TITLE: GCN CIRCULAR NUMBER: 43580 SUBJECT: GRB 260131B: MAXI/GSC detection DATE: 26/01/31 08:53:31 GMT FROM: Motoko Serino at Aoyama Gakuin U. <serino@phys.aoyama.ac.jp> H. Sugai (Chuo U.), D. Iijima, M. Serino (AGU), H. Negoro, M. Nakajima, K. Takagi, H. Takahashi, H. Nishio (Nihon U.), T. Mihara, T. Tamagawa, N. Kawai, M. Matsuoka (RIKEN), T. Sakamoto, S. Sugita, Y. Kawakubo, H. Hiramatsu, Y. Kondo, A. Yoshida (AGU), Y. Tsuboi, 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, 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) The MAXI/GSC nova alert system triggered a bright uncatalogued X-ray transient source at 06:43:02 UT on January 31, 2026. Assuming that the source flux was constant over the transit, we obtain the source position at (R.A., Dec) = (24.348 deg, 34.351 deg) = (01 37 23, +34 21 03) (J2000) with a statistical 90% C.L. elliptical error region with long and short radii of 0.11 deg and 0.09 deg, respectively. The roll angle of long axis from the north direction is 26.0 deg counterclockwise. There is an additional systematic uncertainty of 0.1 deg (90% containment radius). The X-ray flux averaged over the scan was 801 +- 56 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) = (23.945, 34.685) deg = (01 35 46, +34 41 06) (J2000) (R.A., Dec) = (23.826, 34.499) deg = (01 35 18, +34 29 56) (J2000) (R.A., Dec) = (25.021, 33.970) deg = (01 40 05, +33 58 11) (J2000) (R.A., Dec) = (25.142, 34.154) deg = (01 40 34, +34 09 14) (J2000) There was no significant excess flux in the previous transit at 05:10 UT and in the next transit at 08:16 UT with an upper limit of 20 mCrab for each. View this GCN Circular online at https://gcn.nasa.gov/circulars/43580. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...