TITLE:   GCN CIRCULAR
NUMBER:  21858
SUBJECT: GRB 170911A: MAXI/GSC detection
DATE:    17/09/11 15:54:51 GMT
FROM:    H. Negoro at Nihon U.  <negoro@phys.cst.nihon-u.ac.jp>

Y. Takao (RIKEN), H. Negoro (Nihon U.),
S. Ueno, H. Tomida, M. Ishikawa, Y. Sugawara, N. Isobe, R. Shimomukai (JAXA),
T. Mihara, M. Sugizaki, S. Nakahira, W. Iwakiri, M. Shidatsu, M. Matsuoka (RIKEN), 
N. Kawai, S. Sugita, T. Yoshii, Y. Tachibana, S. Harita, Y. Muraki, K. Morita (Tokyo Tech), 
A. Yoshida, T. Sakamoto, M. Serino, 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, H. Kawai (Chuo U.), 
M. Yamauchi, C. Hanyu, K, Hidaka (Miyazaki U.), 
T. Kawamuro (NAOJ), and K. Yamaoka (Nagoya U.)


The MAXI/GSC nova alert system triggered a bright uncatalogued X-ray transient source 
at 06:24:21 UT on 2017 September 11.
Assuming that the source flux was constant over the transit,
we obtain the source position at
(R.A., Dec) = (72.100 deg, 30.914 deg) = (04 48 23, +30 54 50) (J2000) 
with a statistical 90% C.L. elliptical error region 
with long and short radii of 0.38 deg and 0.32 deg, respectively. 
The roll angle of long axis from the north direction is 8.0 deg counterclockwise. 
There is an additional systematic uncertainty of 0.1 deg (90% containment radius).
The X-ray flux averaged over the scan was 119 +- 24 mCrab
(4.0-10.0keV, 1 sigma error).
Without the constant flux assumption, we also obtained a rectangular error box 
for the transient source with the following corners:
(R.A., Dec) = (70.630, 31.515) deg = (04 42 31, +31 30 55) (J2000)
(R.A., Dec) = (70.464, 30.944) deg = (04 41 51, +30 56 38) (J2000)
(R.A., Dec) = (73.457, 30.459) deg = (04 53 49, +30 27 31) (J2000)
(R.A., Dec) = (73.640, 31.026) deg = (04 54 33, +31 01 34) (J2000)
There is an additional systematic uncertainty of 0.1 deg (90% containment radius).

There was no significant excess flux in the previous transit at 04:51
and in the next transit at 07:56 with an upper limit of 20 mCrab for each.

Fermi is likely to detected this burst (Trigger number: 526803867).