GCN Circular 19404

Y.Ono (Tokyo Tech), S. Ueno, H. Tomida, S. Nakahira, M. Ishikawa, Y. E. Nakagawa, Y. Sugawara (JAXA), 
T. Mihara, M. Sugizaki, M. Serino, W. Iwakiri, M. Shidatsu, J. Sugimoto, T. Takagi, M. Matsuoka (RIKEN), 
N. Kawai, N.Isobe, S.Sugita, T. Yoshii, Y. Tachibana, T. Fujiwara (Tokyo Tech), 
A. Yoshida, T. Sakamoto, Y. Kawakubo, Y. Kitaoka (AGU), 
H. Tsunemi, R.Imatani (Osaka U.), 
H. Negoro, M. Nakajima, K. Tanaka, T. Masumitsu, T. Kawase (Nihon U.), 
Y. Ueda, T. Kawamuro, T. Hori, A. Tanimoto (Kyoto U.), 
Y. Tsuboi, Y. Nakamura, R. Sasaki (Chuo U.), 
M. Yamauchi, K. Furuya (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 UT 2016-05-09T09:04:16.

Assuming that the source flux was constant over the transit,
we obtain the source position at
(R.A., Dec) = (312.131 deg, 75.810 deg) = (20 48 31, +75 48 36) (J2000)
with a 90% C.L. statistical error of 0.06 deg and an additional systematic uncertainty of 0.1 deg (90% containment radius).
The X-ray flux averaged over the scan was 1307 +- 69 mCrab
(4-10keV, 1 sigma error).
Without assumptions on the source constancy,we obtain a rectangular error
box for the transient source with the following corners:
(310.897 deg, 75.728 deg) = (20 43 35, +75 43 40) (J2000)
(311.105 deg, 75.626 deg) = (20 44 25, +75 37 34) (J2000)
(313.379 deg, 75.887 deg) = (20 53 30, +75 53 14) (J2000)
(313.181 deg, 75.991 deg) = (20 52 43, +75 59 27) (J2000)

There was no significant excess flux in the previous transit at UT 2016-0509T07:32
with an upper limit of 20 mCrab.