TITLE: GCN CIRCULAR NUMBER: 39511 SUBJECT: EP250226a/GRB 250226A: 1.6m Mephisto observations DATE: 25/02/27 08:51:56 GMT FROM: Brajesh Kumar at SWIFAR, YNU <brajesh@ynu.edu.cn> Xingzhu Zou, Brajesh Kumar, Wenqiang Fan, Tao Wang, Jiayu Qi, Yuan Fang, Guowang Du, Jinghua Zhang, Helong Guo, Edoardo P. Lagioia, Yuanpei Yang, Xiangkun Liu, Xiaowei Liu (all SWIFAR, YNU) report on behalf of the Mephisto Team: The field of EP250226a/GRB 250226A (Jiang et al., GCN 39482; The Fermi team, GCN 39479) was observed with the 1.6m Multi-channel Photometric Survey Telescope (Mephisto) of Yunnan University located at Lijiang Observatory. Three exposures of 300s each in the MEPHISTO u, v, g, and r bands were simultaneously (ug, vr) obtained starting from 2025-02-26T17:59:42 (~ 11.5h after the trigger). In our stacked g and r band images, we detect a source at the position of the optical candidate (An et. al., GCN 39486; Zhu et. al., GCN 39487; Magnani et al., GCN 39488; Li et. al., GCN 39489; Aryan et al., GCN 39509) but not in u, v bands. The preliminary magnitudes and the 3-sigma upper limits are below: Start_Time(UT) | Band | Exp(s) | Mag/LimMag(AB) --------------------|------|--------|--------------- 2025-02-26T17:59:42 | u | 300*3 | > 22.6 2025-02-26T18:17:11 | v | 300*3 | > 23.0 2025-02-26T17:59:42 | g | 300*3 | 22.2 +/- 0.2 2025-02-26T18:17:11 | r | 300*3 | 21.2 +/- 0.1 ------------------------------------------------------------------------------------------------- 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 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. ------------------------------------------------------------------------------------------------- View this GCN Circular online at https://gcn.nasa.gov/circulars/39511. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...