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

[vsnet-grb-info 39983] GRB 250920C: Fermi GBM Observation
by GCN Circulars 20 Sep '25

20 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41917 SUBJECT: GRB 250920C: Fermi GBM Observation DATE: 25/09/20 20:46:55 GMT FROM: Bagrat Mailyan at Florida Tech <mbagrat(a)gmail.com> B. Mailyan (Florida Tech) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 15:25:17.06 UT on 20 September 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250920C (trigger 780074722/250920643) which was also detected by Swift BAT (R. Gupta et al. 2025, GCN 41904). The Fermi GBM Final Real-time Localization (GCN 41903) is consistent with the Swift BAT position. The angle from the Fermi LAT boresight is 94 degrees. The GBM light curve consists of multiple emission episodes with a duration (T90) of about 36.6 s (50-300 keV). The time-averaged spectrum from T0+0.003 to T0+37.377 s is best fit by a Band function with Epeak = 117 +/- 4 keV, alpha = -0.76 +/- 0.04, and beta = -2.34 +/- 0.05. The event fluence (10-1000 keV) in this time interval is (2.97 +/- 0.04)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+26 s in the 10-1000 keV band is 25.1 +/- 0.5 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog: https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html For Fermi GBM data and info, please visit the official Fermi GBM Support Page: https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/" View this GCN Circular online at https://gcn.nasa.gov/circulars/41917. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39982] Swift GRB 250920C: Global MASTER-Net observations report
by GCN Circulars 20 Sep '25

20 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41916 SUBJECT: Swift GRB 250920C: Global MASTER-Net observations report DATE: 25/09/20 19:34:22 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-SAAO robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in South Africa (South African Astronomical Observatory) was pointed to the Swift GRB 250920C ( R. Gupta et al., GCN 41904) errorbox 13198 sec after notice time and 13225 sec after trigger time at 2025-09-20 19:05:42 UT, with upper limit up to 18.1 mag. The observations began at zenith distance = 85 deg. The sun altitude is -32.4 deg. The galactic latitude b = -56 deg., longitude l = 226 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2996190 We obtain a following upper limits. Tmid-T0 | Site |Filt.| Expt. | Limit| Comment _________|_____________________|_____|_______|______|________ 13315 | MASTER-SAAO | C | 180 | 14.4 | 14583 | MASTER-SAAO | C | 180 | 15.6 | 14583 | MASTER-SAAO | C | 180 | 18.1 | 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/41916. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39981] GRB 250920B: Swift/UVOT Detection
by GCN Circulars 20 Sep '25

20 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41915 SUBJECT: GRB 250920B: Swift/UVOT Detection DATE: 25/09/20 19:22:10 GMT FROM: Paul Kuin at MSSL <npkuin(a)gmail.com> Paul Kuin (MSSL) and Rahul Gupta (NASA GSFC) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 250920B 99 s after the BAT trigger (Gupta et al., GCN Circ. 41898). A source consistent with the XRT position (Evans et al. GCN. Circ. 41910) is detected in the initial UVOT exposures. The preliminary UVOT position is: RA (J2000) = 12:29:16.07 = 187.31697 (deg.) Dec (J2000) = +47:50:14.4 = 47.83732 (deg.) with an estimated uncertainty of 0.42 arc sec. (radius, 90% confidence). Preliminary detections and 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag white 99 249 147 13.89 +/- 0.02 v 4433 4633 197 16.53 +/- 0.05 b 3818 4018 197 16.62 +/- 0.04 u 311 452 139 13.26 +/- 0.02 w1 4843 5043 197 17.02 +/- 0.08 m2 4638 4838 197 >19.2 w2 4228 4428 197 19.21 +/- 0.25 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.011 in the direction of the burst (Schlegel et al. 1998). The observation also included a 49s long UV grism exposure. Inspection of the noisy grism spectrum suggests a redshift of 2.2 based on identifying an broad absorption with the the Ly-alpha line. View this GCN Circular online at https://gcn.nasa.gov/circulars/41915. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39980] GRB 250920B: FTW optical and NIR observations of the counterpart
by GCN Circulars 20 Sep '25

20 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41914 SUBJECT: GRB 250920B: FTW optical and NIR observations of the counterpart DATE: 25/09/20 19:17:41 GMT FROM: Xander J Hall at Carnegie Mellon University <xjh(a)andrew.cmu.edu> Xander J Hall (Carnegie Mellon U.), Malte Busmann (LMU), Brendan O’Connor (Carnegie Mellon U.), Daniel Gruen (LMU), and Antonella Palmese (Carnegie Mellon U.) report: We observed the counterpart of GRB 250920B (Fermi GBM Team, GCN 41897; Gupta et al., GCN 41898; Wu et al., GCN 41908) with the Three Channel Imager (3KK) at the Fraunhofer Telescope at Wendelstein Observatory (FTW) in the r, i and J band simultaneously for 10 x 60s starting at 2025-09-20 18:19:54 UT (0.4 days after the trigger). We detect the counterpart clearly in all filters and report the following magnitude: r = (18.81 +/- 0.01) mag. The magnitude is calibrated against the PS1 catalog. All magnitudes are provided in the AB system and are not corrected for Galactic extinction. We thank Christoph Ries and Ralf Bender from the Wendelstein Observatory for obtaining these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/41914. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39979] GRB 250920C: Optical counterpart detection by LCO
by GCN Circulars 20 Sep '25

20 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41913 SUBJECT: GRB 250920C: Optical counterpart detection by LCO DATE: 25/09/20 18:32:10 GMT FROM: ankur ghosh at CAPP, University of Johannesburg <ghosh.ankur1994(a)gmail.com> Ankur Ghosh, Soebur Razzaque (CAPP, University of Johannesburg), Rahul Gupta (NASA GSFC), Alexander Moskvitin, Yulia Sotnikova (SAO RAS), Naveen Dukiya (ARIES) on behalf of a larger collaboration. We observed the field of the GRB 250920C triggered by the Swift (Gupta et al., GCN 41904) in the r, V filter of the 1-meter Sinistro telescope at the Las Cumbres Observatory Global Telescope (LCOGT) node located at Siding Spring is near Coonabarabran, New South Wales, Australia . The 1-m Sinistro telescope is equipped with a 4K x 4K CCD (FOV: 26 x 26 arcmin, scale: 0.39 arcsec/pixel). Observations began on September 20, 2025, starting 1.47 hours after the GRB trigger. Further observations are currently ongoing. We clearly detect the optical transient (OT) reported by GCNs (Wortley et al., GCN 41907, Strausbaugh et al., GCN 41911) in our r and V band image. |Date| |JDstart| |t-T0 (hours)| |Exp (sec)| |Filter| |Magnitude| ---------------------------------------------------------------------------------------------------- 2025-09-20 2460939.20389 1.47 1 x 600 r r = 18.47 +/- 0.01 2025-09-20 2460939.22762 2.04 1 x 600 r r = 18.75 +/- 0.01 The field was calibrated against nearby APASS stars, with magnitudes converted using Lupton (2005) equations, and has not been corrected for Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/41913. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39978] GRB 250920A: SVOM/GRM observation
by GCN Circulars 20 Sep '25

20 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41912 SUBJECT: GRB 250920A: SVOM/GRM observation DATE: 25/09/20 18:19:32 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: Jean-Luc Atteia (IRAP) Report on behalf of the SVOM team: SVOM/GRM was triggered in-flight by a bright burst GRB 250920A (SVOM trigger reference: sb25092001) at 2025-09-20T02:54:09.000 UTC (T0), which is also detected by Fermi/GBM (Fermi GBM Team, GCN#41895) and AstroSat (Harsha K. H., GCN#41899). With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of multi-pulses with a T90 of 9.6 +0.3/-0.1 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb250920A.png In addition, the position of this burst, as determined by Fermi/GBM (RA= 175.27, DEC= 48.96, GCN#41895), is located at about 144 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view, but this burst still clearly detected by ECLAIRs through the shield. With this localization, the time-averaged spectrum from T0-3 to T0+11 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.58 +0.06/-0.06 and the cutoff energy, parameterized as Epeak, is 202 +17/-13 keV. The event fluence (10-1000 keV) in this time interval is (6.24 +0.14/-0.13)E-05 erg/cm^2. The localization of GRB 250919A in the 'Amati' relation diagram is shown at: https://www.bursthub.cn//admin/static/svgrb250920A_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/41912. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39977] GRB250920C: LCOGT Optical Detection
by GCN Circulars 20 Sep '25

20 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41911 SUBJECT: GRB250920C: LCOGT Optical Detection DATE: 25/09/20 17:10:36 GMT FROM: Robert Strausbaugh at Eastern Illinois University <rstrausbaugh(a)eiu.edu> R. Strausbaugh (Eastern Illinois University), A. Cucchiara (NASA) report on behalf of a larger collaboration: We observed the Swift GRB 250920C field (Gupta et al., GCN 41904) with the LCOGT 1-meter Sinistro instrument at the Siding Spring Observatory, Australia site, on September 20, from 16:29 to 16:51 UT (corresponding to 1.07 to 1.26 hours after the GRB trigger time) with the SDSS r and i filters. We performed a series of 3x200s exposures in i-band and r-band. We detect an uncatalogued source consistent with GOTO optical counterpart candidate (Wortley et al., GCN 41907) in both bands. The following magnitudes are calculated using the PanSTARRS catalog as reference: r = 18.54 +/- 0.05 i = 18.25 +/- 0.01 These magnitudes are not corrected for galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/41911. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39976] GRB 250920B: Enhanced Swift-XRT position
by GCN Circulars 20 Sep '25

20 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41910 SUBJECT: GRB 250920B: Enhanced Swift-XRT position DATE: 25/09/20 17:03:19 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> P.A. Evans, M.R. Goad, J.P. Osborne and A.P. Beardmore (U. Leicester) report on behalf of the Swift-XRT team. Using 1850 s of XRT Photon Counting mode data and 5 UVOT images for GRB 250920B, we find an astrometrically corrected X-ray position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 187.31688, +47.83750 which is equivalent to: RA (J2000): 12h 29m 16.05s Dec (J2000): +47d 50' 15.0" with an uncertainty of 1.9 arcsec (radius, 90% confidence). This position may be improved as more data are received. The latest position can be viewed at http://www.swift.ac.uk/xrt_positions. Position enhancement is described by Goad et al. (2007, A&A, 476, 1401) and Evans et al. (2009, MNRAS, 397, 1177). This circular was automatically generated, and is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/41910. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39975] GRB 250920B: Swift-XRT refined Analysis
by GCN Circulars 20 Sep '25

20 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41909 SUBJECT: GRB 250920B: Swift-XRT refined Analysis DATE: 25/09/20 16:55:32 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> K.L. Page (U. Leicester), R. Brivio (INAF-OAB), A. D'Ai (INAF-IASFPA), S. Campana (INAF-OAB), S. Dichiara (PSU), J.A. Kennea (PSU), D.N. Burrows (PSU), A.P. Beardmore (U. Leicester) and P.A. Evans report on behalf of the Swift-XRT team: We have analysed 6.4 ks of XRT data for GRB 250920B, from 87 s to 22.3 ks after the trigger. The data comprise 395 s in Windowed Timing (WT) mode (the first 2 s were taken while Swift was slewing) with the remainder in Photon Counting (PC) mode. The refined XRT position is RA, Dec = 187.3175, +47.8376 which is equivalent to: RA (J2000): 12h 29m 16.21s Dec(J2000): +47d 50' 15.2" with an uncertainty of 3.5 arcsec (radius, 90% confidence). The late-time light curve (from T0+3.8 ks) can be modelled with a power-law decay with a decay index of alpha=1.20 (+/-0.05). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 1.490 (+0.035, -0.017). The best-fitting absorption column is consistent with the Galactic value of 1.1 x 10^20 cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 1.89 (+/-0.07) and a best-fitting absorption column of 3.3 (+1.5, -1.4) x 10^20 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.5 x 10^-11 (3.7 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 3.3 (+1.5, -1.4) x 10^20 cm^-2 Galactic foreground: 1.1 x 10^20 cm^-2 Excess significance: 2.5 sigma Photon index: 1.89 (+/-0.07) If the light curve continues to decay with a power-law decay index of 1.20, the count rate at T+24 hours will be 0.10 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 3.5 x 10^-12 (3.8 x 10^-12) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01351008. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/41909. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39974] GRB 250920B: SVOM/C-GFT optical observations
by GCN Circulars 20 Sep '25

20 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41908 SUBJECT: GRB 250920B: SVOM/C-GFT optical observations DATE: 25/09/20 16:38:42 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Chao WU (NAOC), Zhe Kang (CHO), Liping Xin(NAOC), Xuhui Han(NAOC), Pinpin Zhang (NAOC), Xiaomeng Lu (NAOC), Zhenwei Li (CHO), You Lv (CHO), Ruosong Zhang (NAOC), Yujie Xiao(NAOC), Yulei Qiu (NAOC), Jing Wang (NAOC), Jinsong Deng(NAOC), Lei Huang(NAOC), Jianyan Wei (NAOC), report on behalf of the SVOM/C-GFT team: We observed the field of GRB 250920B detected by Fermi/GBM (Fermi Team, GCN 41897) and Swift/BAT (Gupta et al., GCN 41898) with LATIOS on SVOM/C-GFT. Observations started at 2025-09-20 11:22:32.815 UTC, ~2.60 hr after the trigger. The optical counterpart reported by Gupta et al.(GCN 41898) was clearly detected in our stacked images of band g, r, and i. The magnitudes are: | mid-time (T-T₀) / hr | exposure time / s | band | mag (AB) | mag err | |:---------------------|:------------------|:-----|:---------|:--------| | 2.76 | 10×30 | g | 17.15 | ±0.07 | | 2.64 | 10×30 | r | 17.05 | ±0.07 | | 2.85 | 9×30 | i | 17.01 | ±0.05 | The photometry was calibrated with nearby Pan-STARRS1 stars. Magnitudes were not corrected for dust extinction. We thank the observation assistants Shuai Liu and Chunlei Guo at Jilin observatory for their excellent support. The Chinese Ground Follow-up Telescope (C-GFT) for the SVOM mission is located at Jilin Station, Changchun Observatory, National Astronomical Observatories, CAS. It features two instruments: (1) CATCH at the Cassegrain focus with a 21 arcsec x 21 arcsec FOV for simultaneous g/r/i-band imaging, and (2) LATIOS, a 4k x 4k CMOS camera at the prime focus with a 1.28 deg x 1.28 deg FOV that images in g, r, and i bands via filter switching. View this GCN Circular online at https://gcn.nasa.gov/circulars/41908. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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