[vsnet-grb-info 27993] GRB 210528B: MITSuME Akeno optical upper limits

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  30096
SUBJECT: GRB 210528B: MITSuME Akeno optical upper limits
DATE:    21/05/29 13:57:33 GMT
FROM:    Katsuhiro L. Murata at Nagoya U  <murata at u.phys.nagoya-u.ac.jp>

K. L. Murata, R. Hosokawa, M. Niwano, Y. Imai, N. Ito, H. Takamatsu, 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 210528B (Sugawara et al. GCN Circular #30094,
Lipunov et al. GCN Circular #30095) with the optical three color (g', Rc,
and Ic) CCD cameras attached to the MITSuME telescope Akeno. The
observation with a series of 60 sec exposures started at 2021-05-29
11:21:57 UT (12.5 hours after the trigger). We stacked the images with good
conditions. We did not detect any uncatalogued sources in all three bands
within the elliptical error region (Sugawara et al. GCN Circular #30094)
determined under the assumption that the source flux was constant over the
transit. We obtained the 5-sigma limits of the stacked images as follows.

T0+[hour] MID-UT T-EXP[sec] 5-sigma limits
------------------------------------------------------------------------------------------------
12.5 2021-05-29 12:13 1560 g'>19.9
12.5 2021-05-29 12:13 2040 Rc>20.2
12.5 2021-05-29 12:13 1500 Ic>19.4
------------------------------------------------------------------------------------------------
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).