GCN Circular 42543
Subject
GRB 251103A: GOTO optical afterglow detection
Event
Date
2025-11-03T09:46:24Z (2 days ago)
From
Sergey Belkin at Monash University <sergey.belkin@monash.edu>
Via
Web form
D. O'Neill, S. Belkin, B. P. Gompertz, G. Ramsay, R. Starling, K. Ackley, M. Dyer, J. Lyman, K. Ulaczyk, D. Steeghs, D. Galloway, V. Dhillon, P. O'Brien, K. Noysena, R. Kotak, R. Breton, J. Casares, L. Nuttall, B. Godson, T. Killestein, A. Kumar and M. Pursiainen report on behalf of the GOTO collaboration:
We report on optical observations with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022, Dyer et al. 2024) of GRB 251103A (Hu et al., GCN 42534; Fermi GBM Team, GCN 42536).
A serendipitous image from the all-sky survey was taken on Nov. 3 2025 06:15:34 UT (+1.5h post trigger). The observation consisted of 4x45s exposures in the GOTO L-band (400-700 nm). Images were processed immediately after acquisition using the GOTO pipeline. Difference imaging was performed using deeper template observations.
We detect the optical counterpart (Schneider et al., GCN 42535; Turpin et al., GCN 42538; Gritsevich et al., GCN 42539; Izzo et al., GCN 42540) with an AB magnitude of L = 17.81 ± 0.03.
Magnitudes were calibrated using ATLAS-REFCAT2 (Tonry et al. 2018) and are not corrected for Galactic extinction.
GOTO (https://goto-observatory.org) is a network of telescopes that is principally funded by the STFC and operated at the Roque de los Muchachos Observatory on La Palma, Spain, and Siding Spring Observatory in NSW, Australia, on behalf of a consortium including the University of Warwick, Monash University, Armagh Observatory & Planetarium, the University of Leicester, the University of Sheffield, the National Astronomical Research Institute of Thailand (NARIT), the University of Turku, the University of Portsmouth, the University of Manchester and the Instituto de Astrofisica de Canarias (IAC).