{
  "bibcode": "2021GCN.29241....1H",
  "body": "Takashi Horiuchi, Hidekazu Hanayama (NAOJ), Katsuhiro L. Murata,\nYoichi Yatsu, Nobuyuki Kawai (Tokyo Tech) report on behalf of the\nMITSuME collaboration:\n\nWe observed the field of GRB 210104A (The Fermi GBM team,\nGCN 29232, E. Troja et al., GCN 29233) with the optical three\ncolor (g', Rc, and Ic) CCD cameras attached to the 105 cm\nMurikabushi telescope of Ishigakijima Astronomical Observatory,\nOkinawa, Japan.\n\nThe observation with a series of 60 sec exposures started on\n2021-01-04 13:58:34 UT (150 min after Swift BAT trigger).\nWe detected the point source at the position consistent with\nthe afterglow reported by Swift UVOT and obtained the\nmagnitudes as follows.\n\nT0+[min] MID-UT T-EXP[sec] measured magnitudes\n------------------------------------------------------------------------------------------------\n150 2021-01-04T14:14:02 1500  g'=19.17+/-0.08, Rc=18.12+/-0.04, Ic=17.96+/-0.09\n------------------------------------------------------------------------------------------------\nT0+ : Elapsed time after the burst\nT-EXP: Total Exposure time\nThe SDSS catalog (DR16) is used for flux calibration.",
  "circularId": 29241,
  "createdOn": 1609790525000,
  "email": "takashi.horiuchi@nao.ac.jp",
  "subject": "GRB 210104A: MITSuME Ishigaki optical observation",
  "submitter": "Takashi Horiuchi at Ishigakijima Astronomical Obs  <takashi.horiuchi@nao.ac.jp>",
  "eventId": "GRB 210104A"
}