TITLE: GCN CIRCULAR NUMBER: 39381 SUBJECT: GRB 250219A: 1.6m Mephisto optical upper limits DATE: 25/02/20 05:23:35 GMT FROM: Brajesh Kumar at SWIFAR, YNU <brajesh@ynu.edu.cn> Edoardo P. Lagioia, Yu Pan, Xiangkun Liu, Yaosong Yu, Guowang Du, Brajesh Kumar, Yuan Fang, Jinghua Zhang, Xinlei Chen, Xingzhu Zou, Yuanpei Yang (all SWIFAR, YNU), Xuhui Han, Pinpin Zhang, Liping Xin, Chao Wu, Jianyan Wei (all NAOC), Xiaowei Liu (SWIFAR, YNU) report on behalf of the Mephisto Team: The field of GRB 250219A detected by SVOM/ECLAIRs (Daigne et al., GCN 39376) and followed-up by Swift-XRT (Kennea et al. GCN 39379) was observed with the 1.6m Multi-channel Photometric Survey Telescope (Mephisto) of Yunnan University located at Lijiang Observatory. Simultaneous uvgr band photometric observations were conducted starting from 17:08:52 2025-02-19 UT (~1.26 hr after the trigger) and 4 frames with 120s exposure times were taken. There is no detection of the optical candidate (Xin et al. GCN 39380) in the stacked images of uvgr bands. The preliminary photometry and 3 sigma upper limits are listed below. Start_Time(UT) | Band | Exp(s) | LimMag (AB) ---------------------------|--------|------------ 2025-02-19T17:18:46 | u | 120*4 | >22.4 2025-02-19T17:08:52 | v | 120*4 | >22.2 2025-02-19T17:18:46 | g | 120*4 | >22.8 2025-02-19T17:08:52 | r | 120*4 | >22.8 ------------------------------------------------------------------------------------------------- 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/39381. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...