GCN Circular 22880

MAXI/GSC detection of GRB 180701A/MAXI J2119-045

W. Maruyama, H. Negoro (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), M. Nakajima, A. Sakamaki (Nihon U.), S. Ueno, H. Tomida, 
M. Ishikawa, Y. Sugawara, N. Isobe, R. Shimomukai (JAXA), Y. Ueda, 
A. Tanimoto, T. Morita, S. Yamada (Kyoto U.), Y. Tsuboi, W. Iwakiri, 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.) 

MAXI/GSC detected an uncatalogued short X-ray transient event at 06:47 UT 
on 2018 July 1. Assuming that the source flux was constant over the transit,
we obtain the source position at
(R.A., Dec) = (319.919 deg, -4.500 deg) = (21 19 40, -04 30 00) (J2000) 
with a statistical 90% C.L. elliptical error region 
with long and short radii of 0.36 deg and 0.32 deg, respectively. 
The roll angle of the long axis from the north direction is 57.0 deg counterclockwise. 
There is an additional systematic uncertainty of 0.1 deg (90% containment radius).
The X-ray flux averaged over the scan was 74 +- 19 mCrab
(4.0-10.0keV, 1 sigma error).
There was no significant excess flux in the previous transit at 05:14 UT
and in the next transit at 08:20 UT with an upper limit of 20 mCrab for each.

Due to the poor statistics, we could not obtain any useful information on 
the energy spectrum of the source.
The burst duration actually observed was about 10 seconds, which was, however, 
a lower limit of the duration for the event occurring at the beginning or end 
of the scan window. Note that, in such case, the error region to the scan 
direction is larger than that of the steady-flux-source case described above.

The nature of the source is quite unknown, then we refer to the source as 
GRB 180701A and MAXI J2119-045.