GCN Circular 16855

H. Negoro (Nihon U.), S. Ueno, H. Tomida, S. Nakahira, M. Kimura, M. Ishikawa, Y. E. Nakagawa (JAXA), 
T. Mihara, M. Sugizaki, M. Morii, M. Serino, J. Sugimoto, T. Takagi, A. Yoshikawa, M. Matsuoka (RIKEN), 
N. Kawai, T. Yoshii, Y. Tachibana (Tokyo Tech), 
A. Yoshida, T. Sakamoto, Y. Kawakubo, H. Ohtsuki (AGU), 
H. Tsunemi, D. Uchida (Osaka U.), 
M. Nakajima, K. Fukushima, T. Onodera, K. Suzuki, T. Namba, M. Fujita, F. Honda (Nihon U.), 
Y. Ueda, M. Shidatsu, T. Kawamuro, T. Hori (Kyoto U.), 
Y. Tsuboi, A. Kawagoe (Chuo U.), 
M. Yamauchi, Y. Morooka (Miyazaki U.), 
K. Yamaoka (Nagoya U.) ,
report on behalf of the MAXI team:

A bright uncatalogued X-ray transient source was detected with MAXI/GSC 
at UT 2014-09-30T14:26. Assuming that the source flux was constant over 
the transit, we obtain the source position at

(R.A., Dec) = (344.875 deg, 52.428 deg) = (22 59 30, +52 25 40) (J2000), 
equivalently (l, b) = (106.186 deg, -6.766 deg), 

with a 90% C.L. statistical error of 0.40 deg and an additional systematic 
uncertainty of 0.1 deg (90% containment radius).
The X-ray flux averaged over the scan was 136 +- 30 mCrab (4-10 keV, 
1 sigma error). There was no significant excess flux in the previous transit 
at UT 2014-09-30T12:54.

The nature of the source is quite unknown. Since the source is located 
near the Galactic plane (l ~ -6.8 deg), this event might be an X-ray burst 
from a low mass X-ray binary near the Galactic plane. We tentatively name 
the source GRB 140930A and MAXI J2259+524 (originally, MAXI J2256+527
in the MAXI ML. "New-transient: 115").