[vsnet-grb-info 27138] GRB 210104A: MITSuME Ishigaki optical observation

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  29241
SUBJECT: GRB 210104A: MITSuME Ishigaki optical observation
DATE:    21/01/04 20:02:05 GMT
FROM:    Takashi Horiuchi at Ishigakijima Astronomical Obs  <takashi.horiuchi at nao.ac.jp>

Takashi Horiuchi, Hidekazu Hanayama (NAOJ), Katsuhiro L. Murata,
Yoichi Yatsu, Nobuyuki Kawai (Tokyo Tech) report on behalf of the
MITSuME collaboration:

We observed the field of GRB 210104A (The Fermi GBM team,
GCN 29232, E. Troja et al., GCN 29233) with the optical three
color (g', Rc, and Ic) CCD cameras attached to the 105 cm
Murikabushi telescope of Ishigakijima Astronomical Observatory,
Okinawa, Japan.

The observation with a series of 60 sec exposures started on
2021-01-04 13:58:34 UT (150 min after Swift BAT trigger).
We detected the point source at the position consistent with
the afterglow reported by Swift UVOT and obtained the
magnitudes as follows.

T0+[min] MID-UT T-EXP[sec] measured magnitudes
------------------------------------------------------------------------------------------------
150 2021-01-04T14:14:02 1500  g'=19.17+/-0.08, Rc=18.12+/-0.04, Ic=17.96+/-0.09
------------------------------------------------------------------------------------------------
T0+ : Elapsed time after the burst
T-EXP: Total Exposure time
The SDSS catalog (DR16) is used for flux calibration.