GCN Circular 45592

GRB 260916A: MAXI/GSC detection

M. Uenishi (Ehime U.), M. Nakajima (Nihon U.), Y. Kawakubo (AGU), 
H. Negoro, K. Saito, T. Yokoyama, M. Wada (Nihon U.),
T. Mihara, T. Tamagawa, N. Kawai, M. Matsuoka (RIKEN),
T. Sakamoto, M. Serino, S. Sugita, H. Hiramatsu, A. Yoshida (AGU),
Y. Tsuboi, Y. Ishihara, H. Ogaki (Chuo U.),
M. Shidatsu, C. Kang, T. Usuki, S. Yatsuzuka, H. Aoe (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 08:51:44 UT on 16 September 2026.
Assuming that the source flux was constant over the transit,
we obtain the source position at
(R.A., Dec) = (17.811 deg, -26.193 deg) = (01 11 14, -26 11 34) (J2000)
with a statistical 90% C.L. elliptical error region
with long and short radii of 0.19 deg and 0.18 deg, respectively.
The roll angle of long axis from the north direction is 42.0 deg counterclockwise.
There is an additional systematic uncertainty of 0.1 deg (90% containment radius).
The X-ray flux averaged over the scan was 165 +- 26 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:
(17.868, -25.913) deg = (01 11 28, -25 54 46) (J2000)
(17.539, -26.135) deg = (01 10 09, -26 08 06) (J2000)
(17.867, -26.526) deg = (01 11 28, -26 31 33) (J2000)
(18.196, -26.303) deg = (01 12 47, -26 18 10) (J2000)
There was no significant excess flux in the previous transit at 07:18 UT 
with an upper limit of 20 mCrab.