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[vsnet-grb-info 40530] GRB 251025B: ULL-ASTRO-MASTER optical counterpart detection with IAC80 telescope at Teide Observatory
by GCN Circulars 26 Oct '25

26 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42450 SUBJECT: GRB 251025B: ULL-ASTRO-MASTER optical counterpart detection with IAC80 telescope at Teide Observatory DATE: 25/10/26 03:31:47 GMT FROM: Ismael Perez-Fournon at Instituto de Astrofisica de Canarias <ipf(a)iac.es> J. Hernández Fung, P.G. Berdayes, M. Contreras, B. Gandolfi, L. Juliá-Maroto, A. Schenone-Zanuzzi, E. Urquijo-Rodríguez, J. Basurto Merino, A. Caballero-Almagro, A. Cerón, F. Díaz-Segado, T. Ferrer-Laviña, V. Ghiraldo, E. Lekaroz-Urriza, M. Manzano García, E. Mejía-Martínez, J. Prieto Polo, M. Pulido-Torres, M. Quintana-Ansaldo, A. Selezneva, T. Tundidor Rodríguez (all ULL), M. Abdul-Masih (IAC and ULL), and I. Pérez-Fournon (IAC and ULL). Following the detection of GRB 251025B (sb25102502) by SVOM (Hussein et al., GCN circ. 42437), we observed the field with the IAC80 telescope equipped with the CAMELOT2 camera at Teide Observatory (Tenerife, Canary Islands, Spain). The observation, a single exposure of 300 sec in the SDSS g' filter, started on 2025-10-26 at 00:50:31 UT, about 10.44 hours after the SVOM trigger. The optical counterpart detected by Wu et al. (GCN circ. 42438), Gress et al. (GCN circ. 42439), Wu et al. (GCN circ. 42440), and Mohan et al. (GCN circ. 42447) is clearly detected in our image with a magnitude of g = 20.37 +/- 0.12 (AB), calibrated against PanSTARRS-1 DR2 stars and not corrected for galactic extinction. The optical counterpart position is consistent within the errors with the position of the X-ray afterglow measured by Swift-XRT (Beardmore et al. GCN circ. 42445). This work is based on observations made with the IAC80 telescope operated on the island of Tenerife by the Instituto de Astrofísica de Canarias in the Spanish Observatorio del Teide. We acknowledge the expert assistance of Roberto C. Álvarez and Borja Castañeda. These observations are part of a course in Astrophysical Techniques of the Master in Astrophysics of the Astrophysics Department of the University of La Laguna in collaboration with the Instituto de Astrofísica de Canarias (La Laguna, Tenerife, Canary Islands, Spain). This work made use of the Astro-COLIBRI platform (P. Reichherzer et al. 2021, ApJS, 256, 5). View this GCN Circular online at https://gcn.nasa.gov/circulars/42450. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40529] GRB 251025C: Fermi GBM Final Real-time Localization
by GCN Circulars 25 Oct '25

25 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42449 SUBJECT: GRB 251025C: Fermi GBM Final Real-time Localization DATE: 25/10/25 23:19:13 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 23:08:40 UT on 25 Oct 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251025C (trigger 783126525.293544 / 251025964). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 170.7, Dec = 54.9 (J2000 degrees, equivalent to J2000 11h 22m, 54d 53'), with a statistical uncertainty of 2.2 degrees. The angle from the Fermi LAT boresight is 103.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251025964/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251025964/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251025964/… View this GCN Circular online at https://gcn.nasa.gov/circulars/42449. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40528] Konus-Wind detection of GRB 251016B
by GCN Circulars 25 Oct '25

25 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42448 SUBJECT: Konus-Wind detection of GRB 251016B DATE: 25/10/25 20:36:05 GMT FROM: Anna Ridnaia at Ioffe Institute <ridnaia(a)mail.ioffe.ru> A. Ridnaia, D. Frederiks, A. Lysenko, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report: The long-duration GRB 251016B (Ferm-GBM detection: The Fermi GBM team, GCN 42316; Godwin and Meegan, GCN 42383; CALET-GBM detection: Yamaoka et al., GCN 42320; AstroSat-CZTI detection: Harsha et al., GCN 42324; IPN triangulation: Kozyrev et al., GCN 42403) triggered Konus-Wind at T0=86340.495 s UT (23:59:00.495). The burst light curve shows a single pulse which starts at ~T0-0.5 s and has a total duration of ~18.5 s. The emission is seen up to ~6 MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB251016_T86340/ As observed by Konus-Wind, the burst had a fluence of 3.50(-0.18,+0.18)x10^-5 erg/cm2, and a 64-ms peak flux, measured from T0+2.320 s, of 1.22(-0.11,+0.11)x10^-5 erg/cm2/s (both in the 20 keV - 10 MeV energy range). The time-averaged spectrum of the burst (measured from T0 to T0+11.520 s) is best fit in the 20 keV - 10 MeV range by the GRB (Band) model with the following parameters: the low-energy photon index alpha = -0.98(-0.06,+0.06), the high energy photon index beta = -2.29(-0.10,+0.08), the peak energy Ep = 226(-18,+19) keV (chi2 = 93/85 dof). The spectrum near the maximum count rate (measured from T0+0.256 to T0+3.328 s) is best fit in the 20 keV - 10 MeV range by the GRB (Band) model with the following parameters: the low-energy photon index alpha = -0.85(-0.05,+0.06), the high energy photon index beta = -2.41(-0.11,+0.09), the peak energy Ep = 294(-21,+21) keV (chi2 = 67/67 dof). All the quoted errors are at the 68% confidence level. All the quoted values are preliminary. View this GCN Circular online at https://gcn.nasa.gov/circulars/42448. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40527] GRB 251025B: GROWTH-India Telescope optical observations
by GCN Circulars 25 Oct '25

25 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42447 SUBJECT: GRB 251025B: GROWTH-India Telescope optical observations DATE: 25/10/25 20:34:06 GMT FROM: V. Swain at IIT Bombay <vishwajeet.s(a)iitb.ac.in> T. Mohan, V. Swain, S. Patil, A.P. Saikia, V. Bhalerao (IITB), G.C. Anupama, S. Barway (IIA) and K. Angail (IAO) report on behalf of the GIT team: We observed the field of SVOM GRB 251025B (Hussein et al., GCN 42437), with 0.7m GROWTH-India Telescope (GIT). We started the observation at 2025-10-25 15:47:08 UT, i.e., 1.38 hours after the SVOM trigger. Multiple exposures were obtained in the r′-filter, and we detect the optical counterpart in our stacked image. The photometry result follows as: | MJD (mid) | tmid - t0 (hours) | Filter | Exposure (s) | Magnitude (AB) | | --------- | ----------------- | ------ | ------------ | -------------- | |60973.68833| 2.12 | r' | 4 x 360 | 20.41 +- 0.11 | The measurement is calibrated against PanSTARRS DR1 (Chambers et al., 2016) and not corrected for Galactic extinction. Our result is consistent with other optical observations (WU et al., GCN 42438; Gress et al., GCN 42439; Wu et al., GCN 42440). Further multiband optical observations are ongoing. The GROWTH India Telescope (GIT; Kumar et al. 2022) is a 70-cm telescope with a 0.7-degree field of view, set up by the Indian Institute of Astrophysics (IIA) and the Indian Institute of Technology Bombay (IITB) with funding from DST-SERB and IUSSTF. It is located at the Indian Astronomical Observatory (Hanle), operated by IIA. We acknowledge funding by the IITB alumni batch of 1994, which partially supports the operations of the telescope. Telescope technical details are available at https://sites.google.com/view/growthindia/. View this GCN Circular online at https://gcn.nasa.gov/circulars/42447. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40526] GRB 251025B: GROWTH-India Telescope optical observations
by GCN Circulars 25 Oct '25

25 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42447 SUBJECT: GRB 251025B: GROWTH-India Telescope optical observations DATE: 25/10/25 20:34:06 GMT FROM: V. Swain at IIT Bombay <vishwajeet.s(a)iitb.ac.in> T. Mohan, V. Swain, S. Patil, A.P. Saikia, V. Bhalerao (IITB), G.C. Anupama, S. Barway (IIA) and K. Angail (IAO) report on behalf of the GIT team: We observed the field of SVOM GRB 251025B (Hussein et al., GCN 42437), with 0.7m GROWTH-India Telescope (GIT). We started the observation at 2025-10-25 15:47:08 UT, i.e., 1.38 hours after the SVOM trigger. Multiple exposures were obtained in the r′-filter, and we detect the optical counterpart in our stacked image. The photometry result follows as: | MJD (mid) | tmid - t0 (hours) | Filter | Exposure (s) | Magnitude (AB) | | --------- | ----------------- | ------ | ------------ | -------------- | |60973.68833| 2.12 | r' | 4 x 360 | 20.41 +- 0.11 | The measurement is calibrated against PanSTARRS DR1 (Chambers et al., 2016) and not corrected for Galactic extinction. Our result is consistent with other optical observations (WU et al., GCN 42438; Gress et al., GCN 42439; Wu et al., GCN 42440). Further multiband optical observations are ongoing. The GROWTH India Telescope (GIT; Kumar et al. 2022) is a 70-cm telescope with a 0.7-degree field of view, set up by the Indian Institute of Astrophysics (IIA) and the Indian Institute of Technology Bombay (IITB) with funding from DST-SERB and IUSSTF. It is located at the Indian Astronomical Observatory (Hanle), operated by IIA. We acknowledge funding by the IITB alumni batch of 1994, which partially supports the operations of the telescope. Telescope technical details are available at https://sites.google.com/view/growthindia/. View this GCN Circular online at https://gcn.nasa.gov/circulars/42447. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40525] GRB 251024A: Swift/UVOT Upper Limits
by GCN Circulars 25 Oct '25

25 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42446 SUBJECT: GRB 251024A: Swift/UVOT Upper Limits DATE: 25/10/25 20:11:36 GMT FROM: Mike Siegel at PSU/Swift MOC <mhs18(a)psu.edu> M. H. Siegel and M. J. Moss (GSFC) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 251024A 132 s after the BAT trigger (Moss et al., GCN Circ. 42426). No optical afterglow consistent with the XRT position (Beardmore et al., GCN Circ. 42430) is detected in the initial UVOT exposures. Preliminary 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first finding chart (FC) exposure and subsequent exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag white_FC 132 282 147 >21.0 u_FC 290 540 246 >19.9 white 132 591 167 >21.0 v 622 641 19 >18.0 b 547 567 20 >19.8 u 290 540 246 >19.9 w2 597 617 20 >19.2 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.044 in the direction of the burst (Schlegel et al. 1998). View this GCN Circular online at https://gcn.nasa.gov/circulars/42446. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40524] GRB 251025B: Swift-XRT afterglow detection
by GCN Circulars 25 Oct '25

25 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42445 SUBJECT: GRB 251025B: Swift-XRT afterglow detection DATE: 25/10/25 19:52:19 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> A.P. Beardmore (U. Leicester), J.P. Osborne (U. Leicester), B. Sbarufatti (INAF-OAB), C. Salvaggio (INAF-OAB), M. Ferro (INAF-OAB), J.A. Kennea (PSU), D.N. Burrows (PSU), S. Lanava (PSU) and P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team: Swift-XRT has performed follow-up observations of GRB 251025B. We searched for X-ray sources in 1.7 ks of Photon Counting (PC) mode data obtained between T0+2.8 ks and T0+4.5 ks. An uncatalogued X-ray source is detected within the estimated 3-sigma SVOM/ECLAIRs error region (473 arcsec) and is above the RASS 3-sigma upper limit at this position, and is therefore likely the GRB afterglow. Using 1712 s of PC mode data and 1 UVOT image, we find an enhanced XRT position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 29.53107, +30.30373 which is equivalent to: RA (J2000): 01h 58m 07.46s Dec(J2000): +30d 18' 13.4" with an uncertainty of 2.7 arcsec (radius, 90% confidence). This source is 1.25 arcsec from the SVOM/C-GFT position (Wu et al., GCN Circ. 42438) and 37 arcsec from the SVOM/MXT position (Hussein et al., GCN Circ. 42437). At present, the X-ray source shows no evidence of fading. A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.00 (+0.27, -0.25). The best-fitting absorption column is 1.9 (+0.9, -0.8) x 10^21 cm^-2, in excess of the Galactic value of 5.6 x 10^20 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.5 x 10^-11 (4.8 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 1.9 (+0.9, -0.8) x 10^21 cm^-2 Galactic foreground: 5.6 x 10^20 cm^-2 Excess significance: 2.8 sigma Photon index: 2.00 (+0.27, -0.25) The results of the XRT-team automatic analysis are available at https://www.swift.ac.uk/xrt_products/03000153. The results of the full analysis of the XRT observations are available at https://www.swift.ac.uk/SVOM/SVOM_FIELD00044. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/42445. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40523] GRB 251024A: Swift-BAT refined analysis
by GCN Circulars 25 Oct '25

25 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42444 SUBJECT: GRB 251024A: Swift-BAT refined analysis DATE: 25/10/25 19:40:31 GMT FROM: Amy <yarleen(a)gmail.com> T. Sakamoto (AGU), S. D. Barthelmy (GSFC), R. Gupta (GSFC), H. A. Krimm (NSF), S. Laha (GSFC/UMBC), A. Y. Lien (U Tampa), C. B. Markwardt (GSFC), M. J. Moss (GSFC), D. M. Palmer (LANL), T. Parsotan (GSFC), D. Sadaula (GSFC/UMBC) (i.e. the Swift-BAT team): Using the data set from T-240 to T+613 sec from the recent telemetry downlink, we report further analysis of BAT GRB 251024A (trigger #1406589) (Moss et al., GCN Circ. 42426). The BAT ground-calculated position is RA, Dec = 306.666, -68.576 deg which is RA(J2000) = 20h 26m 39.7s Dec(J2000) = -68d 34' 34.3" with an uncertainty of 2.4 arcmin, (radius, sys+stat, 90% containment). The partial coding was 84%. The mask-weighted light curve shows a weak pulse structure that starts at ~T+1 s and peaks at ~T+3 s. The main pulse structure ends at ~T+25 s, and there are some tail emissions that last till ~T+100 s. T90 (15-350 keV) is 82.66 +- 23.27 sec (estimated error including systematics). The time-averaged spectrum from T+1.16 to T+97.28 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.68 +- 0.30. The fluence in the 15-150 keV band is 6.5 +- 1.2 x 10^-07 erg/cm2. The 1-sec peak photon flux measured from T+2.16 sec in the 15-150 keV band is 0.5 +- 0.2 ph/cm2/sec. All the quoted errors are at the 90% confidence level. The results of the batgrbproduct analysis are available at https://swift.gsfc.nasa.gov/results/batgrbcat/BAT_refined_circular/1406589 View this GCN Circular online at https://gcn.nasa.gov/circulars/42444. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40522] IceCube Alert 251025.57: Global MASTER-Net observations report
by GCN Circulars 25 Oct '25

25 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42443 SUBJECT: IceCube Alert 251025.57: Global MASTER-Net observations report DATE: 25/10/25 19:39:23 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) started inspect of the IceCube Alert 251025.57 (trigger No 18513107,09h 42m 47.28s , +15d 19m 48.0s, R=1.19) errorbox 16456 sec after notice time and 16501 sec after trigger time at 2025-10-25 18:22:54 UT, with upper limit up to 17.6 mag. The observations began at zenith distance = 80 deg. The sun altitude is -47.0 deg. The galactic latitude b = 45 deg., longitude l = 219 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3023371 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 16531 | 2025-10-25 18:22:54 | MASTER-Tunka | (09h 42m 13.68s , +14d 52m 14.6s) | C | 60 | 17.6 | 16531 | 2025-10-25 18:22:54 | MASTER- | (09h 42m 26.98s , +14d 45m 50.3s) | C | 60 | 17.3 | 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/42443. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40521] GRB 251024A: Swift-XRT refined Analysis
by GCN Circulars 25 Oct '25

25 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42442 SUBJECT: GRB 251024A: Swift-XRT refined Analysis DATE: 25/10/25 18:09:15 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> S. Dichiara (PSU), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), V. D'Elia (SSDC & INAF-OAR), B. Sbarufatti (INAF-OAB), C. Salvaggio (INAF-OAB), J.A. Kennea (PSU), D.N. Burrows (PSU) and P.A. Evans report on behalf of the Swift-XRT team: We have analysed 4.4 ks of XRT data for GRB 251024A, from 113 s to 56.4 ks after the trigger. The data comprise 30 s in Windowed Timing (WT) mode (the first 10 s were taken while Swift was slewing) with the remainder in Photon Counting (PC) mode. The late-time light curve (from T0+4.5 ks) is consistent with a constant source of mean count rate 4.5e-01 ct/sec. A power-law fit gives an index of -0.14 (+0.15, -0.14). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.06 (+0.16, -0.11). The best-fitting absorption column is consistent with the Galactic value of 3.7 x 10^20 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.2 x 10^-11 (3.6 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 3.7 (+/-2.8) x 10^20 cm^-2 Galactic foreground: 3.7 x 10^20 cm^-2 Excess significance: <1.6 sigma Photon index: 2.06 (+0.16, -0.11) The results of the XRT-team automatic analysis are available at https://www.swift.ac.uk/xrt_products/01406589. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/42442. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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