TITLE:   GCN CIRCULAR
NUMBER:  39796
SUBJECT: EP250226a/GRB 250226A: KAIT optical observations
DATE:    25/03/21 06:54:07 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, observed the field of EP250226a/GRB 250226A

(Fermi GBM team, GCN 39479; Jiang et al., GCN 39482; Jiang et al.,

GCN 39513; Zhang et al., GCN 39492; Thakur et al., GCN 39518;

Pathak et al., GCN 39530; Svinkin et al., GCN 39542; Ronchini

et al., GCN 39672) on Feb 26 at 09:27:20 (~2.88 hours after GBM

trigger) and lasted for 4 hours. A set of 160x60s images were

obtained in the clear (roughly R) filters. We detect the optical

afterglow (An et. al, GCN 39486; Zhu et. al, GCN 39487; Magnani

et. al, GCN 39488; Li et. al, GCN 39489; Aryan et. al, GCN 39509;

Zou et al., GCN 39511; Li et. al, GCN 39514; Jiang et al., GCN 39515;

Poidevin et al., GCN 39524; Tanasan et al., GCN 39554) in our single

images. We measure the OT brightness to be 19.6 +/- 0.1 mag (Vega)

at 2.88 hours after GBM trigger. We observed the OT again on the

following night with 60x60s exposures and detected the OT in the

coadd image with 22.2 +/- 0.2 mag (Vega) at a mid time of 1.17 days.

This gives a decay index of -1.04 between the two nights.