GCN Circular 21243

M. Shidatsu, S. Motoko (RIKEN), H. Negoro (Nihon U.), 
S. Ueno, H. Tomida, M. Ishikawa, Y. Sugawara, N. Isobe (JAXA),
T. Mihara, M. Sugizaki, S. Nakahira, W. Iwakiri, M. Matsuoka (RIKEN), 
N. Kawai, S. Sugita, T. Yoshii, Y. Tachibana, S. Harita, Y. Muraki, K. Morita (Tokyo Tech), 
A. Yoshida, T. Sakamoto, Y. Kawakubo, Y. Kitaoka, T. Hashimoto (AGU), 
H. Tsunemi, T. Yoneyama (Osaka U.), 
M. Nakajima, T. Kawase, A. Sakamaki (Nihon U.),
Y. Ueda, T. Hori, A. Tanimoto, S. Oda (Kyoto U.), 
Y. Tsuboi, Y. Nakamura, R. Sasaki (Chuo U.), 
M. Yamauchi, C. Hanyu, K, Hidaka (Miyazaki U.), 
T. Kawamuro (NAOJ), 
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 20:42:58 UT on 2017 June 10. 
Assuming that the source flux was constant over the transit,
we obtain the source position at
(R.A., Dec) = (92.567 deg, -9.420 deg) = (06 10 16, -09 25 11) (J2000)
with a statistical 90% C.L. elliptical error region
with long and short radii of 0.24 deg and 0.2 deg, respectively.
The roll angle of long axis from the north direction is 123.0 deg counterclockwise. 
We estimated a rectangular error box for the transient source with the following corners:
(91.851, -10.701) deg = (06 07 24, -10 42 03) (J2000)
(91.421, -10.332) deg = (06 05 40, -10 19 54) (J2000)
(92.681, -8.737) deg = (06 10 43, -08 44 13) (J2000)
(93.111, -9.105) deg = (06 12 26, -09 06 16) (J2000).
There is an additional systematic uncertainty of 0.1 deg (90% containment radius).

The X-ray flux averaged over the scan was 127 +- 23 mCrab
(4.0-10.0keV, 1 sigma error).
There was no significant excess flux in the previous transit at UT 19:10
and in the next transit at UT 22:15 with an upper limit of 20 mCrab for each.