TITLE:   GCN CIRCULAR
NUMBER:  35796
SUBJECT: GRB 240225B: MAXI/GSC detection
DATE:    24/02/26 03:37:58 GMT
FROM:    Yuta Kawakubo at Louisiana State University <kawakubo1@lsu.edu>

M. Nakajima, H. Negoro (Nihon U.), Y. Kawakubo (LSU),
K. Kobayashi, M. Tanaka, Y. Soejima, Y. Kudo (Nihon U.),
T. Mihara, T. Kawamuro, S. Yamada, S. Wang, T. Tamagawa, N. Kawai, M. Matsuoka (RIKEN),
T. Sakamoto, M. Serino, S. Sugita, H. Hiramatsu, H. Nishikawa, A. Yoshida (AGU),
Y. Tsuboi, S. Urabe, S. Nawa, N. Nemoto, E.Goto (Chuo U.),
M. Shidatsu (Ehime U.),
I. Takahashi, M. Niwano, S. Sato, N. Higuchi, Y. Yatsu (Tokyo Tech),
S. Nakahira, S. Ueno, H. Tomida, M. Ishikawa, S. Ogawa, T. Kurihara (JAXA),
Y. Ueda, K. Setoguchi, T. Yoshitake, Y. Nakatani, Y. Okada (Kyoto U.),
M. Yamauchi, Y. Hagiwara, Y. Umeki, Y. Otsuki (Miyazaki U.),
K. Yamaoka (Nagoya U.),
M. Sugizaki (NAOC),
W. Iwakiri (Chiba U.)
report on behalf of the MAXI team:

The MAXI/GSC nova alert system triggered a bright uncatalogued X-ray transient source  
at 20:15:46 UT on February 25, 2024.
Assuming that the source flux was constant over the transit,
we obtain the source position at
(R.A., Dec) = (128.458 deg, 27.487 deg) = (08 33 49, +27 29 13) (J2000)
with a statistical 90% C.L. elliptical error region
with long and short radii of 0.13 deg and 0.11 deg, respectively.
The roll angle of long axis from the north direction is 67.0 deg counterclockwise.
There is an additional systematic uncertainty of 0.1 deg (90% containment radius).
The X-ray flux averaged over the scan was 874 +- 86 mCrab
(4.0-10.0keV, 1 sigma error).
Without assumptions on the source constancy, we obtain a rectangular error
box for the transient source with the following corners:
(R.A., Dec) = (127.906, 26.756) deg = (08 31 37, +26 45 21) (J2000)
(R.A., Dec) = (128.157, 26.654) deg = (08 32 37, +26 39 14) (J2000)
(R.A., Dec) = (128.895, 28.075) deg = (08 35 34, +28 04 29) (J2000)
(R.A., Dec) = (128.642, 28.179) deg = (08 34 34, +28 10 44) (J2000)
There was no significant excess flux in the previous transit at 18:43 UT
and in the next transit at 21:48 UT with an upper limit of 20 mCrab for each.