EP241126a: 1.6m Mephisto Optical Upper Limits

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. -------------------------------------------------------------------------