TITLE: GCN CIRCULAR NUMBER: 37966 SUBJECT: GRB 241030A: Multiband optical detection with Mephisto DATE: 24/10/30 13:14:05 GMT FROM: Brajesh Kumar at SWIFAR, YNU Weikang Lin (SWIFAR, YNU), Brajesh Kumar (SWIFAR, YNU), Guowang Du (SWIFAR, YNU), Yangwei Zhang (SWIFAR, YNU), Tao Wang (SWIFAR, YNU), Runnan Jiang (SWIFAR, YNU), Yaosong Yu (SWIFAR, YNU), Yu Pan (SWIFAR, YNU), Xingzhu Zou (SWIFAR, YNU), Xinlei Chen (SWIFAR, YNU), Jinghua Zhang (SWIFAR, YNU), Yuanpei Yang (SWIFAR, YNU), Yuan Fang (SWIFAR, YNU), Yehao Cheng (SWIFAR, YNU), Chenxu Liu (SWIFAR, YNU), Xuhui Han (NAOC), Pinpin Zhang (NAOC), Liping Xin (NAOC), Chao Wu (NAOC), Xiangkun Liu (SWIFAR, YNU), Xiaowei Liu (SWIFAR, YNU) report on behalf of the Mephisto Team: We performed uvgriz band observations of the optical afterglow of GRB 241030A (Fermi GBM team, GCN 37955 and Swift/BAT, Klingler et al., GCN 37956), using the 1.6m Multi-channel Photometric Survey Telescope (Mephisto) of Yunnan University located at Lijiang Observatory. The observations were started at 11:32:55 2024/10/30 UT (~5.7 h after the trigger). Multiple frames with exposure time 180s, 79s and 50s were taken in uv, gr, iz bands, respectively. The OT (Dichiara et al. GCN 37956, Watson et al., GCN 37957; Fernández-Rodríguez et al., GCN 37958; Zheng et al., GCN 37959; An et al., GCN 37960; Higuchi et al., GCN 37963; Qiu et al. GCN 37965) is clearly visible in the individual frames in all bands. The preliminary magnitudes are reported below which indicate the decay nature of the transient. The observations are continued. Exp-start (UT) Band Exp(s) Mag (AB) 2024/10/30 11:32:55 i 79 17.78 +/- 0.07 2024/10/30 11:32:55 g 50 18.71 +/- 0.10 2024/10/30 11:32:55 u 180 19.51 +/- 0.15 2024/10/30 11:37:54 z 79 17.72 +/- 0.14 2024/10/30 11:37:54 v 180 18.87 +/- 0.10 2024/10/30 11:37:54 r 50 18.13 +/- 0.05 -------------------------------------------------------------------------- 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. 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. --------------------------------------------------------------------------