TITLE: GCN CIRCULAR NUMBER: 33269 SUBJECT: GRB 230204B: GIT discovery of the likely optical afterglow DATE: 23/02/05 05:46:49 GMT FROM: Harsh Kumar at Indian Inst of Tech,Bombay V. Swain (IITB), H. Kumar (IITB), G. Waratkar(IITB), V. Bhalerao (IITB), G. C. Anupama(IIA), S. Barway (IIA) and K. Angail (IAO) report on behalf of the GIT team: We observed the field of GRB 230204B detected by MAXI (Serino et al., GCN 33265) with 0.7m GROWTH-India Telescope (GIT). We started observations at 23:22:37.597 UT, i.e., 1.57 hrs after the Swift/BAT trigger. We obtained 10 frames in the r' band of 300 sec each. We detected an uncatalogued source at RA 13:10:34.96, Dec: -21:43:05.31 with an uncertainty of 0.67 arcsec. There is no minor planet present at this position. The photometric results follow as: ---------------------------------------------------------------------- JD (mid) | T_mid-T0 (hrs) | Filter | Magnitude (AB) | ---------------------------------------------------------------------- 2459980.47404 | 1.57 | r' | 15.50 +/- 0.04 | 2459980.50774 | 2.38 | r' | 16.45 +/- 0.05 | ---------------------------------------------------------------------- The candidate decayed by 0.95 magnitude during our observations, separated by a time span of 48 mins. The fast decay suggests that the candidate is likely an afterglow of GRB 230204B. We encourage photometric for further confirmation and spectroscopic follow-up for redshift measurement. The magnitudes are calibrated against PanSTARRS DR1 (Chambers et al., 2016) and not corrected for Galactic extinction. The GROWTH India Telescope (GIT; Kumar et al. 2022) 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/.