TITLE:   GCN CIRCULAR
NUMBER:  36335
SUBJECT: EP240426b: AST3-2 optical upper limit 
DATE:    24/04/27 16:54:44 GMT
FROM:    Tianrui Sun at Purple Mountain Obs,CAS <trsun@pmo.ac.cn>

Tian-Rui Sun, Yan-Long Hua, Jin-Jun Geng, Xue-Feng Wu, Ke-Lai Meng (Purple Mountain Observatory, CAS), Xiao-Yan Li, Zheng-Yang Li, Yun Li, Xiang-Yan Yuan (Nanjing Institute of Astronomical Optics & Technology, CAS), Lifan Wang (TAMU), Xiao-Feng Wang, Mao-Kai Hu (Tsinghua University), Lei Hu (CMU) report on behalf the AST3 Team:

Following the detection of EP240426b by Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) (Pan et al. GCN 36330),
we use Antarctic Survey Telescope 3-2 at Dome A, Antarctic (Latitude -80.4173, Longitude 77.0950) for follow-up.
Our observation started on 2024-04-27T12:44:01. 
No obvious optical source was detected with an uncertainty of 3 arcmin in radius.
Our detection limit on the coadded images is down to 19.2 mag for total 36x60s with filter i.
We use the ATLASREFCAT2 (Tonry et al. 2018) as the magnitude calibration reference.

We thank Prof. Michael Ashley (UNSW) for his excellent support on the operation of AST3-2.