TITLE:   GCN CIRCULAR
NUMBER:  39854
SUBJECT: EP250321a: TNOT Observation of Optical Counterpart
DATE:    25/03/23 16:31:37 GMT
FROM:    Xiaofeng Wang at Tsinghua University <wang_xf@mail.tsinghua.edu.cn>

Haichang Zhu (THU), A. Iskandar(XAO), Xiaofeng Wang (THU), and Letian Wang (XAO) report the  detection of the optical counterpart that is associated with the X-ray transient EP250321a (Hu et al., GCN 39800; 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). 

We obtained the r-band images (~12.44 hours after the burst) with the 80~cm Tsinghua-Nanshan Optical Telescope (TNOT) located at Nanshan Station of Xinjiang Astronomy observatory, starting on 2025-03-21 (UT)18:36:10. From the stacked images with a total exposure time of 100sx15, we did not detect the optical afterglow down to a limiting magnitude of about 22.2 mag (MJD=60755.775). 

The above photometric result is calibrated using the field stars from the Pan-STARRS catalog and is not corrected for the Galactic extinction.