TITLE: GCN CIRCULAR NUMBER: 40215 SUBJECT: SVOM/sb25042207: GOTO optical upper limits DATE: 25/04/23 06:57:54 GMT FROM: Sergey Belkin at Monash University sergey.belkin@monash.edu
S. Belkin, A. Kumar, G. Ramsay, B. P. Gompertz, R. Starling, K. Ackley, M. J. Dyer, J. Lyman, K. Ulaczyk, D. O'Neill, B. Godson, 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 optical observations with the Gravitational-wave Optical Transient Observer (GOTO, Steeghs et al. 2022; Dyer et al. 2024) in response to the SVOM/ECLAIRs alert sb25042207 (Liang et al., GCN 40213). Targeted observations were performed on April 22 2025 23:39:55 UT (+1.06 h post trigger) and on April 23 2025 01:20:48 UT (+2.74 h post trigger). The first epoch of observations consisted of 4x90 s exposures, while the second epoch was obtained in survey mode with 4x45 s exposures. All images were taken 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. 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.
No new transients that could be credibly associated with SVOM/ECLAIRs sb25042207 were detected down to a 5-sigma L-band limiting magnitude of 20.4.
Additionally, no source is detected prior to the GRB trigger time in archival GOTO observations (4x45 s; in survey mode) taken 1.347 h before the trigger, down to a 5-sigma L-band upper limit of 19.7 mag.
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).
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