TITLE: GCN CIRCULAR NUMBER: 37140 SUBJECT: GRB 240811A: Upper limits with Mephisto DATE: 24/08/11 18:40:19 GMT FROM: Brajesh Kumar at SWIFAR, YNU Guowang Du, Yuan Fang, Xufeng Zhu, Yehao Cheng, Yuze Zhao, Brajesh Kumar, Weikang Lin, Yuanpei Yang, Xinzhong Er, Xiangkun Liu and Xiaowei Liu (SWIFAR, YNU) report on behalf of Mephisto team: We performed simultaneous multi-band photometric observations of GRB 240811A (Page & Gupta, GCN 37136) using 1.6m Multi-channel Photometric Survey Telescope (Mephisto) of Yunnan University located at Lijiang Observatory. The observations were started ~37 min after the notice and multiple frames in uvgriz bands were acquired. The upper limits of our initial frames are the following: UTC(2024-08-11) Exptime(s) filter Mag(AB) 14:55 180 v >21.07 14:55 60 r >20.96 14:55 120 z >19.98 15:08 180 u >21.03 15:08 60 g >20.97 15:08 120 i >20.86 ---------------------------------------------------------------------------------- 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. ----------------------------------------------------------------------------------