TITLE: GCN CIRCULAR NUMBER: 30163 SUBJECT: GRB 210610A: GIT optical detection DATE: 21/06/10 16:57:26 GMT FROM: Harsh Kumar at Indian Inst of Tech,Bombay H. Kumar(IITB), V. Bhalerao(IITB), U. Stanzin (IAO), G. C. Anupama(IIA), S. Barway(IIA) report on behalf of the GIT team: We observed GRB 210610A detected by Swift-BAT ( K. L. Page et al., GCN #30160, optical counterpart reported by R. Hosokawa et al., GCN #30161 and D. Xu et al., GCN #30162), with the 0.7m GROWTH-India Telescope (GIT). We obtained a 300-sec exposure in the r' filter. We clearly detected the afterglow in our image at R.A.= 13:37:07.64 and DEC.= 14:27:55.10. The photometric results follow as: ------------------------------------------------------------------- JD (start) | T_mid-T0(hrs) | Filter | Magnitude (AB) | ------------------------------------------------------------------- 2459376.178 | 1.22 | r' | 18.79+/- 0.05 | ------------------------------------------------------------------- The magnitudes are calibrated against PanSTARRS DR1 (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).