TITLE:   GCN CIRCULAR
NUMBER:  46009
SUBJECT: EP261015a: GSP multiband optical follow-up observations
DATE:    26/10/22 15:15:22 GMT
FROM:    fufu Glow <fufuglow70@gmail.com>

J. F. Gou, W. X. Li, S. J. Xue (NAOC); M. Andrews, D. A. Howell, C. McCully, J. Ridenbaugh and K. Wynn (Las Cumbres Observatory) report:
We observed the field of the Einstein Probe fast X-ray transient EP261015a (Li et al., GCNs 45956 and 45969) using MuSCAT3 on the Las Cumbres Observatory (LCO) 2-m Faulkes Telescope North at Haleakala, Hawaii. Observations were obtained simultaneously in g, r, i, and z_s from 2026 October 20, 14:06:51 to 14:29:01 UTC, with four 300-s exposures in each band, approximately 5.0 days after the EP/WXT event onset.
Following subtraction of same-band archival Legacy Survey DR10 templates with HOTPANTS, we detect residual emission at the position of the optical counterpart reported by Corcoran et al., GCNs 45955 and 45972; Fortin et al., GCN 45991; Pawar et al., GCNs 45998 and 46006; Shivaprasad et al., GCN 46000; Pankov et al., GCN 46003. Preliminary PSF photometry using AutoPhOT (Brennan & Fraser 2022), calibrated against nearby Pan-STARRS DR2 stars, gives:

                Magnitude (AB)
     g            23.51 ± 0.22
     r            22.26 ± 0.06
     i          > 22.34 (5 sigma)
     z          > 22.14 (5 sigma)

These observations were taken as part of the Global Supernova Project (GSP).