MAXI/GSC detection of a new bright X-ray flare from the dMe star AU Mic

ATel #15139; J. Kohara, W. Iwakiri, Y. Okamoto, S. Nawa, N. Nemoto, Y. Tsuboi, H. Kawai, S. Kitakoga (Chuo U.), 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), 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, T. Kurihara (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:
on 24 Dec 2021; 15:01 UT
Credential Certification: Wataru Iwakiri (wataru.iwakiri@riken.jp)

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The MAXI/GSC nova alert system triggered on the bright X-ray flare from the position consistent with the dMe type star AU Mic during a scan transit at 22:49 UT on Dec 15 2021. The estimated X-ray flux in the 2-20 keV band of this flare during this scan transit is about 9.0 (-1.6,+1.7) × 10^-9 erg/cm²/s. Assuming a distance of 9.7 pc (GaiaCollaboration et al. 2020), the peak luminosity is about 1 × 10³²erg/s. This is about three times brighter than the peak luminosity of the flare previously detected by MAXI on April 15, 2020(ATel #13635) and the largest ever observed by MAXI from AU Mic. In the next scan transit 00:22 UT on Dec 16 data of MAXI, the X-ray flare is still marginally detected with a significance of 3 sigma. If we assume that the flare flux decayed exponentially with time, the estimated e-folding time and the total energy in the 2 - 10 keV band of this flare are about 3000 sec and 3 × 10³⁵erg, respectively.