TITLE:   GCN CIRCULAR
NUMBER:  45641
SUBJECT: GRB 260918A: SVOM/C-GFT optical upper limits
DATE:    26/09/19 08:55:02 GMT
FROM:    SVOM_group <svomgroup@bao.ac.cn>

Y.Y. Shi (GXU), Z. Kang (CHO), C. Wu , L.P. Xin, X.H. Han, P.P. Zhang, X.M. Lu (NAOC), Z.W. Li, Y. Lv (CHO), R.S. Zhang, Y.J. Xiao, Y.L. Qiu, J. Wang, J.S. Deng, L. Huang, J.Y. Wei (NAOC), Yun Wang (UCB; PMO), Yehao Cheng(YNU) report on behalf of the SVOM/C-GFT team:

 
We observed the field of GRB 260918A detected by SVOM/Eclairs (Zhao et al., GCN 45619) with LATIOS on SVOM/C-GFT. Our observations started at 2026-09-18T16:11:08 UTC, ~ 12.39 hr after the trigger. 
 
We obtained follow-up imaging in g, r, and i bands. After preliminary analysis, no credible candidate was detected within the error box of source #1 and #2 provided by EP-FXT (Zou et al., GCN 45632) in our images. We measure the following upper limits calibrated against the Pan-STARRS DR1 catalog, and not corrected for Galactic extinction:
 
g > 20.5 AB (3-sigma, mid-time 13.56 hr after the trigger).
r > 21.1 AB (3-sigma, mid-time 13.24 hr after the trigger).
i > 20.5 AB (3-sigma, mid-time 12.67 hr after the trigger).
 
Our non-detection is consistent with the non-detections by Méndez et al. (GCN 45620), Yin et al. (GCN 45622), Li et al. (GCN 45634). 

We note that in source #3 position of EP/FXT (Zou et al., GCN 45632), a known optical source (GR*244: Double or Multiple Star) is bright in PS1 DR1; in source #4 position, a known optical source (6dFGS gJ233834.0-090039 : Seyfert 1 Galaxy) is ~0.6 mag brighter than in the catalogue in b band.


We thank the observation assistants C.-L. Guo and Y.-H. Hao at Jilin observatory for their excellent support.
 
The Chinese Ground Follow-up Telescope (C-GFT) for the SVOM mission is located at Jilin Station, Changchun Observatory, National Astronomical Observatories, CAS. It features two instruments: (1) CATCH at the Cassegrain focus with a 21 arcmin x 21 arcmin FOV for simultaneous g/r/i-band imaging, and (2) LATIOS, a 4k x 4k CMOS camera at the prime focus with a 1.28 deg x 1.28 deg FOV that images in g, r, and i bands via filter switching.