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[vsnet-grb-info 39967] Swift GRB 250920B: Global MASTER-Net observations report
by GCN Circulars 20 Sep '25

20 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41901 SUBJECT: Swift GRB 250920B: Global MASTER-Net observations report DATE: 25/09/20 13:28:21 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 250920B ( R. Gupta et al., GCN 41898) errorbox 16004 sec after notice time and 16025 sec after trigger time at 2025-09-20 13:13:36 UT, with upper limit up to 19.9 mag. The observations began at zenith distance = 66 deg. The sun altitude is -19.4 deg. The galactic latitude b = 69 deg., longitude l = 132 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2995928 We obtain a following upper limits. Tmid-T0 | Site |Filt.| Expt. | Limit| Comment _________|_____________________|_____|_______|______|________ 16056 | MASTER-Tunka | C | 60 | 19.9 | 16056 | MASTER- | 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/41901. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39966] GRB 250919A / EP250919a: Insight-HXMT detection
by GCN Circulars 20 Sep '25

20 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41900 SUBJECT: GRB 250919A / EP250919a: Insight-HXMT detection DATE: 25/09/20 13:01:19 GMT FROM: Chenwei Wang at IHEP <cwwang(a)ihep.ac.cn> Chen-Wei Wang, Shao-Lin Xiong, Shi-Jie Zheng, and Chao Zheng report on behalf of the Insight-HXMT team: At 2025-09-19T00:29:15.000 (T0), Insight-HXMT/HE detected the burst GRB 250919A, which is also detected by Fermi/GBM (Fermi GBM Team, GCN#41874), SVOM/GRM (Wang et al., GCN#41882), Fermi/LAT (A. Holzmann Airasca, GCN#41884), NuSTAR (G. Waratkar et al., GCN#41888), Glowbug (C.C. Cheung et al., GCN#41891), associated with EP250919a detected by EP/WXT (Liang et al., GCN Circ. 41879). The Insight-HXMT/HE light curve mainly consists of multi-pulses with a T90 of 117.0 +4.5/-3.0 s. The 1s peak rate, measured from T0+10.250 s, is 14624 cnts/sec. The total counts from this burst is 98750 counts. However, the HE detector was suffered from saturation from T0+6 s to T0+8 s and T0+10 s to T0+11 s due to the high-brightness. The HXMT/HE light curve can be found here: https://www.bursthub.cn//admin/static/hxmtgrb250919A.png All measurements above are made with the CsI detectors operating in the regular mode with the energy range of about 60-900 keV (deposited energy). Only gamma-rays with energy greater than about 200 keV can penetrate the spacecraft and leave signals in the CsI detectors installed inside of the telescope. Insight-HXMT is the first Chinese space X-ray telescope, which was funded jointly by the China National Space Administration (CNSA) and the Chinese Academy of Sciences (CAS). More information about it could be found at: http://www.hxmt.org. View this GCN Circular online at https://gcn.nasa.gov/circulars/41900. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39965] GRB 250920A: AstroSat CZTI detection
by GCN Circulars 20 Sep '25

20 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41899 SUBJECT: GRB 250920A: AstroSat CZTI detection DATE: 25/09/20 09:29:54 GMT FROM: Anuraag Arya at IIT Bombay <aryaanuraag910(a)gmail.com> Harsha K. H. (IUCAA), S. Salunke (IUCAA), M. Tembhurnikar (IUCAA), A. Goyal (IITB), A. Arya (IITB), U. Pathak(IITB), G. Waratkar (Caltech/IITB), A. Vibhute (IUCAA), V. Bhalerao (IITB), D. Bhattacharya (Ashoka University/IUCAA), A. R. Rao (IUCAA/TIFR), and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration: Analysis of AstroSat CZTI data with the CIFT framework (Sharma et al., 2021, JApA, 42, 73) showed the detection of a bright, long GRB 250920A which was also detected by Fermi GBM (Fermi GBM Team, GCN Circ. 41895). The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2025-09-20 02:54:08.95 UTC. The measured peak count rate associated with the burst is 636 (+45, -50) counts/s above the background in the combined data of two quadrants (out of four), with a total of 1944 (+129, -140) counts. The local mean background count rate was 149 (+2, -3) counts/s. Using cumulative rates, we measure a T90 of 9.3 (+0.5, -0.4) s. The source was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2025-09-20 02:54:08.30 UTC. The measured peak count rate associated with the burst is 2813 (+106, -113) counts/s above the background in the combined data of all quadrants, with a total of 4822 (+303, -320) counts. The local mean background count rate was 1366 (+7, -7) counts/s. We measure a T90 of 8.7 (+0.7, -0.4) s from the cumulative Veto light curve. CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, URSC, IUCAA, SAC, and PRL. The Indian Space Research Organisation funded, managed, and facilitated the project. CZTI GRB detections are reported regularly on the payload site at: http://astrosat.iucaa.in/czti/?q=grb View this GCN Circular online at https://gcn.nasa.gov/circulars/41899. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39964] GRB 250920B: Swift detection of a burst with a bright optical counterpart.
by GCN Circulars 20 Sep '25

20 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41898 SUBJECT: GRB 250920B: Swift detection of a burst with a bright optical counterpart. DATE: 25/09/20 09:01:06 GMT FROM: K.L. Page at U Leicester <klp5(a)leicester.ac.uk> R. Gupta (NASA GSFC), C. Gronwall (PSU), N. P. M. Kuin (UCL-MSSL) and K. L. Page (U Leicester) report on behalf of the Neil Gehrels Swift Observatory Team: At 08:46:30 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 250920B (trigger=1351008). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 187.337, +47.844 which is RA(J2000) = 12h 29m 21s Dec(J2000) = +47d 50' 39" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed multiple peaks, with a complex structure with a duration of about 150 sec. The peak count rate was ~8200 counts/sec (15-350 keV), at ~5 sec after the trigger. The XRT began observing the field at 08:48:01.1 UT, 90.6 seconds after the BAT trigger. XRT found a bright, uncatalogued X-ray source located at RA, Dec 187.3179, 47.8372 which is equivalent to: RA(J2000) = 12h 29m 16.30s Dec(J2000) = +47d 50' 13.9" with an uncertainty of 4.7 arcseconds (radius, 90% containment). This location is 52 arcseconds from the BAT onboard position, within the BAT error circle. No event data are yet available to determine the column density using X-ray spectroscopy. The initial flux in the 2.5 s image was 8.20e-09 erg cm^-2 s^-1 (0.2-10 keV). UVOT took a finding chart exposure of 150 seconds with the White filter starting 98 seconds after the BAT trigger. There is a candidate afterglow in the rapidly available 2.7'x2.7' sub-image at RA(J2000) = 12:29:16.07 = 187.31697 DEC(J2000) = +47:50:14.4 = 47.83734 with a 90%-confidence error radius of about 0.74 arc sec. This position is 2.3 arc sec. from the center of the XRT error circle. The estimated magnitude is 13.75 with a 1-sigma error of about 0.14. No correction has been made for extinction. Burst Advocate for this burst is R. Gupta (rahulbhu.c157 AT gmail.com) 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/41898. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39963] GRB 250920B: Fermi GBM Final Real-time Localization
by GCN Circulars 20 Sep '25

20 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41897 SUBJECT: GRB 250920B: Fermi GBM Final Real-time Localization DATE: 25/09/20 08:56:46 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 08:46:26 UT on 20 Sep 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250920B (trigger 780050791.161292 / 250920366). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 190.8, Dec = 47.4 (J2000 degrees, equivalent to J2000 12h 43m, 47d 23'), with a statistical uncertainty of 2.4 degrees. The angle from the Fermi LAT boresight is 56.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250920366/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250920366/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250920366/… View this GCN Circular online at https://gcn.nasa.gov/circulars/41897. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39962] GRB 250920A: BALROG localization (Fermi Trigger 780029651 / GRB 250920121)
by GCN Circulars 19 Sep '25

19 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41896 SUBJECT: GRB 250920A: BALROG localization (Fermi Trigger 780029651 / GRB 250920121) DATE: 25/09/20 05:33:44 GMT FROM: Jochen Greiner at MPE <jcgrog(a)mpe.mpg.de> T. Preis (University of Innsbruck) & J. Greiner (MPE Garching) report: The public trigdat data of the Fermi Gamma-ray Burst Monitor (GBM) trigger 780029651 at 02:54:06 on 20 Sept. 2025 were automatically fitted for spectrum and sky location with BALROG (Burgess et al. 2018, MNRAS 476, 1427; Berlato et al. 2019, ApJ 873, 60). The best-fit position is: RA(2000.0) = 174.6 deg Decl.(2000.0) = 52.8 deg The 1 sigma statistical error radius is 1.9 deg. We estimate an additional systematic error of 2 deg. Further details are available at: https://grb.mpe.mpg.de/grb/GRB250920121/ The Healpix map can be downloaded from: https://grb.mpe.mpg.de/grb/GRB250920121/healpix The location parameters are available as JSON at: https://grb.mpe.mpg.de/grb/GRB250920121/json View this GCN Circular online at https://gcn.nasa.gov/circulars/41896. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39961] GRB 250920A: Fermi GBM Final Localization
by GCN Circulars 19 Sep '25

19 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41895 SUBJECT: GRB 250920A: Fermi GBM Final Localization DATE: 25/09/20 05:05:52 GMT FROM: Jacob Smith at Fermi-GBM Team <jrs0118(a)uah.edu> The Fermi GBM team reports the detection of a likely LONG GRB "At 02:54:06.82 UT on 20 September 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250920 (trigger 780029651/250920121). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 175.27, Dec = 48.96 (J2000 degrees, equivalent to J2000 11h 41m, +48d 57'), with a statistical uncertainty of 1.00 degrees. The angle from the Fermi LAT boresight is 88 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250920121/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250920121/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250920121/…" View this GCN Circular online at https://gcn.nasa.gov/circulars/41895. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39960] GRB 250919A/EP250919a: SVOM/VT optical observation
by GCN Circulars 19 Sep '25

19 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41894 SUBJECT: GRB 250919A/EP250919a: SVOM/VT optical observation DATE: 25/09/20 02:42:26 GMT FROM: Yinuo Ma <mayn(a)bao.ac.cn> Y. N. Ma, L. P. Xin, Z. H. Yao, Y. L. Qiu, C. Wu, H. L. Li, X. H. Han, Y. Xu, J. Wang, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA) report on behalf of the SVOM/VT team. SVOM performed a Target of Opportunity observation of GRB 250919A/EP250919a detected by Fermi/GBM, SVOM/GRM, EP/WXT, NuSTAR, and Glowbug (Fermi GBM team GCN 41874; Wang et al., GCN 41882; Liang et al., GCN 41879; Waratkar & Grefenstette, GCN 41888; Cheung et al., GCN 41891). SVOM/VT began observing the field at 2025-09-19T14:24:05 UTC, 13.92 hours after the trigger, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. With X-band data available, the optical counterpart (Li et al., GCN 41877; Levan et al., GCN 41883; Oates et al., GCN 41886; Lipunov et al., GCN 41893) was clearly detected in both VT_B and VT_R bands. The magnitudes are: mid time (h) | exposure time (s) | band | mag (AB) | mag err -------------|-------------------|------|----------|-------- 14.240 | 47*50 | VT_B | 18.55 | 0.02 14.247 | 46*50 | VT_R | 18.13 | 0.02 Our photometry was not corrected for Galactic extinction. The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS. View this GCN Circular online at https://gcn.nasa.gov/circulars/41894. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39959] GRB 250919A / EP250919a: MASTER bright afterglow detection 24h after GRB time
by GCN Circulars 19 Sep '25

19 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41893 SUBJECT: GRB 250919A / EP250919a: MASTER bright afterglow detection 24h after GRB time DATE: 25/09/20 00:38:17 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.M.Lipunov (Lomonosov MSU, Moscow), R.Podesta, C.Francile, F. Podesta, E. Gonzalez (OAFA), A.Kuznetsov, A.Sankovich, G.Antipov, P.Balanutsa, E.Gorbovskoy, N.Tiurina, M.Shilova, A.Chasovnikov, V.Topolev, K.Zhirkov, Ya.Kechin, V.Senik, D.Vlasenko(Lomonosov MSU), D.Buckley, (SAAO, South Africa) O.Gress, N.Budnev (ISU, Irkutsk), A.Sosnovskij (Crao RAS), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), V.M.Pillet, R.Rebolo Lopez (The Instituto de Astrofisica de Canarias, Spain), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez,J.Martinez,A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysic Observatory, Mexico) MASTER Global robotic Net (Lipunov et al. 2010) started Fermi GRB 250919A (GBM GCN 41874, GCN 41876, GCN 41890; LAT GCN 41884, Ttrigger=00:28:52) observation in alert mode (Lipunov et al. GCN 41875) at MASTER-OAFA and continued as EP GRB 250919 (GCN 41879) since its notice time (Lipunov et al. 41880) Bright optical counterpart MASTER OT J195412.89-485016.4 was detected with peak structure light curve. 24h after GRB detection (GCN 41874) this optical counterpart has unfiltered m_OT~18.3 MASTER observations will be continued This transient was first publishied as EP250919a optical counterpart by Las Cumbres observatory (GCN 41877, t_detection=03:02:52.800 UTC) and as Fermi GRB 250919A/EP250919a optical counterpart by Gemini-South (LEvan et al. GCN 41883) with reshift detection z = 1.145 X-ray counterpart was also detected by Swift (Osborne et al. GCN 41885) with OT afterglow detection by UVOT (Oates et al. GCN 41886), . NuSTAR (GCN 41888) and Svom (41882). View this GCN Circular online at https://gcn.nasa.gov/circulars/41893. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39958] GRB 250916A: Mondy R-band optical observations
by GCN Circulars 19 Sep '25

19 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41892 SUBJECT: GRB 250916A: Mondy R-band optical observations DATE: 25/09/19 20:44:29 GMT FROM: Nicolai Pankov at HSE, IKI RAS <colinsergesen(a)gmail.com> N. Pankov (HSE, IKI), A. Pozanenko (IKI), E. Klunko (ISTP) A. Moskvitin (SAO RAS) report on behalf of IKI-GRB-FuN: We observed the field of a long GRB 250916A at the redshift z = 2.015 (de Ugarte Postigo et al., GCN 41863) detected by Fermi/GBM (The Fermi GBM team, GCN 41839), AstroSat/CZTI (Arya et al., GCN 41843), Glowbug (Cheung et al., GCN 41855), Swift/XRT (Osborne et. al, GCN 41862), and NuSTAR (Waratkar et. al, GCN 41871). The observations were carried with the AZT-33IK 1.5m reflector of Sayan Solar Observatory (Mondy) equipped with the CMOS-photometer. The series of 25x120 s images was obtained in the R-band starting on 2025-09-18 at 18:36 UT, i.e. ~2.23 days since GRB. In the stacked image we clearly detect the OT found initially by GOTO (Belkin et al., GCN 41847) and followed-up by (Mohan et al., GCN 41858; Moskvitin et. al, GCN 41859; Burkhonov et al., GCN 41860; Moskvitin et. al, GCN 41870; Zheng & Filippenko, GCN 41873). Preliminary observation results are presented below: Date UT start t-T0 Exp. Filter OT Err. UL (mid, days) (n*s) (3sigma) 2025-09-18 18:36:27 2.23063 25x120 R 20.52 0.02 21.5 The photometry is based on nearby stars of PanSTARRS-DR1 (R-magnitudes were obtained via the Lupton 2005 transformations; see Moskvitin et. al, GCN 41859) and not corrected for the Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/41892. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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