GCN Circular 40032
Subject
GRB 250403A: GMG Optical Observation
Event
Date
2025-04-03T17:52:32Z (3 months ago)
From
Rui-Zhi Li at Yunnan Observatories, CAS <liruizhi@ynao.ac.cn>
Via
Web form
R.-Z. Li, B.-T. Wang, F.-F. Song, J. Mao, H.-C. Feng and J.-M. Bai (YNAO, CAS) report:
We observed the field of GRB 250403A (Fermi/GBM team, GCN 40025, T0 at 2025-04-03T15:15:22; Julakanti et al., GCN 40026) using the GMG-2.4m telescope at the Lijiang Observatory. The observation began at 2025-04-03 17:24:07, about 2.15 hours after the trigger.
The optical counterpart of GRB 250403A (Starling et al., GCN 40028; Wu et al., GCN 40029; Du et al., GCN 40031) was clearly detected in the r-band image with an exposure of 600 s.
The preliminary analysis results are shown as follows:
+---------------+------------+----------+--------------+----------------+
| Tmid-T0 [h] | Exp. [s] | Filter | Mag | 5-sigma U.L. |
+===============+============+==========+==============+================+
| 2.23 | 600 | r | 19.23 ± 0.03 | 21.6 |
+---------------+------------+----------+--------------+----------------+
The given magnitudes are derived based on calibration against Pan-STARRS1 field stars, and are not corrected for the expected Galactic foreground extinction, corresponding to a reddening of E(B-V) = 0.1110 mag in the direction of the optical counterpart (Schlafly & Finkbeiner 2011).