TITLE:   GCN CIRCULAR
NUMBER:  28363
SUBJECT: GRB 200903D: MAXI/GSC detection
DATE:    20/09/04 01:00:17 GMT
FROM:    Motoko Serino at RIKEN/MAXI  <motoko@crab.riken.jp>

S. Ogawa (Kyoto U.),
H. Negoro, M. Nakajima, M. Aoki, K. Kobayashi, R. Takagi, K, Asakura, K, Seino (Nihon U.),
T. Mihara, C. Guo, Y. Zhou, T. Tamagawa, M. Matsuoka (RIKEN),
T. Sakamoto, M. Serino, S. Sugita, H. Nishida, A. Yoshida (AGU),
Y. Tsuboi, W. Iwakiri, R. Sasaki, H. Kawai, Y. Okamoto, S. Kitakoga (Chuo U.),
M. Shidatsu (Ehime U.),
N. Kawai, R. Adachi, M. Niwano (Tokyo Tech),
S. Nakahira, Y. Sugawara, S. Ueno, H. Tomida, M. Ishikawa, M. Tominaga, T. Nagatsuka (JAXA),
Y. Ueda, S. Yamada, K. Setoguchi, T. Yoshitake (Kyoto U.),
H. Tsunemi (Osaka U.),
M. Yamauchi, K. Kurogi, K. Miike (Miyazaki U.),
T. Kawamuro (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 15:32:04 UT .
Assuming that the source flux was constant over the transit,
we obtain the source position at
(R.A., Dec) = (312.777 deg, -0.598 deg) = (20 51 06, -00 35 52) (J2000)
with a statistical 90% C.L. elliptical error region
with long and short radii of 0.26 deg and 0.22 deg, respectively.
The roll angle of long axis from the north direction is 55.0 deg counterclockwise.
There is an additional systematic uncertainty of 0.1 deg (90% containment radius).
The X-ray flux averaged over the scan was 182 +- 36 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:
There was no significant excess flux in the previous transit at UT 13:59
and in the next transit at 17:04 UT with an upper limit of 20 mCrab for each.