[vsnet-grb-info 27757] GRB 210413B: MITSuME Okayama optical upper limits

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  29860
SUBJECT: GRB 210413B: MITSuME Okayama optical upper limits
DATE:    21/04/21 09:41:19 GMT
FROM:    Naohiro Ito at Tokyo Tech  <n.ito at hp.phys.titech.ac.jp>

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

We observed the field of GRB 210413B (Fermi/GBM TRIGGER 640050417, P.
A. Evans et al. GCN Circular #29821, Gregory S.H. Paek et al. GCN
Circular #29825, J.A. Kennea et al. GCN Circular #29827) with the
optical three color (g', Rc, and Ic) CCD cameras attached to the
MITSuME 50 cm telescope of Okayama Astronomical Observatory, Okayama,
Japan. The observation with a series of 60 sec exposures started at
2021-04-17 13:31:10 UT (85.8 hours after the Fermi/GBM trigger
640050417). We stacked the images with good conditions. We did not
find any transients within the BAT error region (A. Tohuvavohu et al.
GCN Circular #29819) 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
------------------------------------------------------------------------------------------------
86.8 15:06 2340 g'>17.4, Rc>17.6, Ic>17.3
------------------------------------------------------------------------------------------------
T0+ : Elapsed time after the burst
T-EXP: Total Exposure time
We used the PS1 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).