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GCN Circular 33265

Subject
GRB 230204B: MAXI/GSC detection
Date
2023-02-04T22:51:17Z (a year ago)
From
Motoko Serino at Aoyama Gakuin U. <serino@phys.aoyama.ac.jp>
M. Serino (AGU), W. Iwakiri (Chiba U.),
H. Negoro, M. Nakajima, K. Kobayashi, M. Tanaka, Y. Soejima (Nihon U.),
T. Mihara, T. Kawamuro, S. Yamada, T. Tamagawa, M. Matsuoka (RIKEN),
T. Sakamoto, S. Sugita, H. Hiramatsu, H. Nishikawa, A. Yoshida (AGU),
Y. Tsuboi, J. Kohara, S. Urabe, S. Nawa, N. Nemoto (Chuo U.),
M. Shidatsu, M. Iwasaki (Ehime U.),
N. Kawai, M. Niwano, R. Hosokawa, Y. Imai, N. Ito, Y. Takamatsu (Tokyo Tech),
S. Nakahira, S. Ueno, H. Tomida, M. Ishikawa, T. Kurihara (JAXA),
Y. Ueda, S. Ogawa, K. Setoguchi, T. Yoshitake, K. Inaba, Y. Nakatani (Kyoto U.),
M. Yamauchi, T. Sato, R. Hatsuda, R. Fukuoka, Y. Hagiwara, Y. Umeki (Miyazaki U.),
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 21:47:51 UT on 4 Feb 2023.
Assuming that the source flux was constant over the transit,
we obtain the source position at
(R.A., Dec) = (197.581 deg, -21.752 deg) = (13 10 19, -21 45 07) (J2000)
with a statistical 90% C.L. elliptical error region
with long and short radii of 0.12 deg and 0.1 deg, respectively.
The roll angle of long axis from the north direction is 156.0 deg counterclockwise.
Without assumptions on the source constancy, we obtain a rectangular error box 
for the transient source with the following corners.
(196.900, -21.911) deg = (13 07 36, -21 54 39) (J2000)
(196.998, -22.143) deg = (13 07 59, -22 08 34) (J2000)
(198.373, -21.637) deg = (13 13 29, -21 38 13) (J2000)
(198.273, -21.406) deg = (13 13 05, -21 24 21) (J2000)
There is an additional systematic uncertainty of 0.1 deg (90% containment radius).
The X-ray flux averaged over the scan was 628 +- 49 mCrab
(4.0-10.0keV, 1 sigma error).
There was no significant excess flux in the previous transit at 20:15 UT
with an upper limit of 20 mCrab.
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