TITLE: GCN CIRCULAR NUMBER: 41602 SUBJECT: GRB 250830B: MAXI/GSC detection DATE: 25/08/30 05:37:22 GMT FROM: Hitoshi Negoro at Nihon University/MAXI team <negoro.hitoshi@nihon-u.ac.jp> T. Usuki (Ehime U.), H. Negoro, M. Nakajima, K. Takagi, H. Takahashi, H. Nishio (Nihon U.), T. Mihara, T. Tamagawa, N. Kawai, M. Matsuoka (RIKEN), T. Sakamoto, M. Serino, 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 (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.), S. Yamada (Tohoku U),report on behalf of the MAXI team: The MAXI/GSC nova alert system triggered on a bright uncatalogued X-ray transient source at 03:56:44 UT on August 30, 2025. Assuming that the source flux was constant over the transit, we obtain the source position at (R.A., Dec) = (105.209 deg, -64.628 deg) = (07 00 50, -64 37 40) (J2000) with a 90% C.L. statistical error of 0.33 deg and an additional systematic uncertainty of 0.1 deg (90% containment radius). The X-ray flux averaged over the scan was 225 +- 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) = (105.751, -63.592) deg = (07 03 00, -63 35 31) (J2000) (R.A., Dec) = (104.300, -63.666) deg = (06 57 11, -63 39 57) (J2000) (R.A., Dec) = (104.713, -65.344) deg = (06 58 51, -65 20 38) (J2000) (R.A., Dec) = (106.255, -65.266) deg = (07 05 01, -65 15 57) (J2000) There was no significant excess flux in the previous transit at 02:23 UT and in the next transit at 05:30 UT with an upper limit of 20 mCrab for each. We requested Swift/XRT followup observation. View this GCN Circular online at https://gcn.nasa.gov/circulars/41602. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...