GCN Circular 38277
Subject
GRB 241112B: Mephisto further optical observations
Date
2024-11-19T09:08:20Z (a month ago)
From
Brajesh Kumar at SWIFAR, YNU <brajesh@ynu.edu.cn>
Via
Web form
Xingzhu Zou, Brajesh Kumar, Yehao Cheng, Yuanpei Yang, Guowang Du, Weikang Lin, Yaosong Yu, Xinlei Chen, Yu Pan, Jinghua Zhang, Yuan Fang (all SWIFAR, YNU), Xuhui Han, Pinpin Zhang, Liping Xin, Chao Wu (all NAOC), Xiangkun Liu, Xiaowei Liu (all SWIFAR, YNU) report on behalf of the Mephisto Team:
We re-observed the field of GRB 241112B (sb24111201) detected by SVOM/ECLAIRs and SVOM/GRM (Yang et al., GCN 38173; Liu et al., GCN 38180) with the 1.6m Multi-channel Photometric Survey Telescope (Mephisto) of Yunnan University located at Lijiang Observatory. Multiple frames of 300 s were obtained in uvgriz bands between 16:41:28 - 17:15:14 UT on 2024-11-12 (~5.7 hr after the trigger), although affected with high background due to moon light. The optical afterglow candidate (Qui et al., GCN 38179; Turpin et. al, GCN 38181; Osborne et. al, GCN 38182; Du et. al, GCN 38183) is faintly detected in our stacked r and i band images but not in other bands. The estimated PSF photometric magnitudes and the 3-sigma upper limits are below. Based on the Mephisto observations and estimated magnitudes (Du et. al, GCN 38183), we obtained the temporal decay indexes as alpha = 0.93 and 1.02 for r band and i band, respectively, where alpha is defined as Flux=(t-T0)^-alpha. The T0 is SVOM/ECLAIRs triggered time (Yang et al., GCN 38173).
Obs-start time band Exp(s) Mag (AB)
16:41:28T2024-11-12 u 300*3 >21.78
17:04:47T2024-11-12 v 300*3 >21.75
16:41:28T2024-11-12 g 300*3 >22.03
17:04:47T2024-11-12 r 300*3 21.00 +/- 0.14
16:41:28T2024-11-12 i 294*3 20.68 +/- 0.22
17:04:47T2024-11-12 z 294*3 >20.23
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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.
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