TITLE:   GCN CIRCULAR
NUMBER:  42376
SUBJECT: GRB 250911A: MAXI/GSC detection
DATE:    25/10/22 05:22:50 GMT
FROM:    Hitoshi Negoro at Nihon University/MAXI team <negoro.hitoshi@nihon-u.ac.jp>

H. Negoro (Nihon U.), T. Mihara (RIKEN), M. Serino (AGU), M. Nakajima, K. Takagi,
H. Takahashi, H. Nishio (Nihon U.),  T. Tamagawa, N. Kawai, M. Matsuoka (RIKEN),
T. Sakamoto, S. Sugita, Y. Kawakubo, H. Hiramatsu, Y. Kondo, A. Yoshida (AGU),
Y. Tsuboi, H. Sugai, N. Nagashima, Y. Ishihara (Chuo U.), M. Shidatsu, C. Kang,
T. Nakamoto, M. Uenishi, T. Usuki, S. Yatsuzuka (Ehime U.),
I. Takahashi, Y. Yatsu (Science Tokyo), S. Nakahira, S. Ueno, H. Tomida, M. Ishikawa,
S. Ogawa, M. Kurihara (JAXA), Y. Ueda, K. Fujiwara (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.), and S. Yamada (Tohoku U),

We report on the detection of GRB 250911A by MAXI 
(Swift-BAT: GCN 41781, 41812, COLIBRI: GCN 41782, Swift-XRT: GCN 41783, 41784, 41804, 
Swift-UVOT: 41800, MASTER: GCN 41806, GECAM-B: GCN 41813, Insight-HXMT: GCN 41827, 
Konus-Wind: GCN 41939).

MAXI detected the burst for approximately 40 seconds, centered at around 01:29:46 on
September 11, 2025. The period coincides with the main peak of the burst detected by Swift,
HXMT, and Konus-Wind. The 4-10 keV X-ray flux averaged over the scan was 2041 ± 83 mCrab.

The MAXI light curve is shown at
https://maxi.riken.jp/grbs/250911a/

GRB 250911A was about 0.8 degrees away from the bright NS-LMXB GX 9+9. 
Due to the X-ray photon confusion from GX 9+9, we were unable to obtain firm upper 
limits or flux in the previous transit at 23:57 UT on September 10 and the next transit 
at 03:02 UT. 
Some software problem during the burst partly causes the late notice.