GRB 240825A: GMG Optical Observation

We observed the field of GRB 240825A (Gupta et al., GCN 37274, T0 at 2024-08-25T15:52:59) using the GMG-2.4m telescope at the Lijiang Observatory. The observation began at 2024-08-25T17:42:38, about 1.83 hours after the trigger. The optical counterpart of GRB 240825A, not visible in the Pan-STARRS1 r-band image, was clearly detected at the coordinates (J2000): RA = 22h58m17.26s DEC = +01d01'36.7" , with a positional uncertainty of 0.5" or better. The position is consistent with Swift/UVOT (GCN 37274), Nanshan/HMT (GCN 37275), Skynet (GCN 37276) and AKO (GCN 37277). The preliminary analysis results are shown as follows: +----------------+------------+----------+--------------+----------------+ | Tmid-T0 [hr] | Exp. [s] | Filter | Mag | 5-sigma U.L. | +================+============+==========+==============+================+ | 1.91 | 600 | R | 18.97 ± 0.04 | 21 | +----------------+------------+----------+--------------+----------------+ 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) = 0.053 mag in the direction of the optical counterpart (Schlafly & Finkbeiner 2011). The optical spectroscopic observation is ongoing, but there are thin clouds in the sky. We acknowledge the staff at the Lijiang Observatory for their efforts in conducting the observation. In particular, we extend our gratitude to the on-duty observers for promptly resolving the instrumental cooling problems with the GMG-2.4m telescope that arose during the night.