[vsnet-grb-info 27466] GRB 210222B: 1.3m DFOT Optical upper limit

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  29569
SUBJECT: GRB 210222B: 1.3m DFOT Optical upper limit
DATE:    21/02/26 06:14:15 GMT
FROM:    Rahul Gupta at ARIES, India  <rahulbhu.c157 at gmail.com>

Rahul Gupta, A. Kumar, Dimple, A. Ghosh, A. Aryan, V. Negi, B. Kumar,
S. B. Pandey, and K. Misra (ARIES) report:

We observed the field of Swift detected GRB 210222B (Gropp et al., GCN
29545) with 1.3m Devasthal Fast Optical Telescope (DFOT) located at
Devasthal observatory of Aryabhatta Research Institute of
Observational Sciences (ARIES), India. The observations were started
on 2021-02-23 at ~ 19:15 UT, i.e., ~ 20.6 hours after the BAT trigger.
We have taken multiple frames having an exposure time of 120 s in the
R and I filters.  We stacked the images after the alignment. We did
not detect the optical afterglow reported previously (Gropp et al. GCN
29545; Hu et al. GCN 29546; Strausbaugh et al. GCN 29547; Mong et al.
GCN 29548, 29550; Perley et al. GCN 29549; Zhu et al. GCN 29551,
Fernandez et al. GCN 29552; Lipunov et al. GCN 29554; Jelinek et al.
GCN 29557; Siegel et al. GCN 29559; Gokuldass et al. GCN 29562; Belkin
et al. GCN 29563; and D'Avanzo et al. GCN 29567) in our stacked image.

We obtain the following 3-sigma upper limit in the stacked image.

Date Start_UT T_start-T0 (hour) Filter  Exp time (s)  Limiting magnitude
====================================================
2021-02-23 19:15   ~20.6          R   120*30      > 21.1



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.