TITLE:   GCN CIRCULAR
NUMBER:  46047
SUBJECT: GRB 261026A: J-band observations by the SYSU 80cm infrared telescope
DATE:    26/10/26 16:43:15 GMT
FROM:    shiy228@mail2.sysu.edu.cn

Yun Shi, Jin-Ji Li, Shu-Quan Bai, Jian-Hong Cao, Zhong-Nan Dong, Rui-Chen Gao, Si-Rui Huang, Jia-Qi Lin, Pu Lin, Jing-Kai Sun, Zhi-Xiang Tan, Lu-Yao Wen, Hao-Nan Yang, Hao-Ran Zhang, P. H. Thomas Tam, Rong-Feng Shen, and Bin Ma (Sun Yat-sen University) report on behalf of the SYSU 80cm infrared telescope team: 

We observed the field of GRB 261026A, detected by SVOM/ECLAIRs (Goto et al., GCN 46030), using the Sun Yat-sen University (SYSU) 80 cm infrared telescope in the J band. Our observations were carried out on 2026 Oct 26 from 11:50:00 to 12:50:00 UT (from ~5.67 to ~6.67 hours after the SVOM/ECLAIRs trigger), using stacked images in the J band (165 x 20 s, 3300 s total exposure).

We clearly detect the near-infrared afterglow at the position of the previously reported optical counterpart (Dornic et al., GCN 46033; Zheng et al., GCN 46034; Mohan et al., GCN 46041; Li et al., GCN 46046), and we measure a magnitude of:
J = 19.37 +/- 0.14 mag (Vega), at a mid-time of ~6.17 hours post-trigger.

Assuming a standard J-band conversion of J (AB) = J (Vega) + 0.91, our measurement corresponds to J ~ 20.28 mag (AB). Comparing this with the early J-band detection by WINTER (J = 18.55 +/- 0.1 mag, AB, at T0+12.6 min; Mohan et al., GCN 46041), our result indicates a significant fading of ~1.73 mag over ~6 hours. 

The photometry was calibrated against nearby stars from the 2MASS catalog and is reported in the Vega system, without correction for Galactic extinction.

The SYSU 80 cm infrared telescope is operated and managed by the Department of Astronomy, Sun Yat-sen University.