TITLE: GCN CIRCULAR NUMBER: 39447 SUBJECT: EP250223a: 1.6m Mephisto and 50cm array observations DATE: 25/02/24 10:02:52 GMT FROM: Brajesh Kumar at SWIFAR, YNU brajesh@ynu.edu.cn
Helong Guo, Guowang Du, Yu Pan, Xinlei Chen, Brajesh Kumar, Xiaotong Chen, Yiheng Xie, Yuan Fang, Xingzhu Zou, Yuanpei Yang, Jinghua Zhang, Dezi Liu, Xiangkun Liu, Xiaowei Liu (all SWIFAR, YNU) report on behalf of the Mephisto Team:
The field of EP250223a detected by EP Team (Lian et al., GCN 39429) was observed with the 1.6m Multi-channel Photometric Survey Telescope (Mephisto) and 50cm array facilities of Yunnan University located at Lijiang Observatory. Simultaneous uvgr band images with different exposure times were acquired with Mephisto starting from 15:20:12 2025-02-23 UT (~15.6 minutes after the trigger) and with 50cm array in iz bands starting from 15:49:08 2025-02-23 UT (~44.5 minutes after the trigger). The afterglow candidate (Lipunov et al., GCN 39434; Hauptmann et al., GCN 39436; Kennea et al., GCN 39437; Levan et al., GCN 39438; Wu et al., GCN 39439; Pérez-Fournon et al., GCN 39440; Izzo et al., GCN 39441; Xin et al., GCN 39445) is clearly detected in each v, g, r band and in the stacked u band images taken with Mephisto. The candidate is also visible in the stacked i band image of 50 cm array but not in the stacked z band. The preliminary magnitudes and 3-sigma upper limit are below:
1.6m Mephisto Start_Time(UT) | Band | Exp(s) | Mag/LimMag(AB) --------------------|------|--------|---------------- 2025-02-23T16:00:53 | u | 300*3 | 20.97 +/- 0.29 2025-02-23T15:25:14 | v | 180 | 19.93 +/- 0.22 2025-02-23T15:20:12 | g | 10 | 18.11 +/- 0.12 2025-02-23T15:25:14 | r | 50 | 18.17 +/- 0.07
50CM array Start_Time(UT) | Band | Exp(s) | Mag/LimMag(AB) --------------------|------|--------|--------------- 2025-02-23T15:49:08 | i | 300*3 | 18.89 +/- 0.11 2025-02-23T15:49:08 | z | 300*3 | >18.81
------------------------------------------------------------------------------------------------- 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.
The 50cm array consists of two 50cm telescopes for wide-field surveys and also serves as the supporting facility for monitoring the Mephisto detected targets. -------------------------------------------------------------------------------------------------
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