TITLE:   GCN CIRCULAR
NUMBER:  35483
SUBJECT: GRB 240101B: 1.3m DFOT optical upper limit
DATE:    24/01/05 11:17:13 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 the GRB 240101B detected by Swift (Cenko et al.
2024, GCN 35449) 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 12:43:55 UT, i.e., ~ 0.68 days 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
(Evans et al., 2024, GCN 35455). We obtain the following preliminary
3-sigma upper limit in the stacked image:

Date Start_UT T_start-T0 (days) Filter  Exp time (s)  Limiting magnitude
=========================================================
2024-01-02 12:43:55    ~0.68      R     300*12       > 21.7


Our non-detection is consistent with Zheng et al. 2024, GCN 35454; Kuin et
al. 2024, GCN 35458; and Peretto 2024, GCN 35463.

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.