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TITLE:   GCN CIRCULAR
NUMBER:  28726
SUBJECT: GRB 201021B MAXI/GSC detection
DATE:    20/10/21 18:31:15 GMT
FROM:    Satoshi Nakahira at RIKEN  <nakahira@crab.riken.jp>

S. Nakahira (JAXA), M. Serino (AGU), Y. Kawakubo (LSU),
H. Negoro, M. Nakajima, M. Aoki, K. Kobayashi, R. Takagi, K, Asakura, K, Seino (Nihon U.), 
T. Mihara, C. Guo, Y. Zhou, 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 (Tokyo Tech), 
Y. Sugawara, S. Ueno, H. Tomida, M. Ishikawa, M. Tominaga, T. Nagatsuka (JAXA), 
Y. Ueda, S. Yamada, S. Ogawa, K. Setoguchi, T. Yoshitake, U. Goto, R. Uematsu (Kyoto U.), 
H. Tsunemi (Osaka U.), 
M. Yamauchi, K. Kurogi, K. Miike (Miyazaki U.), 
T. Kawamuro (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 2020-10-21T16:18:55UT .
Assuming that the source flux was constant over the transit,
we obtain the source position at
(R.A., Dec) = (3.592 deg, -63.535 deg) = (00 14 22, -63 32 05) (J2000)
with a 90% C.L. statistical error of 0.24 deg and an additional systematic uncertainty of 0.1 deg (90% containment radius).
The X-ray flux averaged over the scan was 212 +- 25 mCrab (4.0-10.0keV, 1 sigma error).
There was no significant excess flux in the previous transit at UT 14:46 
and in the next transit at 17:51 UT with an upper limit of 20 mCrab for each.