GRB 221009A / Swift J1913.1+1946: GIT detection of the optical afterglow

We observed Swift J1913.1+1946/GRB 221009A detected by Swift (S. Dichiara et al., GCN #32632), Fermi (P. Veres et al., GCN #32636), INTEGRAL (SPI-ACS) (Gotz et al., GCN #32660), and Konus-Wind (D. Svinkin et al., GCN #32641), with 0.7m GROWTH-India Telescope (GIT). We obtained 200-sec exposures in the g' and r' filters. We clearly detected the afterglow candidate in our images at the position of Swift J1913.1+1946/GRB 221009A. The photometric results follow as: ------------------------------------------------------------------- JD (mid) | T_mid-T0(hrs) | Filter | Magnitude (AB) | ------------------------------------------------------------------- 2459862.18181 | 2.19 | g' | 17.66 +/- 0.07 | 2459862.18451 | 2.25 | r' | 16.16 +/- 0.07 | ------------------------------------------------------------------- The results are consistent with Lipunov et al., GCN #. 32634 and 32639; Perley GCN #32638; Broens, GCN #32640; Hu et al., GCN #32644; Belkin et al. GCN #32645; de Wet et al. GCN #32646; Xu et al. GCN #32647; Odeh, GCN #32649; Brivio et al. GCN # 32652. The magnitudes are calibrated against PanSTARRS DR1 (Chambers et al., 2016) 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 (IIA) and the Indian Institute of Technology Bombay (IITB) with funding from DST-SERB and IUSSTF. It is located at the Indian Astronomical Observatory (Hanle), operated by IIA. We acknowledge funding by the IITB alumni batch of 1994, which partially supports the operations of the telescope. Telescope technical details are available at https://sites.google.com/view/growthindia/.