TITLE: GCN CIRCULAR NUMBER: 40031 SUBJECT: GRB 250403A: 1.6m Mephisto multi-band optical detection DATE: 25/04/03 17:46:43 GMT FROM: Chenxu Liu at Mephisto Team cxliu@ynu.edu.cn
Guowang Du (SWIFAR, YNU), Ziwei Li (SWIFAR, YNU), Dezi Liu (SWIFAR, YNU), Yaosong Yu (SWIFAR, YNU), Chenxi Shang (SWIFAR, YNU), Chenxu Liu (SWIFAR, YNU), Jinghua Zhang (SWIFAR, YNU), Yuan Fang (SWIFAR, YNU), Xufeng Zhu (SWIFAR, YNU), Tao Wang (SWIFAR, YNU), Xinlei Chen (SWIFAR, YNU), Xingzhu Zou (SWIFAR, YNU), Xuhui Han (NAOC), Pinpin Zhang (NAOC), Liping Xin (NAOC), Chao Wu (NAOC), Yu Pan (SWIFAR, YNU), Brajesh Kumar (SWIFAR, YNU), Yuanpei Yang (SWIFAR, YNU), Xiangkun Liu (SWIFAR, YNU), Xiaowei Liu (SWIFAR, YNU) report on behalf of the Mephisto Team:
We performed simultaneous multi-band photometric observations of GRB 250403A (SVOM burst-id sb25040305) detected by SVOM/ECLAIRs (Y. Julakanti et. al. 2025, GCN 40026) and by Fermi (Fermi GBM team, GCN 40025) with the 1.6m Multi-channel Photometric Survey Telescope (Mephisto) of Yunnan University located at Lijiang Observatory. The observations were initiated at 15:17:48UTC 2025-04-03 (i.e., 148s after the Swift/BAT trigger) and are still ongoing at the time of this report. Multiple frames were obtained in uvgriz- bands. The optical counterpart is clearly detected in all bands. The photometry of the initial frames is listed below:
UT start |Band | Exp | Mag (AB) ---------------------------|-------|---------------- 2025/04/03T15:25:37 | u |180s |17.92 +/- 0.12 2025/04/03T15:17:48 | v |180s |16.51 +/- 0.03 2025/04/03T15:25:38 | g | 50s |17.16 +/- 0.05 2025/04/03T15:17:49 | r | 50s |15.64 +/- 0.01 2025/04/03T15:25:38 | i | 79s |16.68 +/- 0.04 2025/04/03T15:17:49 | z | 79s |15.27 +/- 0.02
Our results are consistent with the previously reported circulars (R. Starling et al., GCN 40028; Wu et al., GCN 40029). Further analysis of the additional images is ongoing. ---------------------------------------------------------- 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. ----------------------------------------------------------
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