TITLE:   GCN CIRCULAR
NUMBER:  37926
SUBJECT: GRB 241025A (EP241025a): Optical afterglow observations with the Tsinghua-Nanshan Optical Telescope
DATE:    24/10/28 14:07:49 GMT
FROM:    Xiaofeng Wang at Tsinghua University <wang_xf@mail.tsinghua.edu.cn>

X. F. Wang (THU), A. Iskandar（XAO), J. L. Liu (THU)，L. T. Wang (XAO), J. Mo (THU), Y.S. Yan (THU), S. Antier (OCA)，and W. X. Li (NAOC) report the optical detections of the afterglow of GRB 241025A/EP241025a (Ambrosi et al., GCN 37859; Fermi GBM team, GCN 37860; Jiang et al., GCN 37862; Wang et al., GCN 37863; Li et al., GCN 37864; Pereyra et al., GCN 37865; Xu et al., GCN 37866; Lipunov et al., GCN 37873; Abdi et al., GCN 37882).

We obtained 300sx9 (~12.8 hrs after the burst) and 100sx30 (~13.3 hrs after the burst) r-band images with the 80~cm Tsinghua-Nanshan Optical Telescope (TNOT) located at Nanshan Station of Xinjiang Astronomy Observatory. The afterglow is clearly detected on the stacked images, with the following magnitudes:
 
r = 21.12 +- 0.08 mag (MJD = 60608.60)
r = 21.17 +- 0.10 mag (MJD = 60608.62)

The above photometric results are calibrated using the field stars from the Pan-STARRS1 catalog and are not corrected for the Galactic extinction. 