TITLE:   GCN CIRCULAR
NUMBER:  37275
SUBJECT: GRB 240825A: Nanshan/HMT optical afterglow observations
DATE:    24/08/25 16:58:28 GMT
FROM:    Dong Xu at NAOC/CAS <dxu@nao.cas.cn>

S.Q. Jiang, X. Liu, J. An, Z.P. Zhu, S.Y. Fu, D. Xu (NAOC), X. Gao (Urumqi No.1 Senior High School), J.Z. Liu (XAO) report on behalf of a large collaboration:

We observed the field of GRB 240825A detected by Swift (Gupta et al., GCN 37274) and Fermi (Fermi GBM team, GCN 37273), using the HMT-0.5m telescope located at Nanshan, Xinjiang, China. A series of 60 s and 200 s images were obtained in the clear filter, starting at 16:06:38 UT on 2024-08-25, i.e., 819 s after the Swift/BAT trigger.

An uncatalogued and fading optical source is detected in our individual images at coordinates

R.A. (J2000) =  22:58:17.265
Dec. (J2000) = +01:01:36.83

with an uncertainty of ~ 0.4 arcsec, being consistent with the Swift/UVOT position (Gupta et al., GCN 37274). The source has ~ 17.0 mag in our first image, calibrated with Gaia G-band and not corrected for Galactic extinction. We thus think the source is the optical afterglow of the burst. 

Observations are still ongoing.