TITLE: GCN CIRCULAR NUMBER: 38404 SUBJECT: EP241126a: 1.6m Mephisto Optical Upper Limits DATE: 24/12/01 15:38:10 GMT FROM: Brajesh Kumar at SWIFAR, YNU brajesh@ynu.edu.cn

Xingzhu Zou, Helong Guo, Xinlei Chen, Yu Pan, Yaosong Yu, Guowang Du, Xufeng Zhu, Tao Wang, Brajesh Kumar, Yuan Fang, Jinghua Zhang, Yuanpei Yang, Xiangkun Liu, Xiaowei Liu (SWIFAR, YNU) report on behalf of the Mephisto Team:

The field of fast X-ray transient EP241126a (Hu et al., GCN 38335; Zheng et al., GCN 38339) was observed with the 1.6m Multi-channel Photometric Survey Telescope (Mephisto) of Yunnan University located at Lijiang Observatory. The observations were carried out in the v and r bands, ~15.8 hours after the EP trigger. We do not detect the optical counterpart (Fu et al., GCN 38337; Li et al., GCN 38338; Geng et al., GCN 38357; Qiu et al., GCN 38378; Malesani et al., GCN 38385) in the stacked images (total exposure 420 sec in each band). The 3-sigma upper limits in v and r bands (mid-UT 2024-11-27T11:28:36) are 22.2 and 22.3 mag respectively, which is consistent with Lai et al. (GCN 38344).

----------------------------------------------------------------------- Mephisto (Multi-channel Photometric Survey Telescope) is a 1.6m wide-field multi-channel telescope, the first of its type in the world, capable of imaging the same field of view in three optical bands simultaneously. It provides real-time, high-quality colors of stellar objects. The on-site telescope assemblage and commissioning were carried out in September 2022. The first light in all three channels was achieved on 2023 December 21. -------------------------------------------------------------------------

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