GCN Circular 13282

N. Serita, H. Negoro, M. Nakajima, M. Asada, H. Sakakibara (Nihon U.), 
M. Serino, T. Mihara, M. Sugizaki, T. Yamamoto, M. Matsuoka (RIKEN), 
S. Nakahira, S. Ueno, H. Tomida, M. Ishikawa (JAXA),
N. Kawai, M. Morii, R. Usui, K. Ishikawa (Tokyo Tech),
A. Yoshida (AGU),
H. Tsunemi, M. Kimura (Osaka 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.), 
K. Yamaoka (Waseda U.)
report on behalf of the MAXI team:

During a scan transit centered at UT 2012-05-10T08:47:44,
MAXI/GSC detected a short X-ray transient lasting about 27 seconds 
within the 42 seconds triangular transit response of MAXI/GSC.
Judging from its hardness ratio, 
this transient is probably a gamma-ray burst.

Assuming that the source flux was constant over the transit, 
we obtain the source position at

(R.A., Dec) = (+44.285 deg, +72.850deg) = ( 02 57 08.60, +72 51 00.8 )(J2000)

which has a statistical uncertainty of 10 arcmin at the 90% confidence limit 
and an additional systematic uncertainty of 6 arcmin (90% containment radius).
Due to a short burst duration, the uncertainty for the scan direction is possibly larger than this estimation.
Without assuming a constant flux of the source,
a rectangular sky region of 90% confidence
is 0.4 degrees by 1.4 degrees with the following corners:

(R.A., Dec) = (+41.76 deg, +72.60 deg) = (02 47  2, +72 36 12)(J2000)
(R.A., Dec) = (+41.77 deg, +73.02 deg) = (02 47  4, +73 01 20)(J2000)
(R.A., Dec) = (+46.50 deg, +72.97 deg) = (03 06  0, +72 58  4)(J2000)
(R.A., Dec) = (+46.40 deg, +72.55 deg) = (03 05 36, +72 32 59)(J2000).

The preliminary flux estimate (4-10 keV) of the source was 330+-40 mCrab.

There was no significant detection at the transit location in the
previous and the following orbits (92 min before and after the detection) 
with an upper limit of 20 mCrab.

Follow-up observations are encouraged.