TITLE: GCN CIRCULAR NUMBER: 28711 SUBJECT: GRB 201020A: GROWTH-India Telescope optical observations DATE: 20/10/21 02:17:35 GMT FROM: Varun Bhalerao at Indian Inst of Tech H. Kumar(IITB), J. Stanzin (IIA), V. Bhalerao(IITB), G. C. Anupama(IIA), S. Barway(IIA), report on behalf of the GROWTH-India collaboration: We followed up GRB 2010210A (E. Ambrosi et al., GCN #28696; also see:- R. Adachi et al., GCN #28697; J.P. Osborne et al., GCN #28698; V. Lipunov et al., GCN #27800, S.Y. Fu et al., GCN #28701; S. Belkin et al., GCN #28703 and T. Pankov et al., GCN #28708) with 0.7m GROWTH-India telescope. We obtained 300-sec exposures in the SDSS r’ filter starting at 2020-10-20T13:00:50.42 UT (~7.22 hrs after the burst). We clearly detected uncataloged sources at a position consistent with E. Ambrosi et al., GCN #28696. Here are the photometric results from GIT observations:- ------------------------------------------------------------------ JD (END) | T_end-T0(hrs) | Filter | Mag | ------------------------------------------------------------------ 2459143.04576 | 7.31 | r | 19.43 +/- 0.06 2459143.04943 | 7.39 | r | 19.49 +/- 0.05 2459143.05670 | 7.57 | r | 19.52 +/- 0.04 2459143.06046 | 7.66 | r | 19.59 +/- 0.04 2459143.06406 | 7.75 | r | 19.63 +/- 0.04 2459143.06764 | 7.83 | r | 19.65 +/- 0.04 ----------------------------------------------------------------- Combining our photometric results with r’ measurements of S.Y. Fu et al., (GCN #28701), S. Belkin et al., (GCN #28703), and T. Pankov et al., (GCN #28708) we conclude that the source is fading with a power-law index of 1.6 +/- 0.2. Given the fast fading, we encourage the follow-up of the source. The magnitudes are 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).