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. View this GCN Circular online at https://gcn.nasa.gov/circulars/42089. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...