TITLE:   GCN CIRCULAR
NUMBER:  33760
SUBJECT: GRB 230510B: MAXI/GSC detection
DATE:    23/05/10 23:29:07 GMT
FROM:    Satoshi Sugita at Aoyama Gakuin U. <sugita@phys.aoyama.ac.jp>

M. Nakajima (Nihon U.), Y. Kawakubo (LSU), S. Sugita, M. Serino (AGU),
H. Negoro, K. Kobayashi, M. Tanaka, Y. Soejima, Y. Kudo (Nihon U.),
T. Mihara, T. Kawamuro, S. Yamada, T. Tamagawa, N. Kawai, M. Matsuoka (RIKEN),
T. Sakamoto, H. Hiramatsu, H. Nishikawa, A. Yoshida (AGU),
Y. Tsuboi, S. Urabe, S. Nawa, N. Nemoto (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 (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  21:22:03 UT 10 May 2023.
Assuming that the source flux was constant over the transit,
we obtain the source position at
(R.A., Dec) = (0.692 deg, 27.541 deg) = (00 02 46, +27 32 27) (J2000)
with a statistical 90% C.L. elliptical error region
with long and short radii of 0.15 deg and 0.14 deg, respectively.
The roll angle of long axis from the north direction is 139.0 deg
counterclockwise.
Without assumptions on the source constancy, we obtain a rectangular error
box for the transient source with the following corners:
(R.A., Dec) = (0.127, 28.437) deg = (00 00 30, +28 26 13) (J2000)
(R.A., Dec) = (359.878, 28.290) deg = (23 59 30, +28 17 23) (J2000)
(R.A., Dec) = (0.966, 26.843) deg = (00 03 51, +26 50 34) (J2000)
(R.A., Dec) = (1.213, 26.988) deg = (00 04 51, +26 59 16) (J2000)
There is an additional systematic uncertainty of 0.1 deg (90%
containment radius).
The trigger time and position was consistent with that of GRB 230510B
(Fermi GBM, GCN 33759)
The X-ray flux averaged over the scan was 635 +- 75 mCrab
(4.0-10.0keV, 1 sigma error).
There was no significant excess flux in the previous transit at 19:49 UT
and in the next transit at 22:54 UT with an upper limit of 20 mCrab for each.