GCN Circular 21905

D. Kuroda, K. Yanagisawa, Y. Shimizu, H. Toda (OAO, NAOJ),
S. Nagayama (NAOJ), M. Yoshida (Subaru, NAOJ), K. Ohta (Kyoto)
and N. Kawai(Tokyo Tech) report on behalf of MITSuME collaboration:

We observed the field of GRB 170921A (D'Ai et al., GCNC 21901)
with the optical three color (g', Rc and Ic) CCD camera attached
to the MITSuME 50cm telescope of Okayama Astrophysical Observatory.

The observation started on 2017-09-21 14:39:14 UT (~10 min after
the burst). We did not find any new point source within the XRT
error circle (D'Ai et al., GCNC 21901) in all the three bands.

Three sigma upper limits of the OT are listed below.
We used SDSS-DR8 catalog for flux calibration.

#T0+[day]  MID-UT    T-EXP[sec]   g'    Rc     Ic
-----------------------------------------------------
0.04269    15:30:16    5760.0   >20.1  >19.8  >18.8
-----------------------------------------------------
T0+ : Elapsed time after the burst [day]
T-EXP: Total Exposure time [sec]