GCN Circular 21137

Y. Takao, M. Serino, S. Nakahira (RIKEN), S. Sugita (Tokyo Tech), H. Negoro (Nihon U.),
S. Ueno, H. Tomida, M. Ishikawa, Y. Sugawara, N. Isobe (JAXA),
T. Mihara, M. Sugizaki, W. Iwakiri, M. Shidatsu, M. Matsuoka (RIKEN),
N. Kawai, 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:

At 2017-05-11T06:00 UT, the MAXI/GSC detected an uncatalogued X-ray
transient source.
The position reported to the MAXI new-transient mailing list was not accurate
due to an error of attitude determination.
With the corrected attitude information, we update the source
position assuming a constant source flux over the scan transit to be

 (R.A., Dec) = (300.633 deg, 33.315 deg) = (20 02 31, +33 18 53) (J2000)

with a statistical 90% C.L. elliptical error region
with long and short radii of 0.29 deg and 0.25 deg, respectively.
The roll angle of long axis from the north direction is 170.0 deg counterclockwise.
There is an additional systematic uncertainty of 0.1 deg (90% containment radius).

The position and the time of the burst are consistent with a burst detected
by Fermi/GBM (trigger #516175156). Thus, we consider this event to be a GRB.
According to a quick-look light curve of Fermi/GBM, MAXI/GSC observed a tail 
part of the GRB.

The averaged X-ray flux was 228 +- 35 mCrab (4-10 keV). 
There were no significant excess fluxes at the previous
and followed scan transits at 2017/05/11 04:27 UT and 07:33 UT, 
respectively, with an upper limit of 20 mCrab for each.