TITLE:   GCN CIRCULAR
NUMBER:  39837
SUBJECT:  EP250321a: Liverpool Telescope optical follow-up
DATE:    25/03/22 18:25:33 GMT
FROM:    A. Bochenek at Liverpool John Moores University <a.m.bochenek@2023.ljmu.ac.uk>

A. Bochenek and D. A. Perley (LJMU) report:
 
We observed the field of the fast X-ray transient EP250321a (Hu et al., GCN 39800) using the IO:O optical camera on the 2m robotic Liverpool Telescope. We obtained 6x100s exposures in the SDSS r’ and i’ filters, starting at 2025-03-22 00:24:35 UT, approximately 18.24 hours after the trigger.
 
We report a detection in the stacked images in the i band at the position of the optical counterpart (Fu et al., GCN 39804) of the magnitude i = 22.08 ± 0.16. In the r-band stacked images, we report a non-detection with the 3-sigma limiting magnitude of r > 22.19 mag. Our results are in agreement with previous observations (Fu et al., GCN 39804; Perez-Garcia et al al., GCN 39805; Brivio et al., GCN 39807; Zhu et al., GCN 39809; Becerra et al., GCN 39810; Pérez-Fournon et al., GCN 39812; Lee et al., GCN 39815; Ghosh et al., GCN 39816; Han et al., GCN 39817; Jin et al., GCN 39822; Zhu et al., GCN 39827; Gill et al., GCN 39831; Zheng et al., GCN 39832; Pankov et al., GCN 39836).

MJD (mid)          T_mid - T_0      Filter     Mag. (AB)
60756.02120        18.34 h             r         > 22.19
60756.02976        18.55 h             i         22.08 ± 0.16
 
The photometry was calibrated using nearby PanSTARRS secondary standards and was not corrected for extinction.