TITLE: GCN CIRCULAR NUMBER: 30174 SUBJECT: GRB 210610B: GIT optical detection DATE: 21/06/10 20:45:52 GMT FROM: Harsh Kumar at Indian Inst of Tech,Bombay H. Kumar(IITB), J. Stanzin (IAO), V. Bhalerao(IITB), G. C. Anupama(IIA), S. Barway(IIA) report on behalf of the GIT team: We observed GRB 210610B detected by Swift-BAT (K. L. Page et al., GCN #30170), with the 0.7m GROWTH-India Telescope (GIT). We obtained a 60-sec exposure in the r' filter. We clearly detected the afterglow in our image at R.A.= 16:15:40.44 and DEC.= +14:23:56.65 with an uncertainty of ~0.67 arcsec. The photometric results follow as: ------------------------------------------------------------------- JD (start) | T_mid-T0(hrs) | Filter | Magnitude (AB) | ------------------------------------------------------------------- 2459376.3429 | 0.37 | r' | 15.98 +/- 0.1 | ------------------------------------------------------------------- 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).