[vsnet-grb-info 8329] GRB 090831: MAXI GSC detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  9852
SUBJECT: GRB 090831: MAXI GSC detection
DATE:    09/08/31 19:22:52 GMT
FROM:    Nobuyuki Kawai at Tokyo Tech  <nkawai at hp.phys.titech.ac.jp>

M. Matsuoka (JAXA), S. Miyoshi, M. Nakajima, H. Negoro, R. Ishiwata (Nihon
Univ.), K. Kawasaki, S. Ueno, H. Tomida, M. Suzuki, M. Ishikawa (JAXA),
T. Mihara, M. Kohama, Y.E. Nakagawa, M. Sugizaki, T. Yamamoto (RIKEN), 
N. Kawai, M. Morii, K. Sugimori (Tokyo Tech), A. Yoshida, K. Yamaoka, 
S. Nakahira (Aoyama G. Univ.), H. Tsunemi, M. Kimura (Osaka Univ.), 
Y. Ueda, N. Isobe, S. Eguchi and K. Hiroi (Kyoto Univ.) report on behalf of
the MAXI team:

The Gas Slit Camera (GSC) of MAXI, the all-sky X-ray monitor on the ISS,
detected a bright X-ray source at the position consistent with GRB 090831
(Rau et al, GCN 9850) in the energy range of 2-30 keV.  
The nominal location of the source as measured by GSC is 

(R.A., Dec.) = (145.4 deg, +51.4 deg) = (09:41:36, +51:24:00) (J2000)

with an estimated systematic uncertainty of about 1 degree.

The source was detected for 60 seconds during the transit of GSC over 
the source starting approximately at 07:36:35 UT on 31 August 2009, 
very close to the Fermi GBM trigger time.
The X-ray flux at the peak of the transit was about 3 Crab.
There are significant time structure within the transit light curve, 
which would be simply triangular for a steady source.

The all-sky image and the transit light curve is shown at the MAXI web site
http://maxi.riken.jp/ in the "News" section.

MAXI is currently in the commissioning phase that runs for three months.
The systematic uncertainty in localization will be significantly improved
with the progress of the alignment calibration.