[vsnet-grb-info 20924] GRB 180721A: MITSuME Akeno optical upper limits

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  23022
SUBJECT: GRB 180721A: MITSuME Akeno optical upper limits
DATE:    18/07/23 09:52:13 GMT
FROM:    Ryosuke Itoh at Tokyo Institute of Tech.  <itoh at hp.phys.titech.ac.jp>

M. Oeda, R. Itoh, K. L. Murata, Y. Tachibana, S. Harita, K. Morita,
K. Shiraishi, K. Iida, R. Adachi, S. Niwano,
Y. Yatsu, and N. Kawai (Tokyo Tech)
report on behalf of the MITSuME collaboration:

We searched for the optical counterpart of GRB 180721A
(B. Sbarufatti et al., GCN Circular #22994)
with the optical three color (g', Rc, and Ic) CCD cameras attached to
the MITSuME 50cm telescope of Akeno Observatory, Yamanashi, Japan.

The observation started on 2018-07-21 13:44:45.05 UT.
We did not find any point source at the enhanced position of the
XRT error circle (M.R. Goad et al., GCN Circular #22997) in all three bands.
We obtained following 5-sigma upper limits for the magnitudes.

T0+[min]    MID-UT      T-EXP[sec]    g'       Rc        Ic
-------------------------------------------------------------------------------------------------------
157.95     14:27:28  4,740   >16.9   >17.3   >16.9
-------------------------------------------------------------------------------------------------------
T0+ : Elapsed time after the burst
T-EXP: Total Exposure time
We used UCAC-4 catalog for flux calibration.