[vsnet-grb-info 27572] GRB 210318B: MITSuME Okayama optical upper limits

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  29675
SUBJECT: GRB 210318B: MITSuME Okayama optical upper limits
DATE:    21/03/20 02:11:32 GMT
FROM:    Ryohei Hosokawa at Tokyo Institute of Technology  <hosokawa at hp.phys.titech.ac.jp>

R. Hosokawa, K. L. Murata, R. Adachi, M. Niwano, F. Ogawa, N.Nakamura,
N. Ito, S. Ogata, H. Takamatsu, H. Hara, Y. Yatsu, and N.Kawai
(TokyoTech) report on behalf of the MITSuME collaboration:

We observed the field of GRB 210318B (Troja et al. GCN Circular
#29663, Svinkin et al. GCN Circular #29664, Stamatikos et al. GCN
Circular #29666, Lipunov et al. GCN Circular #29667, Malacaria et al.
GCN Circular #29668) with the optical three color (g', Rc, and Ic) CCD
cameras attached to the MITSuME 50 cm telescope of Okayama
Astrophysical Observatory, Okayama, Japan. The observation with a
series of 60 sec exposures started at 2021-03-19 19:11:03 UT.(40.4
hours after Swift BAT trigger) We stacked the images with good
conditions. We did not find any new point sources within the Swift XRT
circle (Troja et al. GCN Circular #29663) in all three bands.
We obtained the 5-sigma limits of the stacked images as follows.

T0+[hour] MID-UT T-EXP[sec] 5-sigma limits
------------------------------------------------------------------------------------------------
40.4 19:50:32 2040 g'>14.3, Rc>14.2, Ic>13.4
------------------------------------------------------------------------------------------------
T0+ : Elapsed time after the burst
T-EXP: Total Exposure time
We used the UCAC4 catalog for flux calibration.
The magnitudes are expressed in the AB system.
The images were processed in real-time through the MITSuME GPU
reduction pipeline (Niwano et al. 2021, PASJ, Vol.73, Issue 1, Pages
4-24; https://github.com/MNiwano/Eclaire).