TITLE: GCN CIRCULAR NUMBER: 38868 SUBJECT: EP250109a: GOTO optical upper limits DATE: 25/01/09 12:35:49 GMT FROM: Amit Kundu at Royal Holloway - UoL/ U of Warwick, UK amitkundu515@gmail.com
A. Kumar, D. O'Neill, G. Ramsay, B. P. Gompertz, R. Starling, M. Kennedy, 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 EP-WXT detected EP250109a (Li et al., GCN 38864); also observed by the Swift-XRT (Kennea et al., GCN 38867). Targeted observations were performed using the GOTO-South at 11:42:03 UT on 2025-01-09 (5.401 hours post-trigger). The stacked image is composed of 3x90s exposures 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 of the same pointings.
No new optical source within the EP-FXT localisation region (Li et al., GCN 38864) is identified to a 3-sigma limiting magnitude of L > 17.8. The shallower upper limit is attributed to the unfavourable weather conditions at the Siding Spring Observatory (SSO).
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).
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