[vsnet-grb-info 27833] GRB 210504A: MITSuME Akeno optical upper limits

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  29936
SUBJECT: GRB 210504A: MITSuME Akeno optical upper limits
DATE:    21/05/04 23:35:54 GMT
FROM:    Ryohei Hosokawa at Tokyo Institute of Technology  <hosokawa at hp.phys.titech.ac.jp>

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

We observed the field of GRB 210504A (Beardmore et al. GCN Circular #29929, Lien
 et al. GCN Circular #29930) with the optical three color (g', Rc, and
Ic) CCD cameras attached to the MITSuME 50 cm telescope of Akeno
Observatory, Yamanashi, Japan. The observation with a series of 60 sec
exposures started at 2021-05-04 14:55:16 UT (1.0 hour after the BAT
trigger, Lien et al. GCN Circular #29930). We stacked the images with
good conditions. We did not detect any uncatalogued sources within the
XRT error circle (Beardmore et al. GCN Circular #29929) 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
------------------------------------------------------------------------------------------------
1.1 2021-05-04 15:01 300 g’>15.9, Rc>16.2, Ic>15.9
2.8 2021-05-04 16:42 2580 g’>18.3, Rc>18.7, Ic>18.3
------------------------------------------------------------------------------------------------
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).