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GCN Circular 35596

GRB 240122A: GOTO optical counterpart candidate
2024-01-22T18:50:31Z (5 months ago)
Amit Kumar at University of Warwick, UK <>
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A. Kumar; B. P. Gompertz; K. Ackley; G. Ramsay; R. Starling; M. J. Dyer; J. Lyman; K. Ulaczyk; F. Jimenez-Ibarra; D. O'Neill; D. Steeghs; D. K. Galloway; V. Dhillon; P. O'Brien; K. Noysena; R. Kotak; R. P. Breton; L. K. Nuttall; E. Pall'e and D. Pollacco report on behalf of the GOTO collaboration:

The Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022) serendipitously covered the localisation region of MAXI/GSC detected GRB 240122A (Negoro et al. GCN 35593) at 11:11:43 UT on 2024-01-22 (43.6 minutes after trigger). Each 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 recent survey 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 1 new optical transient (GOTO24eu/AT2024apy) within the MAXI/GSC uncertainty region. We find no evidence of this source prior to the GRB trigger time in the previous GOTO epoch at 2024-01-21 12:06:42 (22.4 hours prior), to a 5 sigma limiting magnitude of L > 19.8. The source was also not present in 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) | Filter | Mag(AB)
GOTO24eu/AT2024apy | 06:12:12.91| -19:08:38.81 | L | 17.06 +/- 0.04

Magnitudes were calibrated using ATLAS-REFCAT2 (Tonry et al. 2018) and are not corrected for Galactic extinction.

Observations are ongoing.
GOTO ( 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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