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

[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 20 Sep '25

20 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 20 Sep '25

20 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 20 Sep '25

20 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 20 Sep '25

20 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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[vsnet-grb-info 39957] GRB 250919A: Glowbug gamma-ray detection
by GCN Circulars 19 Sep '25

19 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41891 SUBJECT: GRB 250919A: Glowbug gamma-ray detection DATE: 25/09/19 18:58:32 GMT FROM: C.C. Cheung at Naval Research Lab <Teddy.Cheung(a)nrl.navy.mil> C.C. Cheung, R. Woolf, M. Kerr, J.E. Grove (NRL), A. Goldstein (USRA), C.A. Wilson-Hodge, D. Kocevski (MSFC), and M.S. Briggs (UAH) report: The Glowbug gamma-ray telescope [1,2,3], operating on the International Space Station, reports the detection of GRB 250919A, which was also detected by Fermi/GBM (GCN 41874, 41881, 41890), SVOM/GRM (GCN 41882), and NuSTAR (GCN 41888), and associated with the Einstein Probe transient EP250919a (GCN 41879). Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2025-09-19 00:28:56.288 with a duration of 32.1 s and a total significance of about 14.5 sigma. The burst originated toward the Nadir side of Glowbug and was detected despite passing through the passive material from the H9 pallet and internal passive material/shielding within Glowbug. The observed light curve comprises two primary peaks at ~T0+24s and ~T0+28s. Note that data from ~T0+30s to +38s suffered from deadtime in various detectors. The analysis results presented here are preliminary and use a response function that lacks a detailed characterization of the surrounding passive structure of the ISS. Glowbug is a NASA-funded technology demonstrator for sensitive, low-cost gamma-ray transient telescopes developed, built, and operated by the U.S. Naval Research Laboratory (NRL) with support from the University of Alabama in Huntsville, USRA, and NASA MSFC. It was launched on 2023 March 15 aboard the Department of Defense Space Test Program’s STP-H9 to the ISS, and operated until 2024 April when it was put in safe storage on orbit. Glowbug was recently removed from storage and resumed operation on 2025 September 12. [1] Grove, J.E. et al. 2020, Proc. Yamada Conf. LXXI, arXiv:2009.11959 [2] Woolf, R.S. et al. 2022, Proc. SPIE, 12181, id. 121811O [3] Woolf, R.S. et al. 2024, Proc. SPIE, 13151, id. 1315108 Distribution Statement A: Approved for public release. Distribution is unlimited. View this GCN Circular online at https://gcn.nasa.gov/circulars/41891. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39956] GRB 250919A: Fermi GBM Observation
by GCN Circulars 19 Sep '25

19 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41890 SUBJECT: GRB 250919A: Fermi GBM Observation DATE: 25/09/19 18:56:13 GMT FROM: oindabimukherjee(a)gmail.com O. Mukherjee (USRA) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 00:28:52.28 UT on 19 September 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250919A (trigger 779934537/250919020) which was also detected by Fermi-LAT ( A. Holzmann Airasca et al. 2025, GCN 41884), SVOM-GRM (Chen-Wei Wang et al. 2025, GCN 41882), Swift-XRT (J.P. Osborne et al., 2025, GCN 41885), EP-WXT (Y.F. Liang et al. 2025, GCN 41879), Swift-UVOT (S.R. Oates et al. 2025, GCN 41886), Gemini/GMOS-S spectroscopic redshift z = 1.145 (A. J. Levan et al. 2025, GCN 41883) The Fermi GBM on-ground location is consistent with the position measured by other instruments. The angle from the Fermi LAT boresight is 56 degrees. The GBM light curve consists of a very bright emission episode, followed by a fainter second emission episode, with a total duration (T90) of about 129.3 s (50-300 keV). The time-averaged spectrum from T0+3 to T0+190 s is best fit by a Band function with Epeak = 476 +/- 6 keV, alpha = -0.88 +/- 0.01, and beta = -2.39 +/- 0.04. The event fluence (10-1000 keV) in this time interval is (4.36 +/- 0.002)E-04 erg/cm^2. The 1-sec peak photon flux measured starting from T0+33 s in the 10-1000 keV band is 115.2 +/- 0.7 ph/s/cm^2. The time-averaged spectrum of the main pulse from T0+3 to T0+58 s is best fit by a Band function with Epeak = 475 +/- 5 keV, alpha = -0.7 +/- 0.01, and beta = -2.38 +/- 0.03. The event fluence (10-1000 keV) in this time interval is (2.56 +/- 0.01)E-04 erg/cm^2. The time-averaged spectrum of the second pulse from T0+111 to T0+190 s is best fit by a Band function with Epeak = 220 +/- 12 keV, alpha = -1.12 +/- 0.02, and beta = -1.93 +/- 0.03. The event fluence (10-1000 keV) in this time interval is (5.77 +/- 0.05)E-05 erg/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/41890. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39955] Fermi GRB 250918A: Global MASTER-Net observations report
by GCN Circulars 19 Sep '25

19 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41889 SUBJECT: Fermi GRB 250918A: Global MASTER-Net observations report DATE: 25/09/19 18:30:47 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) started inspect of the Fermi GRB 250918A ( Fermi GBM team, GCN 41865) errorbox 1 days 18846 sec after notice time and 1 days 18882 sec after trigger time at 2025-09-19 17:47:00 UT, with upper limit up to 15.6 mag. Observations started at twilight. The observations began at zenith distance = 60 deg. The sun altitude is -16.5 deg. The galactic latitude b = 38 deg., longitude l = 340 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2994371 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 105313 | 2025-09-19 17:47:00 | MASTER-SAAO | (14h 44m 17.11s , -15d 37m 24.9s) | C | 60 | 15.6 | 105313 | 2025-09-19 17:47:00 | MASTER-SAAO | (14h 46m 06.96s , -15d 52m 16.6s) | C | 60 | 14.9 | 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/41889. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 39954] GRB 250919A / EP250919a: NuSTAR detection of bright prompt emission
by GCN Circulars 19 Sep '25

19 Sep '25

TITLE: GCN CIRCULAR NUMBER: 41888 SUBJECT: GRB 250919A / EP250919a: NuSTAR detection of bright prompt emission DATE: 25/09/19 18:19:52 GMT FROM: Gaurav Waratkar at Caltech <gauravwaratkar(a)iitb.ac.in> G. Waratkar (Caltech) and B. Grefenstette (Caltech) report on behalf of the NuSTAR Search for INteresting Gamma-ray Signals (SINGS) working group: The NuSTAR SINGS working group reports the detection of prompt emission from the long-duration GRB 250919A in both the NuSTAR CsI anti-coincidence shields. This GRB was identified through a blind search using the CsI shield rates. Details of the search algorithm will be described in a future paper. The NuSTAR SINGS algorithm triggered at 2025-09-19T00:29:12.000 (with a resolution ~5-seconds). This is consistent with the detections of GRB 250919A by Fermi/GBM (Fermi GBM Team, GCN Circ. 41874), SVOM/GRM (Wang et al., GCN Circ. 41882), associated with EP250919a detected by EP/WXT (Liang et al., GCN Circ. 41879). The NuSTAR CsI shield data are recorded at 1 Hz. The burst appears to be composed of a very bright peak lasting for ~20-s, followed 75-s later by a relatively fainter burst episode lasting for ~50-s. The peak count rate is ~9000-cps over a baseline rate of ~1,000-cps during this time period. We also see clear evidence in the signal above 100 keV in the CdZnTe detectors for the first episode. The localization from the counterpart candidate (Li et al., GCN Circ. 41877; Levan et al., GCN Circ. 41883; Airasca et al., GCN Circ. 41884; Osborne et al., GCN Circ. 41885, Oates et al., GCN Circ. 41886) at RA = 298.52, Dec = -48.83 implies an offset from the NuSTAR boresight of 33-deg and the offset from the geocenter of 74-deg. Lightcurves and analysis for this GRB can be found here: https://nustarsoc.caltech.edu/NuSTAR_Public/grbs/reports/2025/250919A/ Information on NuSTAR SINGS can be found here: https://nustarsoc.caltech.edu/NuSTAR_Public/grbs/ NuSTAR is a NASA Small Explorer mission led by Caltech and managed by JPL for NASA's Science Mission Directorate in Washington. View this GCN Circular online at https://gcn.nasa.gov/circulars/41888. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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