GCN Circular 37676
Subject
GRB 241002B: GOTO optical counterpart candidate
Date
2024-10-02T11:51:45Z (3 months ago)
From
Amit Kumar at Royal Holloway - U. of London/U. of Warwick, UK <amitkundu515@gmail.com>
Via
Web form
A. Kumar, B. P. Gompertz, D. O'Neill, G. Ramsay, R. Starling, K. Ackley, M. J. Dyer, J. Lyman, K. Ulaczyk, F. Jimenez-Ibarra, D. Steeghs, D. K. Galloway, V. Dhillon, P. O'Brien, K. Noysena, R. Kotak, R. P. Breton, L. K. Nuttall, E. Palle and D. Pollacco report on behalf of the GOTO collaboration:
We report on observations with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022, Dyer et al. 2024) in response to Fermi GBM detected GRB 241002B (Fermi GBM Team, GCN 37668). Targeted observations were performed using the GOTO-South on 2024-10-02 between 09:17:03 and 09:40:00 UT (+3.05h to +3.43h post-trigger, respectively). Each observation consisted of 4x90s exposures in the GOTO L-band (400-700 nm).
56 images were taken across 8 unique pointings, covering 239.8 square degrees within the 90% localisation contour. 79.7% of the total 2D localisation probability was covered, with an average 5-sigma depth of L = 20.3 mag.
Images were processed immediately after acquisition using the GOTO pipeline. Difference imaging was performed using deeper template observations of the same pointings. Source candidates were initially filtered using a classifier (Killestein et al. 2021) and cross-matched against a variety of contextual and minor planet catalogues. Human vetting was carried out in real time on any candidates that passed the above checks.
We identify GOTO24gpc/AT2024xbg as a new candidate optical counterpart within the Fermi GBM 90% localisation region. We find no evidence of this source prior to the GRB trigger time in previous GOTO observations, the ZTF observations provided by the Lasair broker (Smith et al. 2019), or the ATLAS forced photometry server (Shingles et al. 2021).
Name | RA(J2000) | Dec(J2000) | Obs_time | T-T0 (hours) | Filter | Mag (AB) | Lim. Mag
GOTO24gpc / AT2024xbg | 21:53:16.56 | -58:56:51.98 | 2024-10-02 09:17:20 UT | 3.051 | L | 19.53 ± 0.09 | 20.5
We caution that the source position was only covered in a single epoch due to deteriorating weather conditions at Siding Spring. We therefore have no information on the rate of evolution of the transient. GOTO has not covered this position to a depth of at least the discovery magnitude for more than 2 weeks prior to GRB 241002B. Follow-up observations to ascertain the nature of GOTO24gpc / AT2024xbg are encouraged.
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).