TITLE:   GCN CIRCULAR
NUMBER:  35484
SUBJECT: GRB 240102A: 1.3m DFOT optical upper limit
DATE:    24/01/05 11:20:00 GMT
FROM:    Amit Kumar Ror at ARIES <mitturor77894@gmail.com>

Amit K. Ror, Rahul Gupta, Amar Aryan, and Shashi B. Pandey (ARIES) report:

We observed the field of GRB 240102A detected by Swift (Gropp et al. 2024,
GCN 35461) 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
2024-01-02 at 18:23:56 UT, i.e., ~ 49 minutes after the BAT trigger. We
have taken multiple frames with an exposure time of 300 s in the R filter.
We stacked the images after the alignment. We did not detect any optical
afterglow in our stacked image within the enhanced Swift-XRT error box
(Goad et al., 2024, GCN 35471). We obtain the following preliminary 3-sigma
upper limit in the stacked image:


Date Start_UT T_start-T0 (minutes) Filter  Exp time (s)  Limiting magnitude
=========================================================
2024-01-02 18:23:56    ~49     R     300*20     > 21.5


Our non-detection is consistent with the observations of Hu et al. 2024,
GCN 35465; Strausbaugh et al. 2024, GCN 35467; and Belles et al. 2024, GCN
35475.

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 catalog. This circular may be cited.