TITLE: GCN CIRCULAR NUMBER: 40442 SUBJECT: EP250511a: Mephisto optical upper limits DATE: 25/05/12 14:58:06 GMT FROM: Brajesh Kumar at SWIFAR, YNU <brajesh@ynu.edu.cn> Shiyan Zhong, Jianhui Lian, Xufeng Zhu, Yicheng Jin, Dan Zhu, Guowang Du, Xingzhu Zou, Brajesh Kumar, Yuan Fang, Helong Guo, Yu Pan, Xinlei Chen, Jianghua Zhang, Edoardo P. Lagioia, Yuanpei Yang, Xiangkun Liu, Xiaowei Liu (all SWIFAR, YNU) report on behalf of the Mephisto Team: The field of EP250511a (Lian et al., GCN 40429) was observed with the 1.6-meter Multi-channel Photometric Survey Telescope (Mephisto) of Yunnan University, located at Lijiang Observatory. The simultaneous observations in Mephisto u/g/i bands were started from 2025-05-11T13:58:03 (~6 h after the trigger). The field was also simultaneously observed in v/r/z bands, starting from 2025-05-11T14:07:46. In our stacked u/g/i images and the single frame v/z images (r-band image was saturated due to high background of moon light), we did not detect any source at the position reported by Schneider et. al. (GCN 40431) and Li et al. (GCN 40433). The preliminary 3-sigma upper limits (listed below) are consistent with Perez-Garcia et al. (GCN 40430), Lipunov et al. (GCN 40432), and Brivio et al. (GCN 40435). Start_Time (UT) | Band | Exp(s) | LimMag(AB) --------------------|------|--------|------------- 2025-05-11T13:58:03 | u | 180*2 | > 19.965 2025-05-11T14:07:46 | v | 180*1 | > 19.152 2025-03-09T20:07:03 | g | 60+180 | > 19.876 2025-05-11T13:58:02 | i | 180*2 | > 19.810 2025-05-11T14:07:45 | z | 180*1 | > 18.032 ------------------------------------------------------------------------------------------------- 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/40442. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...