TITLE: GCN CIRCULAR NUMBER: 38774 SUBJECT: GRB 250101A: 1.6m Mephisto multi-band optical followup DATE: 25/01/02 05:41:08 GMT FROM: Brajesh Kumar at SWIFAR, YNU <brajesh@ynu.edu.cn> Jinghua Zhang, Guowang Du, Yangwei Zhang, Xufeng Zhu, Fanchuan Kong, Chenxi Shang,Yuan Fang, Xinlei Chen, Xingzhu Zou, Yu Pan, Brajesh Kumar, Yuanpei, Yang, Xiangkun Liu, Xiaowei Liu (all SWIFAR, YNU) report on behalf of the Mephisto Team: We performed simultaneous multi-band photometric observations of GRB 250101A detected by Swift/BAT (Page et. al., GCN 38752) with the 1.6m Multi-channel Photometric Survey Telescope (Mephisto) of Yunnan University located at Lijiang Observatory. The observations were initiated at 13:26:07 UTC 2025-01-01 (i.e., 197 s after the Swift/BAT trigger) and continuously followed-up for several hours. Multiple frames were obtained in uvgriz bands. The optical counterpart is clearly detected in all bands. The photometry of the initial frames is the following: UT start band Exp Mag(AB) 2025/01/01T13:26:07 u 180s 18.66 +/- 0.04 2025/01/01T13:26:08 g 50s 17.07 +/- 0.01 2025/01/01T13:26:08 i 79s 16.30 +/- 0.01 2025/01/01T13:30:02 v 180s 18.59 +/- 0.03 2025/01/01T13:30:04 r 50s 17.30 +/- 0.02 2025/01/01T13:30:04 z 79s 16.73 +/- 0.05 Our results are consistent with the previously reported circulars (Li et al., GCN 38753; Mohan et al., GCN 38754; Zhu et al., GCN 38755; Budnev et al., GCN 38756; Wu et al., GCN 38758; Moskvitin et al., GCN 38762; Odeh et al., GCN 38763, Hu et al., GCN 38764; D'Avino et al., GCN 38768; Escudero-Coca et al., GCN 38769). Further analysis of the additional images is ongoing. -------------------------------------------------------------------------- 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. -------------------------------------------------------------------------- View this GCN Circular online at https://gcn.nasa.gov/circulars/38774. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...