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GCN Circular 36257

LIGO/Virgo/KAGRA S240422ed: GOTO counterpart search
2024-04-23T16:55:56Z (3 months ago)
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K. Ackley, M. J. Dyer, J. Lyman, D. O'Neill, K. Ulaczyk; F. Jimenez-Ibarra, A. Kumar, B. Godson, T. Killestein, B. Gompertz, M. Kennedy, S. Belkin, J. Rana, D. Steeghs, D. Galloway, V. Dhillon, P. O'Brien, G. Ramsay, 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 optical observations with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022) in response to the LIGO/Virgo/KAGRA candidate NSBH event S240422ed (The LIGO-Virgo-KAGRA Collaboration, GCN 36236). Targeted observations covering 260 sqr. degrees or 96.2% of the localisation probability of the Bilby skymap (The LIGO-Virgo-KAGRA Collaboration, GCN 36240) were performed between 21:38 UT and 23:09 UT April 22 2024 (starting 2.7 minutes after trigger) with GOTO-N and 08:33 UT and 12:47 UT on April 23 2024 (starting 10.96 hours after trigger) with GOTO-S.

Exposures were taken in L-band (400-700 nm passband) and the median 5 sigma depth was L = 18.84 AB magnitudes with GOTO-N and 19.56 with GOTO-S, under bright moon and partly cloudy conditions. Magnitudes were calibrated using ATLAS-REFCAT2 (Tonry et al. 2018) and not corrected for Galactic extinction.

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 catalogs. Human vetting was carried out in real time on any candidates that passed the above checks. After filtering for image quality, the total vetted region covered 45% of the skymap probability. 

No significant counterpart sources that can be associated with S240422ed have been identified so far, consistent with reports from other search efforts.

Observations are ongoing and any notable candidates will be reported via TNS and GCN.

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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