[vsnet-grb-info 26702] GRB 201027A: MITSuME Akeno optical upper limits

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  28802
SUBJECT: GRB 201027A: MITSuME Akeno optical upper limits
DATE:    20/10/29 01:29:33 GMT
FROM:    Ryohei Hosokawa at Tokyo Institute of Technology  <hosokawa at hp.phys.titech.ac.jp>

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

We observed the field of GRB 201027A (V. Lipunov et al., GCN #28787,
S. B. Cenko et al., GCN #28788, Y.-D. Hu et al., GCN #28794 ) 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 2020-10-27
18:43:12 UT(17.2 hour after trigger). Since the first 18 images were
taken under high airmass conditions, we stacked the images with good
conditions. We did not find any new point sources within the enhanced
Swift/XRT circle (J.P. Osborne et al., GCN #28792) 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
------------------------------------------------------------------------------------------------
17.6 19:19:32 3180 g'>19.5,Rc>20.0,Ic>19.1
------------------------------------------------------------------------------------------------
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.,
https://doi.org/10.1093/pasj/psaa091,
https://arxiv.org/abs/2008.11486; https://github.com/MNiwano/Eclaire).