[vsnet-grb-info 28010] GRB 210602A: MAXI/GSC detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  30113
SUBJECT: GRB 210602A: MAXI/GSC detection
DATE:    21/06/02 12:44:38 GMT
FROM:    Motoko Serino at Aoyama Gakuin U.  <serino at phys.aoyama.ac.jp>

M. Serino, S. Sugita (AGU),
H. Negoro, M. Nakajima, K. Kobayashi, K. Asakura, K. Seino (Nihon U.),
T. Mihara, T. Tamagawa, M. Matsuoka (RIKEN),
T. Sakamoto, K. Komachi, A. Yoshida (AGU),
Y. Tsuboi, W. Iwakiri, H. Kawai, Y. Okamoto, S. Kitakoga (Chuo U.),
M. Shidatsu (Ehime U.),
N. Kawai, M. Niwano, R. Hosokawa (Tokyo Tech),
S. Nakahira, Y. Sugawara, S. Ueno, H. Tomida, M. Ishikawa, M. Tominaga, T. Nagatsuka (JAXA),
Y. Ueda, S. Yamada, S. Ogawa, K. Setoguchi, T. Yoshitake, Y. Goto, R. Uematsu (Kyoto U.),
H. Tsunemi (Osaka U.),
M. Yamauchi, Y. Nonaka, T. Sato, R. Hatsuda, R. Fukuoka (Miyazaki U.), T. Kawamuro (UDP/NAOJ),
K. Yamaoka (Nagoya U.),
Y. Kawakubo (LSU),
M. Sugizaki (NAOC) 
report on behalf of the MAXI team:

The MAXI/GSC nova alert system triggered a bright uncatalogued 
X-ray transient source at 12:04:02 UT on 2021 June 2.
Assuming that the source flux was constant over the transit,
we obtain the source position at
(R.A., Dec) = (44.630 deg, -2.672 deg) = (02 58 31, -02 40 19) (J2000)
with a statistical 90% C.L. elliptical error region
with long and short radii of 0.17 deg and 0.16 deg, respectively.
The roll angle of long axis from the north direction is 107.0 deg counterclockwise.
There is an additional systematic uncertainty of 0.1 deg (90% containment radius).
The X-ray flux averaged over the scan was 393 +- 52 mCrab
(4.0-10.0keV, 1 sigma error).
Without assumptions on the source constancy, we obtain a rectangular error
box for the transient source with the following corners:
(R.A., Dec) = (43.754, -3.549) deg = (02 55 00, -03 32 56) (J2000)
(R.A., Dec) = (44.013, -3.735) deg = (02 56 03, -03 44 05) (J2000)
(R.A., Dec) = (45.446, -1.751) deg = (03 01 47, -01 45 03) (J2000)
(R.A., Dec) = (45.187, -1.565) deg = (03 00 44, -01 33 53) (J2000)
There was no significant excess flux in the previous transit at 10:31 UT
with an upper limit of 20 mCrab.