TITLE:   GCN CIRCULAR
NUMBER:  37928
SUBJECT: GRB 241026A: TNOT optical counterpart detection
DATE:    24/10/28 14:55:01 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), A. Esamdin (XAO), S. Antier (OCA)，and W. X. Li (NAOC) report the optical detections of the afterglow of GRB 241026A/EP241026a with a redshift of 2.79 (Fermi GBM team, GCN 37894; A. Melandri et al., GCN 37896; Yan-Qiu Zhang et al., GCN 37921; D. Y. Li et al., GCN 37909; Shrestha et al., GCN 37913; Moskvitin et al., GCN 37916; Mohan et al., GCN 37918; Moskvitin et al., GCN 37922; Izzo et al., GCN 37925).

We obtained 120sx16 (~16.7 hrs after the GRB detection) r-band and 120sx20 (~17.9 hrs after the GRB detection) i-band images with the 0.8~m 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 = 21.01 +- 0.07 mag (MJD = 60611.14)
i = 20.85 +- 0.08 mag (MJD = 60611.19)

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