TITLE: GCN CIRCULAR NUMBER: 43807 SUBJECT: EP260221a: Liverpool Telescope detection of COLIBRÍ counterpart candidate DATE: 26/02/22 19:53:08 GMT FROM: Rob Eyles-Ferris at U of Leicester <raje1@leicester.ac.uk> R. A. J. Eyles-Ferris and P. T. O’Brien (Leicester) report on behalf of a larger collaboration: We observed the field of EP260221a (Zhang et al., GCN 43791; Liu et al., GCN 43802) with the 2m Liverpool Telescope on La Palma using the IO:O instrument. We obtained 6x200s exposures in the SDSS i’ and 8x200s exposures in the SDSS z’ filters starting at 2026-02-22 00:47:58 UT, approximately 14.1 hours after the X-ray detection. Within the EP/FXT localisation (Liu et al., GCN 43802), we detect no new sources in our stacked images consistent with the results of Mandarakas et al. (GCN 43793), Kumar et al. (GCN 43794), He et al. (GCN 43798), Lipunov et al. (GCN 43803), and Levan et al. (GCN 43805). At the position of the candidate counterpart identified by Watson et al. (GCN 43806), we measure i’ = 22.21 +/- 0.12 and z’ = 22.29 +/- 0.18 with photometry calibrated to Pan-STARRS and not corrected for Galactic extinction. As pointed out by Watson et al. (GCN 43806), this is significantly brighter than the magnitudes catalogued in Legacy DR10 and suggests this could indeed be the counterpart of EP260221a. We derive 3-sigma upper limits of i’ > 23.4 and z’ > 23.0 for our stacked images. View this GCN Circular online at https://gcn.nasa.gov/circulars/43807. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...