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

[vsnet-grb-info 40484] GRB 251023B: Glowbug gamma-ray detection
by GCN Circulars 23 Oct '25

23 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42407 SUBJECT: GRB 251023B: Glowbug gamma-ray detection DATE: 25/10/23 19:43:30 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 251023B, which was also detected by MAXI (as MAXI J0451+122; GCN 42392) and CALET (GCN 42402), and possibly associated with the Einstein Probe/WXT-detected source EP#01709247298 (GCN 42401). Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2025-10-23 08:48:53.664 with a duration of 7.9 s and a total significance of about 7.0 sigma. The onset measured by Glowbug is 9.4 s prior to the MAXI-reported T0. The Glowbug light curve is dominated by a single peak corresponding to the maximum in the CALET light curve (GCN 42402). 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/42407. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40483] EP251023a: ULL-ASTRO-MASTER detection of the optical afterglow with LCO 40-cm telescope at Teide Observatory
by GCN Circulars 23 Oct '25

23 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42406 SUBJECT: EP251023a: ULL-ASTRO-MASTER detection of the optical afterglow with LCO 40-cm telescope at Teide Observatory DATE: 25/10/23 19:23:09 GMT FROM: Ismael Perez-Fournon at Instituto de Astrofisica de Canarias <ipf(a)iac.es> A. Selezneva, J. Basurto Merino, P.G. Berdayes, A. Caballero-Almagro, A. Cerón, M. Contreras, F. Díaz-Segado, T. Ferrer-Laviña, B. Gandolfi, V. Ghiraldo, J. Hernández Fung, L. Juliá-Maroto, E. Lekaroz-Urriza, M. Manzano García, E. Mejía-Martínez, J. Prieto Polo, M. Pulido-Torres, M. Quintana-Ansaldo, A. Schenone-Zanuzzi, T. Tundidor Rodríguez, E. Urquijo-Rodríguez (all ULL), M. Abdul-Masih (IAC and ULL), and I. Pérez-Fournon (IAC and ULL). Following the detection of the X-ray transient EP251023a by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (ID: 01709247295, Wu et al., GCN circ. 42388), we observed the field with one of the two Las Cumbres Observatory (LCO) 40-cm telescopes (Planewave Delta Rho 350 telescopes equipped with QHY600 CMOS cameras) located at the LCO node at Teide Observatory (Tenerife, Canary Islands, Spain). The observation, a single exposure of 300 sec in the SDSS r filter, started on 2025-10-23 at 06:09:24 UT, about 3.64 hours after the EP-WXT trigger. The optical counterpart detected by GOTO (GOTO25ixt, Wortley et al., GCN circ. 42387) is clearly detected in our image with a magnitude of r = 18.69 +/- 0.10 (AB), calibrated against PanSTARRS-1 DR2 stars and not corrected for galactic extinction, that is consistent with other optical detections at similar epochs (Li et al., GCN circ. 42389; Liu et al., GCN circ. 42391) and brighter than the COLIBRÍ detection at a later epoch (Mandarakas et al., GCN circ. 42400). A redshift of z = 2.232 has been measured by Chornock (GCN circ. 42398) using Keck/LRIS. Based on observations made with the Las Cumbres Observatory’s education network telescopes that were upgraded through generous support from the Gordon and Betty Moore Foundation (LCO program IAC2025B-010). 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/42406. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40482] EP251023a: Global MASTER-Net observations report
by GCN Circulars 23 Oct '25

23 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42405 SUBJECT: EP251023a: Global MASTER-Net observations report DATE: 25/10/23 17:18:38 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) was pointed to the EP251023a ( EP Team et al., GCN 42388) errorbox 27379 sec after notice time and 51442 sec after trigger time at 2025-10-23 16:48:31 UT, with upper limit up to 18.2 mag. The observations began at zenith distance = 80 deg. The sun altitude is -50.5 deg. The galactic latitude b = 31 deg., longitude l = 204 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3021715 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 51472 | 2025-10-23 16:48:31 | MASTER-Tunka | (08h 28m 06.31s , +20d 38m 18.3s) | C | 60 | 18.2 | 51472 | 2025-10-23 16:48:31 | MASTER- | (08h 28m 21.58s , +20d 31m 55.6s) | C | 60 | 18.2 | 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/42405. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40481] GRB 251023B / EP#01709247298: COLIBRÍ optical counterpart candidate
by GCN Circulars 23 Oct '25

23 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42404 SUBJECT: GRB 251023B / EP#01709247298: COLIBRÍ optical counterpart candidate DATE: 25/10/23 16:26:48 GMT FROM: nikos.mandarakas(a)lam.fr Nikos Mandarakas (LAM), Ramandeep Gill (UNAM), Jean-Grégoire Ducoin (CPPM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Rosa L. Becerra (UNAM), Nathaniel R. Butler (ASU) , Damien Dornic (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM): We imaged the field of the GRB 251023B / EP#01709247298, that might be associated with MAXI J0451+122 (Kang et al., GCN Circ. 42392) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2025-10-23 10:14:07 to 11:41:55 UTC (from 1.42 to 2.88 hours after the trigger) and obtained 32 minutes of simultaneous exposure in the r and z filters. The data were reduced and coadded with the COLIBRÍ pipeline and analysed with STDWeb/STDPipe (Karpov 2025). The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction. We detect an uncatalogued source consistent with the XRT 3.7 arcsec error circle (Evans et al., GCN Circ. 42401) at: RA(J2000) = 04:54:00.63 = 73.50263 degrees Dec(J2000) = 12:39:28.4 = 12.65789 degrees with an uncertainty of 0.5 arcsec. The preliminary magnitudes derived for that source is: r = 21.86 +/- 0.04 z = 20.45 +/- 0.04 Further observations are planned. We thank the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir and the COLIBRÍ and DDRAGO engineering teams. COLIBRÍ is an astronomical observatory developed and operated jointly by France (AMU, CNES and CNRS) and Mexico (UNAM and SECIHTI). It is located at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, Mexico. View this GCN Circular online at https://gcn.nasa.gov/circulars/42404. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40480] IPN triangulation of GRB 251016B
by GCN Circulars 23 Oct '25

23 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42403 SUBJECT: IPN triangulation of GRB 251016B DATE: 25/10/23 16:17:46 GMT FROM: Dmitry Svinkin at Ioffe Institute <svinkin(a)mail.ioffe.ru> A.S. Kozyrev, D.V. Golovin, M.L. Litvak, I.G. Mitrofanov, and A.B. Sanin on behalf of the MGNS/BepiColombo and HEND/Mars Odyssey teams, J. Benkhoff on behalf of the BepiColombo team, D. Svinkin, D. Frederiks, A. Lysenko, A. Ridnaia, and T. Cline on behalf of the Konus-Wind team, A. Goldstein, M. S. Briggs, C. Wilson-Hodge, and E. Burns on behalf of the Fermi-GBM team, S. Barthelmy, J. Cummings, H. Krimm, D. Palmer, A. Tohuvavohu, and J. DeLaunay on behalf of the Swift-BAT team, and W. Boynton, C. Fellows, K. Harshman, H. Enos, R. Starr, and A.S. Gardner on on behalf of the GRS-Odyssey GRB team, report: The long-duration GRB 251016B (Ferm-GBM detection: The Fermi GBM team, GCN 42316; Godwin et al., GCN 42383; CALET-GBM detection: Yamaoka et al., GCN 42320; AstroSat-CZTI detection: Harsha et al., GCN 42324) was detected by Fermi (GBM trigger 782351945), CALET (GBM), AstroSat (CZTI), Konus-Wind, Swift (BAT), Mars-Odyssey (HEND), and BepiColombo (MGNS), at about 86340 s UT (23:59:00). The burst was outside the coded field of view of the BAT. We have triangulated it to a preliminary, 3 sigma error box whose coordinates are: --------------------------------------------- RA(2000), deg Dec(2000), deg --------------------------------------------- Center: 180.582 (12h 02m 20s) +57.856 (+57d 51' 21") Corners: 173.603 (11h 34m 25s) +54.048 (+54d 02' 53") 182.331 (12h 09m 19s) +58.703 (+58d 42' 09") 191.445 (12h 45m 47s) +61.827 (+61d 49' 37") 178.988 (11h 55m 57s) +57.018 (+57d 01' 07") --------------------------------------------- The error box area is 2295 sq. arcmin, and its maximum dimension is 12.186 deg (the minimum one is 5 arcmin). The Sun distance was 69 deg. This localization may be improved. A triangulation map and HEALPix FITS file are posted at http://www.ioffe.ru/LEA/GRBs/GRB251016_T86340/IPN/ The HEALPix triangulation map is the multi-order HEALPix in units of probability density. The Konus-Wind time history and spectrum will be given in a forthcoming GCN Circular. View this GCN Circular online at https://gcn.nasa.gov/circulars/42403. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40479] GRB 251023B: CALET Gamma-Ray Burst Monitor detection
by GCN Circulars 23 Oct '25

23 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42402 SUBJECT: GRB 251023B: CALET Gamma-Ray Burst Monitor detection DATE: 25/10/23 16:16:02 GMT FROM: Yuta Kawakubo at Aoyama Gakuin University <kawakubo(a)phys.aoyama.ac.jp> S. Nakahira (JAXA), A. Yoshida, T. Sakamoto, S. Sugita, Y. Kawakubo (AGU), K. Yamaoka (Nagoya U), Y. Asaoka (ICRR), S. Torii, Y. Akaike, K. Kobayashi (Waseda U), Y. Shimizu, T. Tamura (Kanagawa U), N. Cannady (GSFC/UMBC), M. L. Cherry (LSU), S. Ricciarini (U of Florence), P. S. Marrocchesi (U of Siena), and the CALET collaboration: The long GRB 251023B (MAXI/GSC Detection: Kang et al., GCN Circ 42392) was detected in the ground analysis of the CALET Gamma-ray Burst Monitor (CGBM) data around 08:49:03 on 23 October 2025 (referenced to the MAXI detection: GCN Circ. 42392). (https://cgbm.calet.jp/cgbm_trigger/flight/1445244062/index.html). The burst signal was seen by all CGBM detectors. The burst light curve shows a multi-peaked structure that starts at T-31.7 sec and ends at T+8.2 sec. The T90 and T50 durations measured by the HXM2 data are 34.9 +/- 4.2 sec and 16.7 +/- 2.2 sec (7-100 keV), respectively. The ground-processed light curve is available at https://cgbm.calet.jp/cgbm_trigger/ground/1445244062/ The CALET data used in this analysis are provided by the Waseda CALET Operation Center located at Waseda University. View this GCN Circular online at https://gcn.nasa.gov/circulars/42402. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40478] EP#01709247298: Swift-XRT counterpart detection
by GCN Circulars 23 Oct '25

23 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42401 SUBJECT: EP#01709247298: Swift-XRT counterpart detection DATE: 25/10/23 15:35:42 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> P.A. Evans (U. Leicester), J.A. Kennea (PSU), E. Ambrosi (INAF-IASFPA) , A.P. Beardmore (U. Leicester), M.G. Bernardini (INAF-OAB), R. Brivio (INAF-OAB), D.N. Burrows (PSU), S. Campana (INAF-OAB), M. Capalbi (INAF-OAR), A. D'Ai (INAF-IASFPA), P. D'Avanzo (INAF-OAB), V. D'Elia (SSDC & INAF-OAR), S. Dichiara (PSU), M. Ferro (INAF-OAB), A. Melandri (INAF-OAR), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), M. Perri (SSDC & INAF-OAR), C. Salvaggio (INAF-OAB), T. Sbarrato (INAF-OAB), B. Sbarufatti (INAF-OAB), M.A. Williams (PSU) report on behalf of the Swift-XRT team: Swift-XRT has performed follow-up observations of the Einstein Probe/WXT-detected source EP#01709247298, collecting 1.6 ks of Photon Counting (PC) mode data between T0+6.6 ks and T0+8.3 ks after the trigger. A likely counterpart has been found. This source is 43 arcmin from the position of the MAXI-detected transient GRB 251023B / MAXI J0451+122 (Kang et al., GCN Circ. 42392), well outside their error region, thus its association, while likely on temporal grounds, remains unconfirmed. The details of this source are: Source 1 (SWIFT J045400.4+123929): ================================== RA (J2000.0): 73.5018 = 04 54 00.43 Dec (J2000.0): +12.6583 = +12 39 29.9 Error: 3.7 (arcsec, radius, 90% confidence). Detect flag: GOOD Distance: 22 arcsec from the Einstein Probe/WXT position. Mean rate: 0.152 +/- 0.011 ct s^-1 Mean flux: (5.94 +/- 0.44)e-12 erg cm^-2 s^-1 Peak rate: 0.221 +/- 0.049 ct s^-1 Peak flux: (8.6 +/- 1.9)e-12 erg cm^-2 s^-1 ECF: 3.91e-11 erg cm^-2 ct^-1 assuming NH=3.15e+21 cm^-2, gamma=1.97 determined from a spectral fit. XMM UL: 2.3e-12 erg cm^-2 s^-1, (0.3-10 keV) so the source is 3.2-sigma above this 3-sigma upper limit. All fluxes are 0.3-10 keV, observed. For all flux conversions and comparisons with catalogues and upper limits from other missions, we assumed a power-law spectrum with NH=3x10^20 cm^-2 and photon index (Gamma)=1.7 unless otherwise stated. The results of the XRT-team automatic analysis of the XRT observations, including a position-specific upper limit calculator, are available at https://www.swift.ac.uk/EP/EP_FIELD00077. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/42401. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40477] EP251023a: COLIBRÍ optical observations
by GCN Circulars 23 Oct '25

23 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42400 SUBJECT: EP251023a: COLIBRÍ optical observations DATE: 25/10/23 15:22:43 GMT FROM: nikos.mandarakas(a)lam.fr Nikos Mandarakas (LAM), Ramandeep Gill (UNAM), Jean-Grégoire Ducoin (CPPM), Alan M. Watson (UNAM), Noémie Globus (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Rosa L. Becerra (UNAM), Nathaniel R. Butler (ASU) , Damien Dornic (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM): We imaged the field of the EP251023a (Wu et al., GCN Circ. 42388) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2025-10-23 09:29 to 10:57 UTC (from 7.0 to 8.4 hours after the trigger) and obtained 32 minutes of simultaneous exposure in the r and z filters, alternating with other observations. The data were reduced and coadded with the COLIBRÍ pipeline and analysed with STDWeb/STDPipe (Karpov 2025). The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction. We detected the optical counterpart firstly identified by GOTO (Wortley et al., GCN Circ. 42387) and subsequently reported by Las Cumbres Observatory (Li et al., GCN Circ. 42389) and NOT (Liu et al., GCN Circ. 42391) at preliminary magnitudes of: r = 18.82 +/- 0.01 z = 18.52 +/- 0.01 Further observations are planned. We thank the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir and the COLIBRÍ and DDRAGO engineering teams. COLIBRÍ is an astronomical observatory developed and operated jointly by France (AMU, CNES and CNRS) and Mexico (UNAM and SECIHTI). It is located at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, Mexico. View this GCN Circular online at https://gcn.nasa.gov/circulars/42400. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40476] GRB 251013C: further SAO RAS optical observations
by GCN Circulars 23 Oct '25

23 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42399 SUBJECT: GRB 251013C: further SAO RAS optical observations DATE: 25/10/23 14:44:06 GMT FROM: Alexander Moskvitin at SAO RAS <mosk(a)sao.ru> A. S. Moskvitin, O. I. Spiridonova, V. V. Vlasyuk (SAO RAS) report on behalf of GRB follow-up collaboration. 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 on October 20 and 21 nights. The optical afterglow (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; Moskvitin et al., GCN 42230; Gompertz et al., GCN 42231; Lipunov et al., GCN 42235; Garnavich, GCN 42240; Watson et al., GCN 42241; López-Cámara et al., GCN 42242; Brosio et al., GCN 42251; Reguitti, 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., GCNs 42266, 42276, 42338; Peretto et al., GCN 42267; Ruocco et al., GCN 42269; Calapai, GCN 42275; Globus et al., GCN 42279; Evans, GCN 42281; Abidkhanov et al., GCN 42283; Siegel, GCN 42298; Leonini et al, GCN 42301; Méndez et al., GCN 42318; He et al., GCN 42319; Pavoni et al., GCN 42333; Bochenek and Perley, GCN 42334; Volnova et al., GCN 42396) is clearly detected in the stacked images with the following brightness. Date UT start t-T0 Exp. Filter OT Err. UL (mid, d) (s) 2025.10.20 19:59:38 7.12682 13 x 300 Rc 21.61 +/- 0.11 22.7 2025.10.21 17:02:31 8.01103 19 x 300 Rc 21.80 +/- 0.10 23.0 Preliminary photometry is based on the nearby SDSS objects (magnitudes converted with Lupton 2005 equations) and has not corrected for the Galactic extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/42399. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 40475] EP251023a: Keck/LRIS spectroscopic redshift z=2.232
by GCN Circulars 23 Oct '25

23 Oct '25

TITLE: GCN CIRCULAR NUMBER: 42398 SUBJECT: EP251023a: Keck/LRIS spectroscopic redshift z=2.232 DATE: 25/10/23 14:39:53 GMT FROM: Ryan Chornock at UC Berkeley <chornock(a)berkeley.edu> R. Chornock (UC Berkeley) reports: We observed the optical afterglow (Wortley et al., GCN 42387; Li et al., GCN 42389; Liu et al. GCN 42391) of the X-ray transient EP251023a (Wu et al., GCN 42388) using the Low-Resolution Imaging Spectrometer on the Keck-I telescope at a mean time of 13:26UT on 2025 October 23 (~10.9 hours after the EP trigger). Observations covered the range 3100-10300 Angstroms. The afterglow remains bright and the continuum is well detected across the full spectral range. Multiple absorption systems are present, but the highest redshift absorber has many absorption lines (including Lyman-alpha, Si II, Si II*, O I, O I*, C II, Si IV, C IV, Fe II, Mg I and Mg II) present at a common redshift of z=2.232+/-0.001. View this GCN Circular online at https://gcn.nasa.gov/circulars/42398. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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