[vsnet-grb-info 28378] GRB 210722A: GIT optical detection and preliminary analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  30481
SUBJECT: GRB 210722A: GIT optical detection and preliminary analysis
DATE:    21/07/23 13:44:05 GMT
FROM:    Harsh Kumar at Indian Inst of Tech,Bombay  <harshkosli13 at gmail.com>

H. Kumar(IITB), S. Joharle (Fergusson College), J. Stanzin (IAO), V.
Bhalerao(IITB), G. C. Anupama(IIA), S. Barway(IIA) report on behalf of the GIT
team:

We observed GRB 210722A detected by Swift Burst Alert Telescope (P.
D'Avanzo et al., GCN #30475) and optical afterglow detected by P. D'Avanzo
et al., GCN #30475; Z.P. Zhu et al., GCN #30476; N. Pankov et al., GCN
#30477; with 0.7m GROWTH-India Telescope (GIT). We obtained multiple
exposures in the g', r' filters. The image depth was shallower than usual
due to weather conditions. We clearly detected the afterglow in our images
at R.A.= 1:48:07.29, DEC.= -6:20:49.85, which agrees with the swift UVOT
position (GCN #30475). The photometric results follow as:

------------------------------------------------------------------------

T_start - T0 (days) | Exposure (sec) | Filter | Magnitude (AB)| Notes |

------------------------------------------------------------------------

 0.014938 | 100  | g' | 15.95 +/- 0.23 | Low significance detection

 0.012057 | 100  | r' | 15.11 +/- 0.08 |

 0.032546 | 4x100 | r' | 16.34 +/- 0.08 | Stacked image

 0.050742 | 100  | r' | 16.81 +/- 0.19 |

 0.053035 | 100  | r' | 16.88 +/- 0.07 |

 ------------------------------------------------------------------------

Based on our observations, we found that the GRB is decaying with a
power-law index of 1.14 +/- 0.03 in r' band. Our observations are in
agreement with magnitudes reported by Z.P. Zhu et al., GCN #30476, and N.
Pankov et al., GCN #30477. The magnitudes are calibrated against PanSTARRS
(Flewelling et al., 2018) and not corrected for Galactic extinction.

The GROWTH India Telescope (GIT) is a 70-cm telescope with a 0.7-degree
field of view, set up by the Indian Institute of Astrophysics and the
Indian Institute of Technology Bombay with support from the Indo-US Science
and Technology Forum (IUSSTF) and the Science and Engineering Research
Board (SERB) of the Department of Science and Technology (DST), Government
of India (https://sites.google.com/view/growthindia/). It is located at the
Indian Astronomical Observatory (Hanle), operated by the Indian Institute
of Astrophysics (IIA).