GCN Circular 13731

M. Morii (Tokyo Tech), K. Yamaoka (Waseda U.), H. Negoro (Nihon U.),
S. Ueno, H. Tomida, S. Nakahira, M. Ishikawa (JAXA),
T. Mihara, M. Sugizaki, M. Serino, T. Yamamoto, J. Sugimoto, M. Matsuoka (RIKEN), 
N. Kawai, R. Usui, K. Ishikawa, T. Yoshii (Tokyo Tech),
A. Yoshida (AGU), H. Tsunemi, M. Kimura (Osaka U.),
M. Nakajima, M. Asada, N. Serita (Nihon U.),
Y. Ueda, K. Hiroi, M. Shidatsu, R. Sato (Kyoto U.),
Y. Tsuboi, M. Higa (Chuo U.),
M. Yamauchi, Y. Nishimura, T. Hanayama, K. Yoshidome (Miyazaki U.), 
report on behalf of the MAXI team:

MAXI/GSC triggered a bright uncatalogued X-ray transient source at UT 2012-09-08T22:35:13.
Assuming that the source flux was constant over the transit,
we obtain the source position at 

(R.A., Dec) = (230.64 deg, -25.79 deg) = (15 22 32, -25 47 42) (J2000)

with a statistical 90% C.L. elliptical error region
with long and short radii of 0.46 deg and 0.31 deg, respectively.
The position angle of long axis is -30 deg.
There is an additional systematic uncertainty of 0.1 deg (90% containment radius).

The preliminary flux of the transient source was 78 +- 19 mCrab (4 - 10 keV).
There was no significant detection at the transit location in the
previous and the next orbit (92 min before and after the detection)
with an upper limit of 20 mCrab.
There is no known bright X-ray source at the detected position.

Follow-up observations are encouraged.