TITLE: GCN CIRCULAR NUMBER: 43261 SUBJECT: EP-WXT trigger 01709250662 Mephisto and 50cm telescope follow-up DATE: 25/12/30 04:51:48 GMT FROM: elagioia@ynu.edu.cn Yuan Fang, Edoardo P. Lagioia, Jialei Zheng, Xian Liu, Jinghua Zhang, Chunsheng Xiao, Brajesh Kumar, Guowang Du, Xingzhu Zou, Xinlei Chen, Xufeng Zhu, Tao Wang, Yehao Cheng, Xinzhong Er, Yuanpei Yang, Xiangkun Liu, Xiaowei Liu (SWIFAR, YNU) report on behalf of the Mephisto Team The EP-WXT trigger 01709250662 (trigger time 2025-12-27T16:37:01), identified as a stellar flare associated to the High Proper Motion star PM J11474+6644 (Wang. C. et al., GCN 43241; Y.-H. I. Yin et al., GCN 43247) has been observed with the following facilities of the Yunnan University, located at the Lijiang Observatory: the 1.6m Multi-channel Photometric Survey Telescope (Mephisto) and one of the twin 50cm RC telescopes. A set of simultaneous multi-band (vrz and ugi) frames have been collected with Mephisto from 2025-12-27 UTC18:18:51 (~ 1.75 hr after the trigger) and continued until 2025-12-27 UTC 18:22:58. Preliminary analysis of the scientific frames indicate the following observed magnitudes: ----------------------------------------------- Start_Time(UT) | Band | Exp(s) | Mag (AB) --------------------|-------|--------|--------- 2025-12-27T18:18:51 | v | 45 | 16.88 2025-12-27T18:18:54 | r | 45 | 13.78 2025-12-27T18:18:53 | z | 45 | 11.10 2025-12-27T18:22:55 | u | 45 | 17.66 2025-12-27T18:22:58 | g | 45 | 14.65 2025-12-27T18:22:57 | i | 45 | 11.60 ----------------------------------------------- Ten frames in g-band have also been collected with the 50cm telescope starting from 2025-12-27 UTC 16:46:08 (~ 9 minutes after the trigger) and continued till 2025-12-27 UTC 16:54:40, for total duration of ~ 8.5 minutes. The first epoch observation shows a g-band luminosity of 14.02 mag, while the last epoch indicates 14.24 mag. Time series observations allowed to build a light curve in g-band which shows an average decay rate of ~ 0.024 mag/min. It is worth noticing that the g-band (AB) magnitude of PM J11474+6644 listed in the SIMBAD database is equal to 15.505 Mephisto (Multi-channel Photometric Survey Telescope) is a 1.6m 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/43261. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...