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[vsnet-grb-info 40420] Swift GRB 251018A: Global MASTER-Net observations report
by GCN Circulars 17 Oct '25

17 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42344 SUBJECT: Swift GRB 251018A: Global MASTER-Net observations report DATE: 25/10/18 03:28:45 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-OAFA robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Argentina (OAFA observatory of San Juan National University) was pointed to the Swift GRB 251018A ( R. Gupta et al., GCN 42343) errorbox 105 sec after notice time and 141 sec after trigger time at 2025-10-18 03:14:24 UT, with upper limit up to 18.4 mag. The observations began at zenith distance = 68 deg. The sun altitude is -46.5 deg. The galactic latitude b = -16 deg., longitude l = 359 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3017251 We obtain a following upper limits. Tmid-T0 | Site |Filt.| Expt. | Limit| Comment _________|_____________________|_____|_______|______|________ 147 | MASTER-OAFA | C | 10 | 17.8 | 168 | MASTER-OAFA | C | 20 | 18.3 | 194 | MASTER-OAFA | C | 20 | 18.2 | 225 | MASTER-OAFA | C | 30 | 18.4 | 263 | MASTER-OAFA | C | 30 | 18.4 | 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/42344. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40419] GRB 251018A: Swift detection of a burst with an optical counterpart
by GCN Circulars 17 Oct '25

17 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42343 SUBJECT: GRB 251018A: Swift detection of a burst with an optical counterpart DATE: 25/10/18 03:25:45 GMT FROM: David Palmer at LANL <palmer(a)lanl.gov> R. Gupta (NASA GSFC), R. Brivio (INAF-OAB), S. Dichiara (PSU), M. Ferro (INAF-OAB), D. M. Palmer (LANL), T. Sbarrato (INAF-OAB) and M. H. Siegel (PSU) report on behalf of the Neil Gehrels Swift Observatory Team: At 03:12:02 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 251018A (trigger=1405083). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 282.071, -37.028 which is RA(J2000) = 18h 48m 17s Dec(J2000) = -37d 01' 41" 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 60 sec. The peak count rate was ~2000 counts/sec (15-350 keV), at ~1 sec after the trigger. The XRT began observing the field at 03:13:16.7 UT, 74.4 seconds after the BAT trigger. XRT found a bright, uncatalogued X-ray source located at RA, Dec 282.0433, -37.0265 which is equivalent to: RA(J2000) = 18h 48m 10.39s Dec(J2000) = -37d 01' 35.4" with an uncertainty of 6.3 arcseconds (radius, 90% containment). This location is 79 arcseconds from the BAT onboard position, within the BAT error circle. The initial flux in the 2.5 s image was 5.19e-10 erg cm^-2 s^-1 (0.2-10 keV). UVOT took a finding chart exposure of 150 seconds with the White filter starting 83 seconds after the BAT trigger. There is a candidate afterglow in the rapidly available 2.7'x2.7' sub-image at RA(J2000) = 18:48:10.04 = 282.04183 DEC(J2000) = -37:01:42.2 = -37.02840 with a 90%-confidence error radius of about 0.62 arc sec. This position is 8.0 arc sec. from the center of the XRT error circle. The estimated magnitude is 17.96 with a 1-sigma error of about 0.15. No correction has been made for the expected extinction corresponding to E(B-V) of 0.100. 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/42343. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40418] GRB 251018A: Fermi GBM Final Real-time Localization
by GCN Circulars 17 Oct '25

17 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42342 SUBJECT: GRB 251018A: Fermi GBM Final Real-time Localization DATE: 25/10/18 03:19:29 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 03:12:00 UT on 18 Oct 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251018A (trigger 782449925.633958 / 251018133). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 294.7, Dec = -40.3 (J2000 degrees, equivalent to J2000 19h 38m, -40d 17'), with a statistical uncertainty of 6.8 degrees. The angle from the Fermi LAT boresight is 36.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251018133/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251018133/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251018133/… View this GCN Circular online at https://gcn.nasa.gov/circulars/42342. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40417] GRB 251017A: SVOM/VT optical observation
by GCN Circulars 17 Oct '25

17 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42341 SUBJECT: GRB 251017A: SVOM/VT optical observation DATE: 25/10/18 02:40:22 GMT FROM: Liping Xin at NAOC, SVOM <xlp(a)nao.cas.cn> L. P. Xin, H. L. Li, Y. N. Ma, Z. H. Yao, Y. L. Qiu, C. Wu, 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/VT performed a Target of Opportunity observation of GRB 251017A detected by Swift/BAT (Gupta et al., GCN 42322) and Glowbug (Woolf et al., GCN 42335;), starting at 2025-10-17T09:17:19 UTC, 37 min after the trigger, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. The optical counterpart (Perez-Garcia et al., GCN 42323; Antier et al., GCN 42325; Goad et al., GCN 42326; Sasada et al., GCN 42329; Lipunov et al., GCN 42330; Fu et al., GCN 42331; Mo et al., GCN 42336, Adami et al. GCN 42339) is detected in both channels. Mid-time | exposure time (s) | band | Magnitude (AB) ---------|-------------------|------|----------------- 3.96 h | 27*70 | VT_B | 22.57+/-0.14 3.96 h | 27*70 | VT_R | 20.30+/-0.05 Given the red color from the VT data, it is likely a medium/high redshift burst with a redshift > 4. Our photometry was in AB magnitude and 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 Centre 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/42341. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40416] GRB 251011A: Fermi GBM Observation
by GCN Circulars 17 Oct '25

17 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42340 SUBJECT: GRB 251011A: Fermi GBM Observation DATE: 25/10/18 02:27:15 GMT FROM: rhamburg(a)usra.edu R. Hamburg (USRA) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 03:41:40.09 UT on 11 October 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251011A (trigger 781846905/251011154), which was also detected by AstroSat (Tembhurnikar et al. 2025, GCN 42199), Insight-HMXT (Wang et al. 2025, GCN 42210), and Swift-BAT/GUANO (DeLaunay et al. 2025, GCN 42245). The Fermi GBM on-ground location is consistent with the Swift position. The angle from the Fermi LAT boresight is 62 degrees. The GBM light curve consists of a multi-peaked structure with a duration (T90) of about 4.9 s (50-300 keV). The time-averaged spectrum from T0-0.7 to T0+4.9 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -0.76 +/- 0.01 and the cutoff energy, parameterized as Epeak, is 136 +/- 1 keV. The event fluence (10-1000 keV) in this time interval is (3.26 +/- 0.07)E-06 ergs/cm^2 erg/cm^2. The 1-sec peak photon flux measured starting from T0+1.8 s in the 10-1000 keV band is 11.5 +/- 0.3 ph/s/cm^2. A Band function fits the spectrum equally well with Epeak = 125 +/- 1 keV, alpha = -0.69 +/- 0.01 and beta = -2.70 +/- 0.04. 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/42340. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40415] GRB 251017A: OHP/T193 i-band observations
by GCN Circulars 17 Oct '25

17 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42339 SUBJECT: GRB 251017A: OHP/T193 i-band observations DATE: 25/10/17 22:08:45 GMT FROM: Christophe Adami at LAM <christophe.adami(a)lam.fr> C. Adami (LAM/Pytheas/AMU), N.A. Rakotondrainibe (LAM), E. Le Floc'h (CEA/Irfu), S. Basa (Pytheas/OHP/LAM), B. Schneider (LAM), report on behalf of the MISTRAL GRB collaboration: We carried out observations of the GRB 251017A (Gupta et al., GCN 42322; Perez-Garcia et al., GCN 42323; Antier et al., GCN 42325; Goad et al., GCN 42326; Sasada et al., GCN 42329; Lipunov et al., GCN 42330; Fu et al., GCN 42331; Woolf et al., GCN 42335; Mo et al., GCN 42336) using the T193cm telescope at Observatoire de Haute-Provence (France) equipped with the MISTRAL spectro-imager. We obtained 3 exposures of 3min and 2 exposures of 10min in the i-band at a mid time of 2025-10-17 19:52:19UT, corresponding to T-T0 = 11.19 hr. The afterglow is detected and we measured the following preliminary magnitude: i’ = 21.39+/-0.32 mag (AB) The photometric calibration was performed using nearby stars from the PanSTARRS catalog and the magnitudes are not corrected for Galactic extinction. We used the STDWeb/STDPipe tools (Karpov 2025). We acknowledge the excellent support from the Observatoire de Haute-Provence and in particular Yoann Degot-longhi and the SOPHIE observers H. Bouy View this GCN Circular online at https://gcn.nasa.gov/circulars/42339. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40414] GRB 251013C: OHP/T193 third epoch optical observations and detected rebrightening
by GCN Circulars 17 Oct '25

17 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42338 SUBJECT: GRB 251013C: OHP/T193 third epoch optical observations and detected rebrightening DATE: 25/10/17 21:44:41 GMT FROM: Christophe Adami at LAM <christophe.adami(a)lam.fr> C. Adami (LAM/Pytheas/AMU), N.A. Rakotondrainibe (LAM), E. Le Floc'h (CEA/Irfu), S. Basa (Pytheas/OHP/LAM), B. Schneider (LAM), report on behalf of the MISTRAL GRB collaboration: We carried out further observations of the GRB 251013C optical, NIR, and radio afterglow (Palmerio et al., GCN 42223 ; Perez-Garcia et al., GCN 42225 ; Konno et al., GCN 42226 ; Martin-Carrillo et al., GCN 42227 ; Masi et al., GCN 42228 ; Palmerio et al., GCN 42229 ; Moskvitin et al., GCN 42230 ; Gompertz et al., GCN 42231 ; Lipunov et al., GCN 42235 ; Garnavich, GCN42240; Watson et al., GCN 42241 ; Lopez-Camara et al., GCN 42242 ; Laskar et al., GCN 42243; Zhang et al., GCN 42248; Brosio et al., GCN 42251; Reguitti et al., GCN 42253 ; Quintana-Ansaldo et al., GCN 42254; Maksut et al., GCN 42256; Ghosh et al., GCN 42261 ; Quadri et al., GCN 42262 ; Adami et al. GCN 42266 ; Peretto et al., GCN 42267 ; Ruocco et al., GCN 42269 ; Calapai, GCN 42275; Adami et al., GCN 42276; Globus et al., GCN 42279; Abidkhanov et al., 42283; Rhodes et al., GCN 42294; Siegel et al., GCN 42298; Leonini et al., GCN 42301; Christy et al., GCN 42312; Moreno Méndez et al., GCN 42318; He et al., GCN 42319; Pavoni et al., GCN 42333; Bochenek et al., GCN 42334) using the T193cm telescope at Observatoire de Haute-Provence (France) equipped with the MISTRAL spectro-imager. We obtained 4 exposures of 10min in the r-band at a mid time of 2025-10-17 19:05:33UT, corresponding to T-T0 = 97.43 hr. The afterglow is well detected and we measured the following preliminary magnitude: r’ = 20.74+/-0.06 mag (AB) This clearly shows a rebrightening as compared to our second epoch observations (r’ = 21.29 +/- 0.07), consistently with the results of Moreno Méndez et al. (GCN 42318). The photometric calibration was performed using nearby stars from the PanSTARRS catalog and the magnitudes are not corrected for Galactic extinction. We used the STDWeb/STDPipe tools (Karpov 2025). We acknowledge the excellent support from the Observatoire de Haute-Provence and in particular Yoann Degot-longhi and the SOPHIE observers H. Bouy View this GCN Circular online at https://gcn.nasa.gov/circulars/42338. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40413] LIGO/Virgo/KAGRA S251017di: Retraction of GW compact binary merger candidate
by GCN Circulars 17 Oct '25

17 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42337 SUBJECT: LIGO/Virgo/KAGRA S251017di: Retraction of GW compact binary merger candidate DATE: 25/10/17 21:38:45 GMT FROM: shoki.iwaguchi(a)ligo.org The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration report: The trigger S251017di is no longer considered to be a candidate of interest. This candidate was initially identified by one or more early-warning analyses by matching partial signal templates to the data. Analysis of additional data up to the putative merger time, with full signal templates, did not make a significant detection, indicating that the initial candidate was likely due to transient noise. View this GCN Circular online at https://gcn.nasa.gov/circulars/42337. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40412] GRB 251017A: J-band detection with WINTER
by GCN Circulars 17 Oct '25

17 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42336 SUBJECT: GRB 251017A: J-band detection with WINTER DATE: 25/10/17 21:17:36 GMT FROM: Geoffrey Mo at Caltech / Carnegie Observatories <gmo(a)mit.edu> Geoffrey Mo (Caltech/Carnegie), Tomas Ahumada (Caltech), Viraj Karambelkar (Columbia), Benjamin Schneider (LAM), Robert Stein (UMD), Danielle Frostig (CfA), Nathan Lourie (MIT), Robert Simcoe (MIT), and Mansi Kasliwal (Caltech) report: We observed the field of GRB 251017A (Gupta et al., GCN 42322; Goad et al., GCN 42326; Woolf et al., GCN 42335) in the near-infrared J band with the Palomar 1-m telescope, equipped with the 1.2-square degree WINTER camera (Lourie et al. 2020, Frostig et al. 2024). Observations began at 2025-10-17T09:01:23 UTC in the J band (~21 minutes after the GRB trigger), consisting of 15 x 120 s exposures. The images were processed using the WINTER data reduction pipeline implemented with mirar (https://github.com/winter-telescope/mirar, https://doi.org/10.5281/zenodo.13352565) We detect a clear source at the optical counterpart location (Gupta et al., GCN 42322; Perez-Garcia et al., GCN 42323; Antier et al., GCN 42325; Sasada et al., GCN 42329; Lipunov et al., GCN 42330; Fu et al., GCN 42331), with magnitude J ~ 18.7 mag (AB). WINTER (Wide-field INfrared Transient ExploreR) is a partnership between MIT and Caltech, housed at Palomar Observatory, and funded by NSF MRI, NSF AAG, the David and Lucile Packard Foundation, and the MIT Kavli Institute for Astrophysics and Space Research. View this GCN Circular online at https://gcn.nasa.gov/circulars/42336. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40411] GRB 251017A: Glowbug gamma-ray detection
by GCN Circulars 17 Oct '25

17 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42335 SUBJECT: GRB 251017A: Glowbug gamma-ray detection DATE: 25/10/17 21:06:38 GMT FROM: richard.s.woolf.civ(a)us.navy.mil R. Woolf, C.C. Cheung, 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 251017A, which was also detected by Swift/BAT (GCN 42322). Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2025-10-17 08:40:42.816 with a duration of 8.2 s and a total significance of about 11.9 sigma. The light curve comprises two primary peaks. 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 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/42335. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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