GCN Circular 45897
Subject
GRB 261011A: GOTO optical counterpart detection
Event
Date
2026-10-11T14:26:21Z (5 hours ago)
From
d.s.oneill@bham.ac.uk
Via
Web form
D. O'Neill,B. P. Gompertz, M. Shrestha, R. Starling, A. Kumar, G. Ramsay, 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 and M. Pursiainen report on behalf of GOTO collaboration:
We report on optical observations with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022, Dyer et al. 2024) in response to the Swift/BAT (Cenko et al. GCN 45896 and SVOM ECLIARS (Huang et al, GCN 45895) alerts for GRB 261011A.
Observations covering the localisation area began at 2026-10-11 13:53:16 UT, (+0.11h post trigger) with an average 5-sigma depth of 21.2 mag.
Images were processed immediately after acquisition using the GOTO pipeline. Difference imaging was performed using deeper template observations. Source candidates were initially filtered using a classifier (Killestein et al. 2021) and cross-matched against a variety of contextual and minor planet catalogs. Human vetting was carried out in real time on any candidates that passed the above checks (Lyman et al. 2026).
We detect the counterpart reported in Cenko et al. GCN 45896.The source was detected with L = 16.32 ± 0.01 AB mag (+0.11h). We find no evidence of the source prior to the GRB trigger time in previous GOTO observations taken at 2026-10-11 13:40:24 (-0.1h) down to a depth of >20.57 AB mag, the ZTF observations provided by the Lasair broker (Smith et al. 2019), or the ATLAS forced photometry server (Shingles et al. 2021).