TITLE:   GCN CIRCULAR
NUMBER:  16242
SUBJECT: GRB 140509B: MAXI/GSC detection
DATE:    14/05/09 18:05:51 GMT
FROM:    Takanori Sakamoto at AGU  <tsakamoto@phys.aoyama.ac.jp>

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

The MAXI/GSC nova alert system triggered a bright uncatalogued X-ray transient source 
at 2014-05-09T16:18:38 UT.  Assuming that the source flux was constant over the transit,
we obtain the source position at

(R.A., Dec) = (312.966 deg, 21.016 deg) = (20 51 51, +21 00 57) (J2000)

with a statistical 90% C.L. elliptical error region with long and short radii of 0.27 deg and 
0.24 deg respectively.  The roll angle of long axis from the north direction is 124.0 deg 
counterclockwise.  Without the assumption about the source constancy, we obtain a rectangular 
error box for the transient source with the following corners:

(312.482 deg, 20.145 deg) = (20 49 55, +20 08 40) (J2000)
(312.039 deg, 20.483 deg) = (20 48 09, +20 28 59) (J2000)
(313.694 deg, 22.120 deg) = (20 54 46, +22 07 11) (J2000)
(314.137 deg, 21.776 deg) = (20 56 32, +21 46 32) (J2000)

There is an additional systematic uncertainty of 0.1 deg (90% containment radius).
The X-ray flux averaged over the scan was 98 +- 23 mCrab (4-10keV, 1 sigma error).
There was no significant excess flux in the previous transit at UT 14:45 with an upper 
limit of 20 mCrab.