Skip to main content
Introducing Einstein Probe, Astro Flavored Markdown, and Notices Schema v4.0.0. See news and announcements

GCN Circular 29237

GRB 210104A: MITSuME Akeno optical observation
2021-01-04T12:44:41Z (4 years ago)
Ryohei Hosokawa at Tokyo Institute of Technology <>
R. Hosokawa, R. Adachi, M. Niwano, K. L. Murata, 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 210104A (The Fermi GBM team
, GCN 29232, E. Troja et al., GCN 29233, B. Biltzinger et al., GCN 29234) 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 started at 2021-01-04 11:27:54 UT (55s after Swift BAT
trigger). We detected the point source at the position consistent with
the afterglow detected previously(E. Troja et al., GCN 29233, L. P.
Xin et al., GCN 29235, Y.-D. Hu et al., GCN 29236).
We measured the magnitudes as follows.

T0+[sec] MID-UT T-EXP[sec] measured magnitudes
55 11:28:24 60 g'=14.6+/-0.1, Rc=14.2+/-0.1, Ic=13.8+/-0.1
T0+ : Elapsed time after the burst
T-EXP: Total Exposure time

We used 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.,,;
Looking for U.S. government information and services? Visit