TITLE: GCN CIRCULAR NUMBER: 31303 SUBJECT: GRB 211225A/MAXI J0827-071: MAXI/GSC detection DATE: 21/12/25 05:14:45 GMT FROM: Hitoshi Negoro at Nihon U T. Kurihara (JAXA), H. Negoro, M. Nakajima, K. Kobayashi, K. Asakura, K. Seino (Nihon U.), T. Mihara, T. Tamagawa, J. Li, M. Matsuoka (RIKEN), T. Sakamoto, M. Serino, S. Sugita, K. Komachi, H. Hiramatsu, A. Yoshida (AGU), Y. Tsuboi, W. Iwakiri, H. Kawai, Y. Okamoto, S. Kitakoga (Chuo U.), M. Shidatsu, M. Iwasaki (Ehime U.), N. Kawai, M. Niwano, R. Hosokawa, Y. Imai, N. Ito, Y. Takamatsu (Tokyo Tech), S. Nakahira, S. Ueno, H. Tomida, M. Ishikawa, M. Tominaga, T. Nagatsuka (JAXA), Y. Ueda, S. Yamada, S. Ogawa, K. Setoguchi, T. Yoshitake, Y. Goto, R. Uematsu, K. Inaba (Kyoto U.), H. Tsunemi (Osaka U.), M. Yamauchi, Y. Nonaka, T. Sato, R. Hatsuda, R. Fukuoka (Miyazaki U.), T. Kawamuro (UDP/NAOJ), K. Yamaoka (Nagoya U.), Y. Kawakubo (LSU), M. Sugizaki (NAOC) report on behalf of the MAXI team: The MAXI/GSC nova alert system triggered on a bright uncatalogued X-ray transient source at 03:22:28 UT on 2021 December 25. Assuming that the source flux was constant over the transit, we obtain the source position at (R.A., Dec) = (126.923 deg, -7.182 deg) = (08 27 41, -07 10 55) (J2000) with a statistical 90% C.L. elliptical error region with long and short radii of 0.20 deg and 0.17 deg, respectively. The roll angle of long axis from the north direction is 40.0 deg counterclockwise. Without assumptions on the source constancy, we obtain a rectangular error box for the transient source with the following corners: (R.A., Dec) = (126.189, -7.957) deg = (08 24 45, -07 57 25) (J2000) (R.A., Dec) = (126.475, -8.145) deg = (08 25 53, -08 08 41) (J2000) (R.A., Dec) = (127.569, -6.507) deg = (08 30 16, -06 30 25) (J2000) (R.A., Dec) = (127.284, -6.319) deg = (08 29 08, -06 19 08) (J2000) The X-ray flux averaged over the scan was 203 +- 29 mCrab (4.0-10.0keV, 1 sigma error). There was no significant excess flux in the previous transit at 01:49 UT with an upper limit of 20 mCrab.