GCN Circular 37242
Subject
GRB 240821A: GMG Optical Upper Limit
Date
2024-08-23T06:49:53Z (3 months ago)
From
Rui-Zhi Li at Yunnan Observatories, CAS <liruizhi@ynao.ac.cn>
Via
email
R.-Z. Li, B.-T. Wang, F.-F. Song, J. Mao, K.-X. Lu and J.-M. Bai (YNAO, CAS) report:
We observed the field of GRB 240821A, reported by Fermi/GBM (GCN 37219, GCN 37239), SVOM/ECLAIRs (GCN 37220, T0 at 2024-08-21T18:35:50.150), GRANDMA/LesMakes-T60 (GCN 37225), SVOM/GRM (GCN 37226), EP/FXT (GCN 37230) and Swift ToO (GCN 37236), using the GMG-2.4m telescope at Lijiang Observatory.
The observation began at 2024-08-22T16:10:10, about 21.57 hours after the SVOM/ECLAIRs trigger.
No new reliable optical counterpart was detected in the 2x600s stacked image within the 10-arcsec EP/FXT error circle of the afterglow candidate EP J233704.9-101126 (Turpin et al., GCN 37230), down to a 5-sigma limiting magnitude of R ～ 19.6, derived from calibration against the USNO-A2.0 field stars.
The detection limit was relatively shallow because of the lunar phase and the angular distance between the target and the Moon.