GCN Circular 23005

R. Shimomukai (JAXA), H. Negoro (Nihon U.), W. Iwakiri (Chuo U.), 
M. Nakajima, W. Maruyama, A. Sakamaki (Nihon U.), 
T. Mihara, S. Nakahira, F. Yatabe, Y. Takao, M. Matsuoka (RIKEN), 
N. Kawai, M. Sugizaki, Y. Tachibana, K. Morita (Tokyo Tech), 
T. Sakamoto, M. Serino, S. Sugita, Y. Kawakubo, T. Hashimoto, A. Yoshida (AGU), 
S. Ueno, H. Tomida, M. Ishikawa, Y. Sugawara, N. Isobe (JAXA), 
Y. Ueda, A. Tanimoto, T. Morita, S. Yamada (Kyoto U.), Y. Tsuboi, R. Sasaki, 
H. Kawai, T. Sato (Chuo U.), H. Tsunemi, T. Yoneyama (Osaka U.), 
M. Yamauchi, K. Hidaka, S. Iwahori (Miyazaki U.), T. Kawamuro (NAOJ), 
K. Yamaoka (Nagoya U.), M. Shidatsu (Ehime U.) 
report on behalf of the MAXI team:

The MAXI/GSC nova alert system triggered on a bright uncatalogued X-ray 
transient source at 05:59:06 UT on 2018 July 22.
Assuming that the source flux was constant over the transit,
we obtain the source position at
(R.A., Dec) = (302.894 deg, 24.221 deg) = (20 11 34, +24 13 15) (J2000) 
with a statistical 90% C.L. elliptical error region 
with long and short radii of 0.21 deg and 0.17 deg, respectively. 
The roll angle of the long axis from the north direction is 14.0 deg counterclockwise. 
There is an additional systematic uncertainty of 0.1 deg (90% containment radius).

We estimated a rectangular error box for the transient source with the following corners:
(301.985, 24.469) deg = (20 07 56, +24 28 07) (J2000)
(301.898, 24.157) deg = (20 07 35, +24 09 26) (J2000)
(303.593, 23.939) deg = (20 14 22, +23 56 18) (J2000)
(303.685, 24.249) deg = (20 14 44, +24 14 56) (J2000)

The X-ray flux averaged over the scan was 259 +- 32 mCrab
(4.0-10.0keV, 1 sigma error).

There was no significant excess flux in the previous transit at UT 04:26.