TITLE: GCN CIRCULAR NUMBER: 43891 SUBJECT: EP260227a: Mephisto optical detection DATE: 26/03/01 14:58:50 GMT FROM: Brajesh Kumar at SWIFAR, YNU <brajesh@ynu.edu.cn> Shiyan Zhong, Hongguang Li, Qinhao Shao, Yuan Fang, Jian Cui, Guowang Du, Yu Pan, Xingzhu Zou, Xinlei Chen, Brajesh Kumar, Jianghua Zhang, Edoardo P. Lagioia, Yuanpei Yang, Xiangkun Liu, Xiaowei Liu (SWIFAR, YNU) report on behalf of the Mephisto Team: The field of EP260227a (Wang et al., GCN 43869) was observed with the 1.6-meter Multi-channel Photometric Survey Telescope (Mephisto) of Yunnan University located at Lijiang Observatory. The simultaneous observations in Mephisto u/g/i bands were started from 2026-02-27T20:20:38 (~8 minutes after the trigger). The field was again simultaneously observed in v/r/z bands (starting from 2026-02-27T20:23:47). We detected a source at the position reported by Eyles-Ferris et. al. (GCN 43867) and other groups Li et al., (GCN 43868); Fu et al, (GCN 43873); Mandarakas et al., (GCN 43874); Eyles-Ferris and Tanvir et al., (GCN 43875); Malesani et al., (GCN 43876); Eyles-Ferris et al., (GCN 43877); Strausbaugh et al., (GCN 43879); Bochenek et al., (GCN 43880); Gassert et al., (GCN 43881); Gupta et al., (GCN 43884); Ma et al., (GCN 43887) and Eyles-Ferris et al., (GCN 43888). The preliminary photometry results (without extinction correction) are listed below: Start_Time (UT) | Band | Exp(s) | Mag/LimMag(AB) --------------------|------|--------|-------------------- 2026-02-27T20:20:38 | u | 45 | >20.86 (3-sigma) 2026-02-27T20:20:38 | g | 45 | 20.58 +/- 0.32 2026-02-27T20:20:38 | i | 45 | 19.92 +/- 0.18 --------------------|------|--------|-------------------- 2026-02-27T20:23:47 | v | 45 | >20.80 (3-sigma) 2026-02-27T20:23:47 | r | 45 | 20.13 +/- 0.25 2026-02-27T20:23:47 | z | 45 | >20.28 (3-sigma) ------------------------------------------------------------------------------------------------- Mephisto (Multi-channel Photometric Survey Telescope) is a 1.6-m 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 Mephisto mosaic cameras were installed in October 2025. The first light was achieved in all three channels on 10 October 2025, and these are currently in the commissioning phase. Here, we note that the current data processing pipeline is still at a preliminary stage, with flux calibration precision in each band at the level of about 5% or even higher. ------------------------------------------------------------------------------------------------- View this GCN Circular online at https://gcn.nasa.gov/circulars/43891. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...