TITLE: GCN CIRCULAR NUMBER: 43134 SUBJECT: GRB 251214B: 1.6m Mephisto observations with newly installed mosaic cameras DATE: 25/12/16 04:17:28 GMT FROM: Brajesh Kumar at SWIFAR, YNU <brajesh@ynu.edu.cn> Weikang Lin, Guowang Du, Ziwei Li, Brajesh Kumar, Jiayu Qi, Donglin Gao, Yu Pan, Yuan Fang, Xinlei Chen, Xingzhu Zou, Xufeng Zhu, Tao Wang, Jinghua Zhang, Xinzhong Er, Yuanpei Yang, Xiangkun Liu, Xiaowei Liu (SWIFAR, YNU) report on behalf of the Mephisto Team: We performed simultaneous multi-band photometric observations of GRB 251214B (Fermi GBM Team, GCN Circ. 43088; Eyles-Ferris et al., GCN Circ. 43089) with the newly installed three mosaic cameras on the 1.6m Multi-channel Photometric Survey Telescope (Mephisto) of Yunnan University located at the Lijiang Observatory. The observations were initiated at 11:31:54UTC2025-12-14 (~2.5 hours after the Swift/BAT trigger). Multiple frames were obtained in uvgriz - bands. The optical counterpart is detected in the stacked images of g, r bands and single frames of i, z bands, but there is no detection in the u and v band stacked images. The preliminary photometric magnitudes and 3-sigma upper limits are listed below. These magnitudes are not corrected for the Galactic extinction in the direction of the burst. UT Start |Band | Exposure(s)| mag/LimMag (AB) ---------------------|-----|------------|---------------- 2025-12-14T11:49:07 | u | 300.0*2 | >22.68 2025-12-14T11:31:54 | v | 300.0*2 | >22.47 2025-12-14T11:49:09 | g | 300.0*2 | 21.08 (+/-0.12) 2025-12-14T11:31:56 | r | 300.0*2 | 20.64 (+/-0.08) 2025-12-14T11:49:09 | i | 300.0 | 19.50 (+/-0.07) 2025-12-14T11:31:56 | z | 300.0 | 18.60 (+/-0.14) The optical detection of the burst is consistent with Eyles-Ferris et al. 2025 (GCN 43089); Kang et al. 2025 (GCN 43093); Gress et al. 2025 (GCN 43095); Fu et al. 2025 (GCN 43097); Gupta et al. 2025 (GCN 43100); Watson et al. (GCN 43103); Kuin et al. (GCN 43105); Pérez-Fournon (GCN 43123); Volnova et al. (GCN 43124); Postigo et al. (GCN 43131). ------------------------------------------------------------------------------------------------- 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 Mephisto mosaic cameras were installed in October 2025. The first light was achieved in all three channels on 10 October 2025, and these are currently in the commissioning phase. 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/43134. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...