TITLE: GCN CIRCULAR NUMBER: 42046 SUBJECT: GRB 251001B: Further GOTO observations of optical counterpart. DATE: 25/10/01 20:34:36 GMT FROM: d.s.oneill@bham.ac.uk D. O'Neill, B. P. Gompertz, G. Ramsay, R. Starling, M. Kennedy, B. Godson, J. Lyman, K. Ackley, M. J. Dyer, K. Ulaczyk, A. Kumar,, D. Steeghs, D. K. Galloway, V. Dhillon, P. O'Brien, K. Noysena, R. Kotak, R. P. Breton, L. K. Nuttall, and J. Casares report on behalf of the GOTO collaboration: We report on new observations with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022, Dyer et al. 2024) in response to GRB 251001B (Fermi GBM team, GCN 42038; Beardmore et al. GCN 42039). Following the detection of the optical counterpart of GRB 251001B (Gompertz et al. GCN 42040, An et al. GCN 42041, Strausbaugh & Cucchiara, GCN 42043) we detect the counterpart again in an additional epoch of GOTO L-band (400-700 nm) imaging taken at 2025-10-01 15:44:25 UT (1.45h post-trigger) consisting of 4x90s exposures. We find the counterpart has faded to L=20.6±0.3 AB mag, consistent with a power law decay with index: alpha = -0.75. 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). View this GCN Circular online at https://gcn.nasa.gov/circulars/42046. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...