TITLE:   GCN CIRCULAR
NUMBER:  42089
SUBJECT: EP250821a: iTelescope T-59 possible detection of the optical counterpart
DATE:    25/10/03 12:59:37 GMT
FROM:    Takanori Sakamoto at AGU <tsakamoto@phys.aoyama.ac.jp>

H. Ban, T. Katou, Y. Nagata, K. Hotta, Y. Kawakubo, M. Serino, T. Sakamoto (AGU)

We observed the field of EP250821a detected by the Einstein Probe (EP) 
(Hu et al., GCN Circ. 41459) with the iTelescope.Net
(http://www.itelescope.net) T59 (Planewave 20" CDK) telescope located at 
the Siding Spring Observatory, Australia. We took nine images of 120-second 
exposures in the Red filter starting from August 21 at 10:25:34 (UT), 
about 3 hours after the trigger, and stopped at 12:48:14 (UT). Please note 
that there were no observations between 10:33 and 11:30, and 
between 11:39 and 12:41 due to our scheduling error.

We have a weak detection of the optical counterpart 
(Dichiara et al., GCN Circ. 41469; Li et al., GCN Circ. 41470; 
Yao et al., GCN Circ. 41485) in the stacked image of the first 
three exposures from 10:25:34 to 10:32:47 UT. The estimated magnitude 
is ~18.5. No optical counterpart was detected in the following six images 
collected between 11:30:00 and 12:48:14 (UT). The 5-sigma upper limit 
of the stacked image of the last six images is 17.5 mag.