TITLE: GCN CIRCULAR NUMBER: 43321 SUBJECT: GRB 251230A/EP-WXT trigger 01709250693: Mephisto optical upper limits DATE: 26/01/04 15:26:20 GMT FROM: Dr. Kaushik Chatterjee at SWIFAR, Yunnan University <mails.kc.physics@gmail.com> Kaushik Chatterjee, Guowang Du, Yu Pan, Yifei Ding, Guangya Zeng, Brajesh Kumar, Yuan Fang, Jinghua Zhang, Xingzhu Zou, Xinlei Chen, Xufeng Zhu, Tao Wang, Xinzhong Er, Yuanpei Yang, Xiangkun Liu, Xiaowei Liu (SWIFAR, YNU) report on behalf of the Mephisto Team: The EP-WXT trigger 01709250693 (trigger time 2025-12-30T01:22:21), identified as EP251230a/GRB251230A (Lanava et al., GCN 43252; Li et al. GCN 43255; Wang. C. et al., GCN 43259; Osborne et al., GCN 43263) was observed with the following facility of the Yunnan University, located at the Lijiang Observatory: the 1.6m Multi-channel Photometric Survey Telescope (Mephisto). A set of simultaneous multi-band (ugi and vrz) frames were collected starting from 2025-12-30 UTC19:34:28 (~ 16.9 hr after the trigger) and continued till 2025-12-30 UTC20:00:18. The optical counterpart reported previously (Busmann et al., GCN 43258; Masi et al., GCN 43260; Ghosh et al., GCN 43262; Ma et al., GCN 43265) was not detected in our stacked frames and the upper limits (5 sigma) are listed below. --------------------------------------------------- Start_Time(UT) | Band | Exp(s) | LimMag (AB) --------------------------------------------------- 2025-12-30T19:34:28 | u | 45.0*7 | >21.08 2025-12-30T19:54:43 | v | 45.0*6 | >20.89 2025-12-30T19:34:30 | g | 45.0*6 | >21.36 2025-12-30T19:54:45 | r | 45.0*6 | >21.38 2025-12-30T19:34:30 | i | 45.0*7 | >21.04 2025-12-30T19:54:44 | z | 45.0*6 | >20.32 --------------------------------------------------- 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. The facility is operated by the South-Western Institute for Astronomy Research (SWIFAR), Yunnan University. 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 presently, these are under the commissioning phase. All the data have been reduced by the Mephisto data processing pipeline. 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/43321. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...