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

[vsnet-grb-info 40460] GRB 251016B: Fermi GBM Detection
by GCN Circulars 23 Oct '25

23 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42383 SUBJECT: GRB 251016B: Fermi GBM Detection DATE: 25/10/23 06:22:48 GMT FROM: Matt Godwin <msg0028(a)uah.edu> Matt Godwin (UAH) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 23:59:00.72 UT on 16 October 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251016B (trigger 782351945/251016999). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 183.64, Dec = 59.60 (J2000 degrees, equivalent to J2000 12h 14m, +59d 36'), with a statistical uncertainty of 1.00 degrees. (radius, 1-sigma containment, statistical only; there is additionally a systematic error which we have characterized as a mixture of two Gaussians, one with a radius of 1.8 degrees (52% contribution) and one with a radius of 4.1 degrees (47% contribution) [A. Goldstein et al. 2020, ApJ, 895, 1]). The angle from the Fermi LAT boresight is 46 degrees. The GBM light curve consists of a single bright emission episode with a duration (T90) of about 7.1 s (50-300 keV). The time-averaged spectrum from T0-0.8 to T0+13.5 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -1.07 +/- 0.01 and the cutoff energy, parameterized as Epeak, is 310 +/- 1 keV. The event fluence (10-1000 keV) in this time interval is (2.27 +/- 0.05)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+2.4 s in the 10-1000 keV band is 37.5 +/- 0.5 ph/s/cm^2. A Band function fits the spectrum equally well with Epeak= 222 +/- 1 keV, alpha = -0.96 +/- 0 and beta = -2 +/- 0.01. 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/42383. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40459] GRB 251022A: Tiled Swift observations
by GCN Circulars 22 Oct '25

22 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42382 SUBJECT: GRB 251022A: Tiled Swift observations DATE: 25/10/23 05:56:57 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 team: Swift has initiated a series of observations, tiled on the sky, of the Fermi/LAT GRB 251022A. Automated analysis of the XRT data will be presented online at https://www.swift.ac.uk/xrt_products/TILED_GRB00139 Any uncatalogued X-ray sources detected in this analysis will be reported on this website and via GCN COUNTERPART notices. The probability of finding serendipitous sources, unrelated to the Fermi/LAT event is high: any X-ray source considered to be a probable afterglow candidate will be reported via a GCN Circular after manual consideration. Details of the XRT automated analysis methods are detailed in Evans et al. (2007, A&A, 469, 379; 2009, MNRAS, 397, 1177 and 2014, ApJS, 210, 8). This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/42382. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40458] LAT GRB251022.94: Global MASTER-Net observations report
by GCN Circulars 22 Oct '25

22 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42381 SUBJECT: LAT GRB251022.94: Global MASTER-Net observations report DATE: 25/10/23 03:11:21 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-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 LAT GRB251022.94 (trigger No 782865260,04h 21m 31.18s , -19d 18m 35.6s, R=0.32) errorbox 13 sec after notice time and 16215 sec after trigger time at 2025-10-23 03:04:30 UT, with upper limit up to 17.2 mag. Observations started at twilight. The observations began at zenith distance = 32 deg. The sun altitude is -10.1 deg. The galactic latitude b = -41 deg., longitude l = 216 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3021522 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 16245 | 2025-10-23 03:04:30 | MASTER-SAAO | (04h 21m 02.62s , -19d 31m 07.4s) | C | 60 | 17.2 | 16245 | 2025-10-23 03:04:30 | MASTER-SAAO | (04h 19m 05.26s , -19d 15m 42.2s) | P\ | 60 | 16.7 | 16324 | 2025-10-23 03:05:49 | MASTER-SAAO | (04h 21m 02.39s , -19d 31m 03.5s) | C | 60 | 16.7 | 16324 | 2025-10-23 03:05:49 | MASTER-SAAO | (04h 19m 05.05s , -19d 15m 37.8s) | P\ | 60 | 16.6 | 16404 | 2025-10-23 03:07:08 | MASTER-SAAO | (04h 19m 04.85s , -19d 15m 33.5s) | P\ | 60 | 16.6 | 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/42381. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40457] GRB 251022A: Fermi GBM Final Real-time Localization
by GCN Circulars 22 Oct '25

22 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42380 SUBJECT: GRB 251022A: Fermi GBM Final Real-time Localization DATE: 25/10/22 22:44:50 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 22:34:15 UT on 22 Oct 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251022A (trigger 782865260.264246 / 251022940). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 74.5, Dec = -22.7 (J2000 degrees, equivalent to J2000 04h 58m, -22d 41'), with a statistical uncertainty of 1.9 degrees. The angle from the Fermi LAT boresight is 29.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251022940/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251022940/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251022940/… View this GCN Circular online at https://gcn.nasa.gov/circulars/42380. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40456] GRB 251013C: SAO RAS optical observations
by GCN Circulars 22 Oct '25

22 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42230 SUBJECT: GRB 251013C: SAO RAS optical observations DATE: 25/10/13 21:31:40 GMT FROM: Alexander Moskvitin at SAO RAS <mosk(a)sao.ru> A. S. Moskvitin, O. I. Spiridonova, V. V. Vlasyuk (SAO RAS), N. Pankov (HSE, IKI), A. Pozanenko (IKI), A. Ghosh, S. Razzaque (CAPP, University of Johannesburg), Tao An and Yuanqi Liu (Shanghai Astronomical Observatory) report on behalf of GRB follow-up collaboration and IKI-GRB-FuN. We observed the field of the GRB 251013C (The Fermi GBM team, GCN 42221; Rakotondrainibe et al., GCN 42222) with the 1-m SAO RAS telescope Zeiss-1000 equipped with the CCD-photometer. The observations started on 2025.10.13T19:47:54 UT (t_mid - T0 = 2.1369 hours). The OT (Palmerio et al., GCN 42223; Perez-Garcia et al., GCN 42225; Konno et al., GCN 42226; Martin-Carrillo et al., GCN 42227; Masi, GCN 42228; Palmerio et al, GCN 42229) is clearly detected in the individual images with the following brightness. Date UT start t-T0 Exp. Filter OT Err. (mid, d) (s) 2025.10.13 19:47:54 0.09078 300 Rc 15.84 +/- 0.01 2025.10.13 20:04:02 0.10082 100 Rc 16.05 +/- 0.01 2025.10.13 20:15:34 0.10883 100 Rc 16.21 +/- 0.01 Preliminary photometry is based on the nearby SDSS objects (magnitudes converted with Lupton 2005 equations) and has not corrected for the Galactic extinction. The observations with the 1-m telescope in BVRI filters and also with the 0.5-m telescope AS-500/2 are ongoing. View this GCN Circular online at https://gcn.nasa.gov/circulars/42230. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40455] GRB 251021A/EP251021b: Fermi-GBM Sub-Threshold Detection
by GCN Circulars 22 Oct '25

22 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42379 SUBJECT: GRB 251021A/EP251021b: Fermi-GBM Sub-Threshold Detection DATE: 25/10/22 13:56:22 GMT FROM: mariaedvige.ravasio(a)ru.nl M. E. Ravasio (Radboud Univ.), E. Burns (LSU), and P.G. Jonker (Radboud Univ.) report on behalf of the Fermi-GBM Team: Fermi-GBM had full spatial and temporal coverage of the transient EP251021b detected by EP-WXT (Dai et al., GCN 42377). There was no Fermi-GBM onboard trigger around the EP starting time at T0=2025-10-21T14:28:05 UTC. The GBM Targeted Search [1], the most sensitive, coherent search for GRB-like signals, was run in the time interval [-50;+500] s from the EP T0. A transient was found most significantly at ~T0+7 s on a 4.096 s timescale, with a false alarm rate of 4.9e-05 Hz. The localization is consistent with the EP one, with a spatial association probability of 99.2%. Among the three spectral templates tested, the transient was best-fit with a "soft" spectrum (i.e., a Band function with Epeak = 70 keV, alpha = -1.9, beta = -3.7) for a GRB. [1] Goldstein et al. 2019 arXiv:1903.12597 View this GCN Circular online at https://gcn.nasa.gov/circulars/42379. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40454] EP251021b: BOOTES-7 optical upper limit
by GCN Circulars 22 Oct '25

22 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42378 SUBJECT: EP251021b: BOOTES-7 optical upper limit DATE: 25/10/22 09:05:45 GMT FROM: I. Perez-Garcia at Institute of Astrophysics of Andalusia <ipg(a)iaa.es> I. Perez-Garcia, S.-Y. Wu, E. Fernandez-Garcia, M. D. Caballero-Garcia, R. Sanchez-Ramirez, S. Guziy and A. J. Castro-Tirado (IAA-CSIC, Granada), C. Perez del Pulgar, A. Castellon, A. Reina (Univ. de Malaga),Y.-D. Hu (GXU), L. Hernandez-Garcia (Univ. de Valparaiso), M. Gritsevich (Univ. of Helsinki), D. R. Xiong (Yunnan Observatories of CAS), B.-B. Zhang (Nanjing Univ.) and A. Maury (Space, San Pedro de Atacama), on behalf of a larger collaboration, report: Following the detection of the fast X-ray transient EP251021b by the Einstein Probe (Dai et al. GCN 42377), the 0.6m BOOTES-7 robotic telescope at San Pedro de Atacama (Chile) observed the fast X-ray transient location starting on Oct 22, 03:57 UT (~13.08 h after trigger) in different optical bands. No new optical source is detected on the first co-added clear-filter images (mid exposure time 2025-10-22 04:07:57) within the EP/FXT 20 arcsec radius error circle down to 20.0 mag. We thank the staff at San Pedro de Atacama Celestial Explorations observatory for their excellent support. View this GCN Circular online at https://gcn.nasa.gov/circulars/42378. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40453] EP251021b: Einstein Probe detection of a fast X-ray transient
by GCN Circulars 22 Oct '25

22 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42377 SUBJECT: EP251021b: Einstein Probe detection of a fast X-ray transient DATE: 25/10/22 08:30:35 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> C. Y. Dai (NJU), Q. J. Huang(PMO), W. F. Wen (SZTU), J. H. Wu (GZHU), H. W. Pan (NAO, CAS) on behalf of the Einstein Probe (EP) team: We report on the detection of a fast X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP251021b. The transient triggered EP-WXT (ID: 01709247263) at 2025-10-21T14:28:28 (UTC). The ground analysis of the WXT data shows that the event started at T0=2025-10-21T14:28:05 (UTC) and lasted for around 30 s. The WXT position of the source is R.A. = 306.742 deg, Dec. = -38.286 deg (J2000) with an uncertainty of 2.3 arcmin in radius (90% C.L. statistical and systematic). We performed a Target-of-Opportunity observation with the Follow-up X-ray Telescope on board EP. The observation began at 2025-10-22T04:41:25 (UTC), around 14 hours after the trigger. An uncatalogued X-ray source was detected within the WXT error circle at R.A. = 306.7451 deg, Dec. = –38.3048 deg (J2000), with a positional uncertainty of 20 arcsec in radius (90% confidence level, including both statistical and systematic uncertainties). Further information will be updated when the telemetry data is received. Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). View this GCN Circular online at https://gcn.nasa.gov/circulars/42377. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40452] GRB 250911A: MAXI/GSC detection
by GCN Circulars 21 Oct '25

21 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42376 SUBJECT: GRB 250911A: MAXI/GSC detection DATE: 25/10/22 05:22:50 GMT FROM: Hitoshi Negoro at Nihon University/MAXI team <negoro.hitoshi(a)nihon-u.ac.jp> H. Negoro (Nihon U.), T. Mihara (RIKEN), M. Serino (AGU), M. Nakajima, K. Takagi, H. Takahashi, H. Nishio (Nihon U.), T. Tamagawa, N. Kawai, M. Matsuoka (RIKEN), T. Sakamoto, S. Sugita, Y. Kawakubo, H. Hiramatsu, Y. Kondo, A. Yoshida (AGU), Y. Tsuboi, H. Sugai, N. Nagashima, Y. Ishihara (Chuo U.), M. Shidatsu, C. Kang, T. Nakamoto, M. Uenishi, T. Usuki, S. Yatsuzuka (Ehime U.), I. Takahashi, Y. Yatsu (Science Tokyo), S. Nakahira, S. Ueno, H. Tomida, M. Ishikawa, S. Ogawa, M. Kurihara (JAXA), Y. Ueda, K. Fujiwara (Kyoto U.), M. Yamauchi, M. Nishio, C. Hiraizumi (Miyazaki U.), K. Yamaoka (Nagoya U.), M. Sugizaki (Kanazawa U.), W. Iwakiri (Chiba U.), T. Kawamuro (Osaka U.), and S. Yamada (Tohoku U), We report on the detection of GRB 250911A by MAXI (Swift-BAT: GCN 41781, 41812, COLIBRI: GCN 41782, Swift-XRT: GCN 41783, 41784, 41804, Swift-UVOT: 41800, MASTER: GCN 41806, GECAM-B: GCN 41813, Insight-HXMT: GCN 41827, Konus-Wind: GCN 41939). MAXI detected the burst for approximately 40 seconds, centered at around 01:29:46 on September 11, 2025. The period coincides with the main peak of the burst detected by Swift, HXMT, and Konus-Wind. The 4-10 keV X-ray flux averaged over the scan was 2041 ± 83 mCrab. The MAXI light curve is shown at https://maxi.riken.jp/grbs/250911a/ GRB 250911A was about 0.8 degrees away from the bright NS-LMXB GX 9+9. Due to the X-ray photon confusion from GX 9+9, we were unable to obtain firm upper limits or flux in the previous transit at 23:57 UT on September 10 and the next transit at 03:02 UT. Some software problem during the burst partly causes the late notice. View this GCN Circular online at https://gcn.nasa.gov/circulars/42376. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40451] LIGO/Virgo/KAGRA S251021u: Updated Sky localization
by GCN Circulars 21 Oct '25

21 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42375 SUBJECT: LIGO/Virgo/KAGRA S251021u: Updated Sky localization DATE: 25/10/21 16:18:24 GMT FROM: mattia.emma.2022(a)live.rhul.ac.uk The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report: We have conducted further analysis of the LIGO Hanford Observatory (H1) and LIGO Livingston Observatory (L1) data around the time of the compact binary merger (CBC) candidate S251021u (GCN Circular 42373). Parameter estimation has been performed using Bilby [1] and a new sky map, Bilby.multiorder.fits,0, distributed via GCN and SCiMMA notices, is available for retrieval from the GraceDB event page: https://gracedb.ligo.org/superevents/S251021u For the Bilby.multiorder.fits,0 sky map, the 90% credible region is 3859 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 5884 +/- 2089 Mpc (a posteriori mean +/- standard deviation). For further information about analysis methodology and the contents of this alert, refer to the LIGO/Virgo/KAGRA Public Alerts User Guide https://emfollow.docs.ligo.org/. [1] Ashton et al. ApJS 241, 27 (2019) doi:10.3847/1538-4365/ab06fc and Morisaki et al. PRD 108, 123040 (2023) doi:10.1103/PhysRevD.108.123040 View this GCN Circular online at https://gcn.nasa.gov/circulars/42375. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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