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 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).