TITLE: GCN CIRCULAR NUMBER: 39832 SUBJECT: EP250321a: KAIT optical observations DATE: 25/03/22 05:56:29 GMT FROM: Weikang Zheng at UC Berkeley weikang@berkeley.edu

WeiKang Zheng (UCB), Xuhui Han (NAOC), Pinpin Zhang (NAOC) and

Alexei V. Filippenko (UCB) report on behalf of the KAIT GRB team:

The 0.76-m Katzman Automatic Imaging Telescope (KAIT), located at

Lick Observatory, automatically responded to EP250321a detected

by Einstein Probe (Hu et al., GCN 39800) starting at 07:05:35 UT,

about 0.93 hours after the trigger and lasted for ~4 hours. A set

of 60s exposure images were obtained in the clear (roughly R)

filters. We detect the optical afterglow (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) with a mag of 18.7 +/- 0.2 (Vega) at 0.93

hours, it decayed to ~20.7 +/- 0.3 mag at ~5.4ks. The OT started

getting brighter slowly and reach a peak of ~19.5 +/- 0.2 mag

around 9.5ks, then decayed after that.

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