g | 3x60 | 20.12 | 0.05 2025-09-24T08:33:51 | 1054 | r | 3x60 | 18.90 | 0.04 2025-09-24T09:03:50 | 2994 | i | 3x60 | 19.38 | 0.05 2025-09-24T08:33:51 | 1054 | z | 3x60 | 18.39 | 0.05 2025-09-24T09:02:40 | 3963 | y | 16x60 | 19.26 | 0.06 From subsequent r-band images obtained between 0.26 and 2.21 hr after the burst, we measure a temporal decay slope of alpha = 0.6 +/- 0.1. Further observations are ongoing. 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/41963. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40029] Swift GRB 250924A: Global MASTER-Net observations report
by GCN Circulars 24 Sep '25

24 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41962 SUBJECT: Swift GRB 250924A: Global MASTER-Net observations report DATE: 25/09/24 12:04:41 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) was pointed to the Swift GRB 250924A ( M. H. Siegel et al., GCN 41959) errorbox 13196 sec after notice time and 13280 sec after trigger time at 2025-09-24 11:59:49 UT, with upper limit up to 16.2 mag. Observations started at twilight. The observations began at zenith distance = 49 deg. The sun altitude is -10.0 deg. The galactic latitude b = 15 deg., longitude l = 133 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2998975 We obtain a following upper limits. Tmid-T0 | Site |Filt.| Expt. | Limit| Comment _________|_____________________|_____|_______|______|________ 13310 | MASTER-Tunka | C | 60 | 16.2 | 13310 | MASTER- | C | 60 | 16.2 | Coadd 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/41962. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40028] GRB 250919A / EP250919a: further LCO optical observation
by GCN Circulars 24 Sep '25

24 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41961 SUBJECT: GRB 250919A / EP250919a: further LCO optical observation DATE: 25/09/24 11:30:34 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> D. Turpin (CEA/Irfu), A. Saccardi (CEA/Irfu), J. T. Palmerio (CEA/Irfu), Z. Q. Wang (GXU), Y. F. Liang (PMO), report on behalf of the SVOM mission team: We re-observed the field of GRB 250919A / EP250919a (Fermi GBM Team, GCN 41874; Liang et al., GCN 41879; Wang et al., GCN 41882; Holzmann Airasca et al., GCN 41884; Waratkar et al., GCN 41888; Cheung et al., GCN 41891; Wang et al. GCN 41900; Frederiks et al. GCN 41905) with the LCO 1m telescope at Siding Spring Observatory equipped with the Sinistro instrument. We obtained 3x200 s exposures in the SDSS r filter. The optical counterpart (Li et al., GCN 41877; Levan et al., GCN 41883; Oates et al., GCN 41886; Lipunov et al., GCN 41893; Ma et al. GCN 41894, Saccardi et al., GCN 41906) is still clearly detected in our subtracted image (using the Legacy Survey DR10 image template) with the following magnitude (calibrated against the SkyMApper DR4 catalogued stars, not corrected for Galactic extinction): r = 20.67 +/- 0.08 (AB), at a mid-time of 4.47 days after the trigger. Compared to our first epoch (Saccardi et al., GCN 41906), the afterglow is fading as a power law decay with alpha ~ 1.1 with no evidence of any late break so far. Further observations are planned. This project is funded by the SVOM collaboration. View this GCN Circular online at https://gcn.nasa.gov/circulars/41961. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40027] GRB 250924A: DDOTI Detection of the Optical Counterpart
by GCN Circulars 24 Sep '25

24 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41960 SUBJECT: GRB 250924A: DDOTI Detection of the Optical Counterpart DATE: 25/09/24 09:00:57 GMT FROM: Rosa L. Becerra at Tor Vergata, Roma <rosa.becerra(a)roma2.infn.it> Rosa L. Becerra (U Roma), Sahil Atri (U Roma), Alan M. Watson (UNAM), Camila Angulo Valdez (UNAM), Nat Butler (ASU), Simone Dichiara (Penn State University), Tsvetelina Dimitrova (ASU), Alexander Kutyrev (GSFC/UMD), William H. Lee (UNAM), Océlotl López (UNAM), Margarita Pereyra (UNAM) and Eleonora Troja (U Roma) report: We observed the field of GRB 250924A detected by Swift (Siegel et al., GCN Circ. 41959) with the DDOTI/OAN wide-field imager at the Observatorio Astronómico Nacional on Sierra San Pedro Mártir (http://ddoti.astroscu.unam.mx) on the night of 2025-09-24 UTC. DDOTI observed the Swift/UVOT position (Siegel et al., GCN Circ. 41959) from 08:35 UTC to 08:40 UTC (from T+17.3 to T+ 22.1 min after the trigger), obtaining a total exposure of 4 minutes. By comparing our observations with the USNO-B1 and Pan-STARRS PS1 DR2 catalogs, we detect an uncatalogued source with a preliminary AB magnitude of: w = 19.47 +/- 0.05. We thank the staff of the Observatorio Astronómico Nacional on the Sierra of San Pedro Mártir. View this GCN Circular online at https://gcn.nasa.gov/circulars/41960. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40026] GRB 250924A: Swift detection of a burst with an optical counterpart
by GCN Circulars 24 Sep '25

24 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41959 SUBJECT: GRB 250924A: Swift detection of a burst with an optical counterpart DATE: 25/09/24 08:35:33 GMT FROM: K.L. Page at U Leicester <klp5(a)leicester.ac.uk> M. H. Siegel (PSU), J. J. DeLaunay (PSU), R. Gupta (NASA GSFC), S. Lanava (PSU), K. L. Page (U Leicester) and D. M. Palmer (LANL) report on behalf of the Neil Gehrels Swift Observatory Team: At 08:18:29 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 250924A (trigger=1351790). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 51.865, +74.652 which is RA(J2000) = 03h 27m 28s Dec(J2000) = +74d 39' 07" 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 30 sec. The peak count rate was ~1000 counts/sec (15-350 keV), at ~17 sec after the trigger. The XRT began observing the field at 08:21:32.8 UT, 183.6 seconds after the BAT trigger. Using promptly downlinked data we find a bright, fading, uncatalogued X-ray source with an enhanced position: RA, Dec 51.87141, 74.65894 which is equivalent to: RA(J2000) = 03h 27m 29.14s Dec(J2000) = +74d 39' 32.2" with an uncertainty of 2.7 arcseconds (radius, 90% containment). This location is 25 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. A power-law fit to a spectrum formed from promptly downlinked event data gives a column density consistent with the Galactic value of 2.77 x 10^21 cm^-2 (Willingale et al. 2013). The initial flux in the 2.5 s image was 1.03e-09 erg cm^-2 s^-1 (0.2-10 keV). UVOT took a finding chart exposure of 150 seconds with the White filter starting 192 seconds after the BAT trigger. There is a candidate afterglow in the rapidly available 2.7'x2.7' sub-image at RA(J2000) = 03:27:29.62 = 51.87340 DEC(J2000) = +74:39:34.0 = 74.65945 with a 90%-confidence error radius of about 0.62 arc sec. This position is 1.6 arc sec. from the center of the XRT error circle. The estimated magnitude is 17.74 with a 1-sigma error of about 0.14. No correction has been made for the expected extinction corresponding to E(B-V) of 0.316. Burst Advocate for this burst is M. H. Siegel (siegel AT swift.psu.edu) 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/41959. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40025] GRB 250920B: AbAO optical upper limits
by GCN Circulars 23 Sep '25

23 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41958 SUBJECT: GRB 250920B: AbAO optical upper limits DATE: 25/09/23 21:32:13 GMT FROM: Nicolai Pankov at HSE, IKI RAS <colinsergesen(a)gmail.com> N. Pankov (HSE, IKI), A. Pozanenko (IKI), A. Moskvitin (SAO RAS), R. Ya. Inasaridze (AbAO) report on behalf of GRB-IKI-FuN: We observed the field of a long GRB 250920B detected by Fermi/GBM (The Fermi GBM team GCN 41897), Swift (Gupta et. al, GCN 41898), with the AS-32 0.7m telescope of AbAO. We obtained two series of images in the R band on epochs 2025-09-22 and 2025-09-23 (~2.3 and ~3.3 days since trigger, respectively). The optical afterglow initially detected by Swift/UVOT (Gupta et. al, GCN 41898) and further observed by (WU et. al, GCN 41908; Hall et. al, GCN 41914; Pankov et. al, GCN 41931; Reguitti et. al, GCN 41932; Moskvitin et. al, GCN 41948; Pankov et. al, GCN 41953) is not detected in the stacked images of both epochs. Preliminary upper limits are as follows: Date UTstart Exptime t-T0 Filter OT Err. UL (nxs) (mid, days) (3sigma) 2025-09-22 16:09:15 20x2+97x30 2.32458 R n/d n/d 20.3 2025-09-23 16:04:34 153*30 3.33076 R n/d n/d 20.3 The photometry was calibrated against nearby PS1 DR2 stars (R-mags obtained via Lupton 2005 transformations) and not corrected for the Galactic extinction. Ref. stars PS1 DR2 (Lupton 2005) RA Dec R R_err 187.24325 47.82521 15.134 0.007 187.41433 47.78151 14.974 0.008 View this GCN Circular online at https://gcn.nasa.gov/circulars/41958. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40024] Konus-Wind detection of GRB 250920C
by GCN Circulars 23 Sep '25

23 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41957 SUBJECT: Konus-Wind detection of GRB 250920C DATE: 25/09/23 19:12:38 GMT FROM: Valentina Panteleeva at Ioffe Institute <panteleevav228(a)gmail.com> V. Panteleeva, D. Frederiks, A. Lysenko, A. Ridnaia, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report: The long-duration GRB 250920C (Fermi-GBM detection: The Fermi GBM team, GCN 41903; Mailyan & Meegan, GCN 41917; Swift-BAT detection: Gupta et al., GCN 41904; Gupta et al., GCN 41924; SVOM-GRM observaion: Wang et al., GCN 41929) triggered Konus-Wind at T0=55519.312 s UT (15:25:19.312). The burst light curve shows a multipeaked structure which starts at ~T0-0.4 s and has a total duration of ~41 s. The emission is seen up to ~2 MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB250920_T55519/ As observed by Konus-Wind, the burst had the total fluence of 2.91(-0.21,+0.29)x10^-5 erg/cm2, and the 64-ms peak flux, measured from T0+25.904 s, of 8.27(-0.78,+0.78)x10^-6 erg/cm2/s (both in the 20 keV - 10 MeV energy range). The time-averaged spectrum of the burst (measured from T0 to T0+41.216 s) is best fit in the 20 keV - 10 MeV range by the GRB (Band) model with the following parameters: the low-energy photon index alpha = -1.22(-0.07,+0.09), the high energy photon index beta = -3.19(-6.81,+0.51), the peak energy Ep = 160(-12,+9) keV (chi2 = 104/97 dof). The spectrum near the maximum count rate (measured from T0+24.832 to T0+33.024 s) is best fit in the 20 keV - 10 MeV range by a power law with exponential cutoff model: dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) with alpha = -1.14(-0.07,+0.07) and Ep = 220(-14,+16) keV (chi2 = 96/81 dof). Fitting by a GRB (Band) model yields the same alpha and Ep, and an upper limit on the high energy photon index: beta < -3.15 (chi2 = 97/80 dof). Assuming the redshift z=1.399 (Sanchez-Ramirez et al., GCN 41928; Izzo et al., GCN 41955) and a standard cosmology with H_0 = 67.3 km/s/Mpc, Omega_M = 0.315, and Omega_Lambda = 0.685 (Planck Collaboration, 2014), we estimate the following rest-frame parameters: the isotropic energy release E_iso is 1.54(-0.11,+0.16)x10^53 erg, the peak luminosity L_iso is 1.05(-0.10,+0.10)x10^53 erg/s, the rest-frame peak energy of the time-averaged spectrum Ep,i,z is 383(-30,+22) keV and the spectrum near the maximum count rate Ep,p,z is 528(-33,+38) keV. With the obtained estimates, GRB 250920C is inside 68% prediction bands for both the 'Amati' and the 'Yonetoku' relations derived for the sample of >300 long KW GRBs with known redshifts (Tsvetkova et al., 2017; Tsvetkova et al., 2021), see http://www.ioffe.ru/LEA/GRBs/GRB250920_T55519/GRB250920C_rest_frame.pdf All the quoted errors are at the 68% confidence level. All the quoted values are preliminary. View this GCN Circular online at https://gcn.nasa.gov/circulars/41957. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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