TITLE:   GCN CIRCULAR
NUMBER:  23103
SUBJECT: GRB 180809A: MAXI/GSC detection
DATE:    18/08/09 12:32:01 GMT
FROM:    Satoshi Nakahira at RIKEN  <nakahira@crab.riken.jp>

F. Yatabe, S. Nakahira, T. Mihara, Y. Takao, M. Matsuoka (RIKEN),
M. Serino, T. Sakamoto,  S. Sugita, Y. Kawakubo, T. Hashimoto, A. Yoshida (AGU),
H. Negoro, M. Nakajima, A. Sakamaki, W. Maruyama (Nihon U.),
N. Kawai, M. Sugizaki, Y. Tachibana, K. Morita (Tokyo Tech),
S. Ueno, H. Tomida, M. Ishikawa, Y. Sugawara, N. Isobe, R. Shimomukai (JAXA),
Y. Ueda, A. Tanimoto, T. Morita, S. Yamada (Kyoto U.),
Y. Tsuboi, W. Iwakiri, R. Sasaki, H. Kawai, T. Sato (Chuo U.),
H. Tsunemi, T. Yoneyama (Osaka U.),
M. Yamauchi, K. Hidaka, S. Iwahori (Miyazaki U.),
T. Kawamuro (NAOJ),
K. Yamaoka (Nagoya U.),
M. Shidatsu (Ehime U.)
report on behalf of the MAXI team:
The MAXI/GSC nova alert system triggered a bright uncatalogued X-ray transient
source at  11:38:25 UT on 9 August 2018.
Assuming that the source flux was constant over the transit,
we obtain the source position at
(R.A., Dec) = (297.793 deg, -34.663 deg) = (19 51 10, -34 39 46) (J2000)
with a 90% C.L. statistical error of 0.09 deg and an additional systematic
uncertainty of 0.1 deg (90% containment radius).
The X-ray flux averaged over the scan was 890 +- 57 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) = (297.202, -33.964) deg = (19 48 48, -33 57 49) (J2000)
(R.A., Dec) = (297.086, -34.046) deg = (19 48 20, -34 02 46) (J2000)
(R.A., Dec) = (298.358, -35.535) deg = (19 53 25, -35 32 04) (J2000)
(R.A., Dec) = (298.475, -35.451) deg = (19 53 54, -35 27 03) (J2000)
There was no significant excess flux in the previous transit at UT 10:05
with an upper limit of 20 mCrab.