GCN Circular 26638

S. Sugita, M. Serino (AGU),
H. Negoro, M. Nakajima, W. Maruyama, M. Aoki, K. Kobayashi, R. Takagi
(Nihon U.),
T. Mihara, C. Guo, Y. Zhou, T. Tamagawa, M. Matsuoka (RIKEN),
T. Sakamoto, H. Nishida, A. Yoshida (AGU),
Y. Tsuboi, W. Iwakiri, R. Sasaki, H. Kawai, T. Sato (Chuo U.),
M. Shidatsu (Ehime U.),
N. Kawai, M. Oeda, K. Shiraishi (Tokyo Tech),
S. Nakahira, Y. Sugawara, S. Ueno, H. Tomida, M. Ishikawa, R.
Shimomukai, M. Tominaga (JAXA),
Y. Ueda, A. Tanimoto, S. Yamada, S. Ogawa, K. Setoguchi, T. Yoshitake
(Kyoto U.),
H. Tsunemi, T. Yoneyama, K. Asakura, S. Ide (Osaka U.),
M. Yamauchi, S. Iwahori, Y. Kurihara, K. Kurogi, K. Miike (Miyazaki U.),
T. Kawamuro (NAOJ),
K. Yamaoka (Nagoya U.),
Y. Kawakubo (LSU),
M. Sugizaki (NAOC)
report on behalf of the MAXI team:

The MAXI/GSC nova alert system triggered a bright uncatalogued X-ray
transient source at 21:55:28 UT on 2020 January 05.
Assuming that the source flux was constant over the transit,
we obtain the source position at
(R.A., Dec) = (319.281 deg, -35.846 deg) = (21 17 07, -35 50 45) (J2000)
with a statistical 90% C.L. elliptical error region
with long and short radii of 0.11 deg and 0.1 deg, respectively.
The roll angle of long axis from the north direction is 27.0 deg
counterclockwise.
There is an additional systematic uncertainty of 0.1 deg (90%
containment radius).

Without assumptions on the source constancy, we obtain a rectangular error
box for the transient source with the following corners:
(318.473, -35.441) deg = (21 13 53, -35 26 27) (J2000)
(318.374, -35.646) deg = (21 13 29, -35 38 45) (J2000)
(320.376, -36.262) deg = (21 21 30, -36 15 43) (J2000)
(320.470, -36.054) deg = (21 21 52, -36 03 14) (J2000)

The X-ray flux averaged over the scan was 710 +- 50 mCrab
(4.0-10.0keV, 1 sigma error).

There was no significant excess flux in the previous transit at 20:42 UT
with an upper limit of 20 mCrab.