TITLE:   GCN CIRCULAR
NUMBER:  25262
SUBJECT: GRB 190804B: MAXI/GSC detection
DATE:    19/08/04 12:00:58 GMT
FROM:    Hitoshi Negoro at Nihon U  <negoro.hitoshi@nihon-u.ac.jp>

T. Sato (Chuo U.), H. Negoro, M. Nakajima, W. Maruyama, M. Aoki, 
K. Kobayashi (Nihon U.), T. Mihara, T. Tamagawa, M. Matsuoka (RIKEN), 
T. Sakamoto, M. Serino, S. Sugita, H. Nishida, A. Yoshida (AGU), 
Y. Tsuboi, W. Iwakiri, R. Sasaki, H. Kawai (Chuo U.),  M. Shidatsu (Ehime U.),
N. Kawai, M. Sugizaki, M. Oeda, K. Shiraishi (Tokyo Tech), S. Nakahira, Y. Sugawara, 
S. Ueno, H. Tomida, M. Ishikawa, N.Isobe, R. Shimomukai, M. Tominaga (JAXA), 
Y. Ueda, A. Tanimoto, S. Yamada, S. Ogawa, K. Setoguchi, T. Yoshitake (Kyoto U.), 
H. Tsunemi, T. Yoneyama, K. Asakura, S. Ide (Osaka U.), 
M. Yamauchi, S. Iwahori, Y. Kurihara, K. Kurogi, K. Miike (Miyazaki U.), 
T. Kawamuro (NAOJ), K. Yamaoka (Nagoya U.), Y. Kawakubo (LSU)
report on behalf of the MAXI team:

The MAXI/GSC nova alert system triggered on an uncatalogued X-ray transient source at 
07:58:15 UT on  2019 August 04.
Assuming that the source flux was constant over the transit,
we obtain the source position at
(R.A., Dec) = (239.895 deg, -44.773 deg) = (15 59 34, -44 46 22) (J2000) 
with a statistical 90% C.L. elliptical error region 
with long and short radii of 0.29 deg and 0.24 deg, respectively. 
The roll angle of the long axis from the north direction is 39.0 deg counterclockwise. 
There is an additional systematic uncertainty of 0.1 deg (90% containment radius).
The X-ray flux averaged over the scan was 118 +- 21 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) = (240.071, -43.705) deg = (16 00 17, -43 42 17) (J2000)
(R.A., Dec) = (239.431, -43.730) deg = (15 57 43, -43 43 47) (J2000)
(R.A., Dec) = (239.594, -45.994) deg = (15 58 22, -45 59 38) (J2000)
(R.A., Dec) = (240.259, -45.968) deg = (16 01 02, -45 58 04) (J2000)
There was no significant excess flux in the previous transit at 06:25 UT, 
and in the next transit at 09:30 UT with an upper limit of 20 mCrab for each.