[vsnet-grb-info 25318] GRB 200320B: MAXI/GSC detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  27418
SUBJECT: GRB 200320B: MAXI/GSC detection
DATE:    20/03/21 14:13:23 GMT
FROM:    Hitoshi Negoro at Nihon U  <negoro.hitoshi at nihon-u.ac.jp>

S. Yamada (Kyoto U.), 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, M. Serino, S. Sugita, 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, R. Adachi, M. Niwano (Tokyo Tech), 
S. Nakahira, Y. Sugawara, S. Ueno, H. Tomida, M. Ishikawa, R. Shimomukai, M. Tominaga (JAXA), 
Y. Ueda, A. Tanimoto, 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 on a bright uncatalogued X-ray transient source 
at 13:12:27 UT on 2020 March 20. Assuming that the source flux was constant over the transit,
we obtain the source position at
(R.A., Dec) = (125.923 deg, -75.733 deg) = (08 23 41, -75 43 58) (J2000) 
with a statistical 90% C.L. elliptical error region 
with long and short radii of 0.68 deg and 0.65 deg, respectively. 
The roll angle of the long axis from the north direction is 59.0 deg counterclockwise. 
There is an additional systematic uncertainty of 0.1 deg (90% containment radius).
The X-ray flux averaged over the scan was 65 +- 22 mCrab
(4.0-10.0keV, 1 sigma error).
Without the assumption on the source constancy, we obtain a rectangular error
box for the transient source with the following corners:
(R.A., Dec) = (129.795, -77.155) deg = (08 39 10, -77 09 18) (J2000)
(R.A., Dec) = (132.879, -76.048) deg = (08 51 30, -76 02 52) (J2000)
(R.A., Dec) = (123.641, -74.339) deg = (08 14 33, -74 20 20) (J2000)
(R.A., Dec) = (120.277, -75.319) deg = (08 01 06, -75 19 08) (J2000)

In the previous transit at 10:05 UT, a weak (30 +- 16 mCrab at 4-10 keV) enhancement 
was also recognized. There was no significant excess flux in the next transit 
at 14:45 UT with an upper limit of 20 mCrab.

Finally, we note that due to the poor statistics, we can not confirm that this event is a GRB.
Therefore, we also name the source MAXI J0823-757.