{
  "bibcode": "2021GCN.29759....1S",
  "body": "F. Sutaria (IIA, Bangalore, India) and A. Ray (TIFR /HBCSE, Mumbai, \nIndia) report on the observations of the optical counterpart of GRB \n210207B (Lien et al., GCN #29420; Strausbaugh, R, GCN #29441 and \nreferences therein) taken with the Himalyan Chandra telescope (HCT) on \ntwo epochs.\n\nThe first observation was on MJD 59254.91163194 -- i.e 48.0103 hr after \nthe Swift/BAT trigger.  The field of the GRB was observed in the Bessel \nR filter.  We stacked 12 frames to achieve a total exposure time of 570 \ns. The photometry  was carried out using standard  IRAF utilities for \nfaint objects in relatively uncrowded fields. The instrumental \nmagnitudes were calibrated against photometric  standards in the field \nof PG0918+029, taken on the same and on the previous night, resulting in \nan average atmospheric extinction coefficient of 0.087(\\pm 0.0208) /mag \nin this filter. At the position of the GRB  (18:02:32.40 +53:40:56.0) we \nfind a faint optical source with apparent magnitude R=22.0 \\pm 0.1, \nuncorrected for galactic extinction.\n\n\nWe observed the same field once again on 17th Mar. 2021 (MJD \n59290.91730324), in the same filter. A stacked exposure of 10 frames \nleading to a total exposure time of 600s  did not reveal any source at \nthe location of the GRB, down to a 3-sigma limiting magnitude of R= \n23.66. We thus conclude that there was no contribution from the host \ngalaxy in the previous detection. Our results are also tabulated below.\n\n-------------------------------------------------------------------------------\n-------------------------------------------------------------------------------\nMJD            Filter  Detected?         Magnitude\n                                          (uncorrected for galactic \nextinction)\n-------------------------------------------------------------------------------\n59254.9116        R        Yes           22.0 \\pm 0.1\n59290.9173        R        No.           < 23.66 (3-sigma)\n-------------------------------------------------------------------------------\n\nWe note that the galactic extinction for the CTIO R filter in this \ndirection is estimated at A_R = 0.087 mag [Schlafly E. F. & Finkbeiner \nD., 2011, ApJ, 737, 103], based on a SDSS dust map. However, the IRAS \nand COBE/DIRBE survey  [D.J. Schlegel, D.P. Finkbeiner, & M. Davis, \n1998, ApJ, 500, 525] sets it at A_R=0.109 mag.\n\nThis GCN may be cited.\n\nWe thank the staff of IAO, Hanle and CREST, Hosakote, that made these \nobservations possible. The facilities at IAO and CREST are operated by \nthe Indian Institute of Astrophysics, Bangalore.",
  "circularId": 29759,
  "createdOn": 1617555036000,
  "email": "fsutaria@iiap.res.in",
  "subject": "GRB 210207B: Prompt and very late time observations with HCT.",
  "submitter": "Firoza Sutaria at Indian Inst. of Astrophysics  <fsutaria@iiap.res.in>",
  "eventId": "GRB 210207B"
}