TITLE:   GCN CIRCULAR
NUMBER:  44746
SUBJECT: GRB 260531A: MAXI/GSC detection
DATE:    26/05/31 09:28:53 GMT
FROM:    Motoko Serino at Aoyama Gakuin U. <serino@phys.aoyama.ac.jp>

H. Aoe (Ehime U.), H. Negoro (Nihon U.), M. Serino, S. Sugita (AGU),
M. Nakajima, K. Saito, T. Yokoyama, M. Wada (Nihon U.),
T. Mihara, T. Tamagawa, N. Kawai, M. Matsuoka (RIKEN),
T. Sakamoto, Y. Kawakubo, H. Hiramatsu, A. Yoshida (AGU),
Y. Tsuboi, Y. Ishihara, H. Ogaki (Chuo U.),
M. Shidatsu, C. Kang, M. Uenishi, T. Usuki, S. Yatsuzuka (Ehime U.),
I. Takahashi, Y. Yatsu (Science Tokyo),
S. Nakahira, S. Ueno, H. Tomida, M. Kurihara (JAXA),
Y. Ueda, K. Fujiwara, S. Kobayashi (Kyoto U.),
M. Yamauchi, M. Nishio, C. Hiraizumi (Miyazaki U.),
K. Yamaoka (Nagoya U.),
M. Sugizaki (Kanazawa U.),
W. Iwakiri (Chiba U.),
T. Kawamuro (Osaka U.),
S. Yamada (Tohoku U),
S. Ogawa (TUS) 
report on behalf of the MAXI team:
The MAXI/GSC nova alert system triggered a bright uncatalogued X-ray transient source 
at 05:30:18 UT on 2026 May 31.
Assuming that the source flux was constant over the transit,
we obtain the source position at
(R.A., Dec) = (69.904 deg, -10.627 deg) = (04 39 36, -10 37 37) (J2000)
with a statistical 90% C.L. elliptical error region
with long and short radii of 0.23 deg and 0.17 deg, respectively.
The roll angle of long axis from the north direction is 64.0 deg counterclockwise.
There is an additional systematic uncertainty of 0.1 deg (90% containment radius).
The X-ray flux averaged over the scan was 230 +- 36 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) = (69.234, -11.160) deg = (04 36 56, -11 09 36) (J2000)
(R.A., Dec) = (69.533, -11.386) deg = (04 38 07, -11 23 09) (J2000)
(R.A., Dec) = (70.598, -10.018) deg = (04 42 23, -10 01 04) (J2000)
(R.A., Dec) = (70.300, -9.794) deg = (04 41 11, -09 47 38) (J2000)
There was no significant excess flux in the previous transit at 03:57 UT
and in the next transit at 07:03 UT with an upper limit of 20 mCrab for each.

Note that this position is consistent with the position of Seyfert Galaxy MCG-02-12-050,
but it is not clear if this transient is related to MCG-02-12-050 at this time.