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GCN Circular 36098

EP240413A: GOTO optical upper limits
2024-04-14T20:04:34Z (a month ago)
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K. Ackley; B. P. Gompertz; P. O'Brien; G. Ramsay; A. Levan; R. Starling; M. J. Dyer; J. Lyman; K. Ulaczyk; F. Jimenez-Ibarra; A. Kumar; D. O'Neill; D. Steeghs; D. K. Galloway; V. Dhillon; 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) performed a targeted observation in response to the EP-WXT trigger EP240413A (Lian et al., GCN 36086) at 11:42:34 UT on 2024-04-14, starting approximately 21 hours after the EP-WXT trigger and 7 hours after EP-FXT follow-up observations (Li et al., GCN 36092). The observation consisted of a 6x60s exposure in the GOTO L-band (400-700 nm).

Images were processed immediately after acquisition using the GOTO pipeline. No optical counterpart to the X-ray counterpart candidate detected by EP-FXT (Li et al., GCN 36092) is seen to a 3-sigma limit of L > 20.4 magnitudes (AB). The last visit to this field occurred at 14:27:11 on 2024-04-13, approximately 12 minutes before the EP-WXT trigger, providing a pre-detection 3-sigma limit of L > 21.1 magnitudes (AB).

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

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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