GCN Circular 42089
Subject
EP250821a: iTelescope T-59 possible detection of the optical counterpart
Event
Date
2025-10-03T12:59:37Z (5 days ago)
From
Takanori Sakamoto at AGU <tsakamoto@phys.aoyama.ac.jp>
Via
Web form
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.