TITLE: GCN CIRCULAR NUMBER: 22012 SUBJECT: GRB 171010A : Optical observations from HCT DATE: 17/10/13 18:11:40 GMT FROM: D.K. Sahu at Indian Inst of Astrophysics,Bangalore GRB 171010A : Optical observations from HCT Brajesh Kumar, D.K. Sahu, G.C. Anupama and Avinash Singh (Indian Institute of Astrophysics, Bangalore, India) communicate on behalf of a larger Indian collaboration. We observed the Fermi LAT GRB 171010A (Omodei et al., GCN 21985) field with the 2-m Himalayan Chandra Telescope (HCT) located at Indian Astronomical Observatory, Hanle, India. Multiple frames in Bessell's R and I bands were obtained starting from 18:43 UT on October 11, 2017. The optical afterglow candidate (Thorstensen and Halpern, GCN 21987; Izzo and  Malesani, GCN 21988; Guidorzi et al., GCN 21991; Malesani et al., GCN 22000; Harita et al., GCN 22001; Breeveld and Siegel, GCN 22004) was detected in our individual frames. The preliminary magnitudes of the OT, calibrated using nearby USNO stars are as follows: -------------------------------------------------------------------   Date          Mid UT      Exp (sec)  Filter   Magnitude   (YYYY-MM-DD)              time -------------------------------------------------------------------   2017-10-11    18:46       300          R      18.31 +/- 0.05   2017-10-11    18:54       300          R      18.38 +/- 0.05   2017-10-11    20:12       450          R      18.42 +/- 0.04   2017-10-11    21:32       300          R      18.48 +/- 0.05   2017-10-11    21:46       300          R      18.51 +/- 0.05 -------------------------------------------------------------------   2017-10-11    20:21       300          I      18.06 +/- 0.05   2017-10-11    20:28       300          I      18.09 +/- 0.05   2017-10-11    21:53       300          I      18.22 +/- 0.05   2017-10-11    22:00       300          I      18.24 +/- 0.05 -------------------------------------------------------------------- Contamination due to the host galaxy has not been removed.