[vsnet-grb-info 27440] GRB 210222A: MAXI/GSC detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  29543
SUBJECT: GRB 210222A: MAXI/GSC detection
DATE:    21/02/22 20:18:01 GMT
FROM:    Motoko Serino at RIKEN/MAXI  <motoko at crab.riken.jp>

M. Nakajima (Nihon U.), M. Serino (AGU), Y. Kawakubo (LSU),
H. Negoro, M. Aoki, K. Kobayashi, R. Takagi, K. Asakura, K. Seino (Nihon U.),
T. Mihara, T. Tamagawa, M. Matsuoka (RIKEN),
T. Sakamoto, S. Sugita, H. Nishida, K. Komachi, A. Yoshida (AGU),
Y. Tsuboi, W. Iwakiri, R. Sasaki, H. Kawai, Y. Okamoto, S. Kitakoga (Chuo U.),
M. Shidatsu (Ehime U.),
N. Kawai, R. Adachi, M. Niwano, R. Hosokawa (Tokyo Tech),
S. Nakahira, Y. Sugawara, S. Ueno, H. Tomida, M. Ishikawa, M. Tominaga, T. Nagatsuka (JAXA),
Y. Ueda, S. Yamada, S. Ogawa, K. Setoguchi, T. Yoshitake, Y. Goto, R. Uematsu (Kyoto U.),
H. Tsunemi (Osaka U.),
M. Yamauchi, K. Kurogi, K. Miike (Miyazaki U.),
T. Kawamuro (UDP/NAOJ),
K. Yamaoka (Nagoya U.),
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 2021-02-22T15:59:19 UT.
Assuming that the source flux was constant over the transit,
we obtain the source position at
(R.A., Dec) = (353.129 deg, -29.464 deg) = (23 32 30, -29 27 50) (J2000)
with a statistical 90% C.L. elliptical error region
with long and short radii of 0.11 deg and 0.04 deg, respectively.
The roll angle of long axis from the north direction is 90.0 deg counterclockwise.
There is an additional systematic uncertainty of 0.1 deg (90% containment radius).
The X-ray flux averaged over the scan was 389 +- 38 mCrab
(4.0-10.0keV, 1 sigma error).
There was no significant excess flux in the previous transit at 14:26 UT
with an upper limit of 20 mCrab.