TITLE:   GCN CIRCULAR
NUMBER:  38875
SUBJECT: GRB 250108B: 1.3m DFOT upper limit
DATE:    25/01/09 16:23:09 GMT
FROM:    Amit Kumar Ror at ARIES <mitturor77894@gmail.com>

Amit K. Ror, Anshika Gupta, RKS Yadav, Shashi B. Pandey, Kuntal Mishra
(ARIES) report:

We observed the field of GRB 250108B detected by Swift (Swift Observatory
Team, Klingler et al. 2025, GCN 38847) with the 1.3m Devasthal Fast Optical
Telescope (DFOT), located at the Devasthal Observatory of the Aryabhatta
Research Institute of Observational Sciences (ARIES), India. The
observations were started on 2025-01-08 at 21:58:57 UT, i.e., ~ 0.48 days
after the Swift-BAT trigger. We have taken multiple frames with an exposure
time of 300s in the R filter. We stacked the images after the alignment. We
could not detect the optical emission reported by Rastinejad et al. (2025,
GCN 38855) in our stacked image within the error box enhanced Swift-XRT
position (Osborne et al. 2025, GCN 38848). We obtain the following 3-sigma
upper limit in the stacked image:

Date Start_UT T_start-T0 (days) Filter  Exp time (s)  Magnitude
=========================================================
2025-01-08 21:58:57    ~ 0.48     R     300s*12     >21.8

The non-detection of the burst is consistent with the upper limits reported
by Breeveld et al. 2025, GCN 38850 and Lipunov et al. 2025, GCN 38858.

The magnitude is not corrected for the Galactic extinction in the direction
of the burst. Photometric calibration is performed using the standard stars
from the USNO-B1.0 catalogue. This circular may be cited.