TITLE:   GCN CIRCULAR
NUMBER:  37124
SUBJECT: GRB 240809B: MAXI/GSC detection
DATE:    24/08/10 02:42:17 GMT
FROM:    Wataru Iwakiri at Chiba University <iwakiri.wataru.buz@gmail.com>

M. Kurihara (JAXA), M. Nakajima, H. Negoro (Nihon U.), W. Iwakiri (Chiba U.),
Y. Kudo, H. Shibui, K. Takagi, H. Takahashi, K. Tatano, H. Nishio (Nihon U.),
T. Mihara, T. Kawamuro, S. Yamada, S. Wang, T. Tamagawa, N. Kawai, M. Matsuoka (RIKEN),
T. Sakamoto, M. Serino, S. Sugita, Y. Kawakubo, H. Hiramatsu, H. Nishikawa, Y. Kondo, A. Yoshida (AGU),
Y. Tsuboi, H. Sugai, N. Nagashima (Chuo U.),
M. Shidatsu, Y. Niida (Ehime U.),
I. Takahashi, M. Niwano, N. Higuchi, Y. Yatsu (Tokyo Tech),
S. Nakahira, S. Ueno, H. Tomida, M. Ishikawa, S. Ogawa (JAXA),
Y. Ueda, Y. Okada (Kyoto U.),
M. Yamauchi, Y. Otsuki, T. Hasegawa, M. Nishio (Miyazaki U.),
K. Yamaoka (Nagoya U.),
M. Sugizaki (Kanazawa U.),

The MAXI/GSC nova alert system triggered a bright uncatalogued X-ray transient source at 2024-08-09T19:36:59 UT.
Assuming that the source flux was constant over the transit,
we obtain the source position at
(R.A., Dec) = (238.792 deg, -21.308 deg) = (15 55 10, -21 18 28) (J2000)
with a statistical 90% C.L. elliptical error region
with long and short radii of 0.29 deg and 0.25 deg, respectively.
The roll angle of long axis from the north direction is 160.0 deg counterclockwise.
There is an additional systematic uncertainty of 0.1 deg (90% containment radius).
The X-ray flux averaged over the scan was 90 +- 20 mCrab
(4.0-10.0keV, 1 sigma error).
There was no significant excess flux in the previous transit at 18:40 UT
and in the next transit at 2024-08-10 01:48 UT with an upper limit of 20 mCrab for each.