MAXI/GSC detection of a bright X-ray flare from an eclipsing binary, Algol

ATel #3096; M. Sugizaki (RIKEN), H. Negoro (Nihon U.), A. Uzawa (Chuo U.), S. Ueno, H. Tomida, M. Kohama, M. Ishikawa (JAXA), T. Mihara, Y. E. Nakagawa, M. Serino, T. Yamamoto, T. Sootome, M. Matsuoka (RIKEN), N. Kawai, M. Morii, K. Sugimori, R. Usui (Tokyo Tech), A. Yoshida, K. Yamaoka, S. Nakahira (AGU), H. Tsunemi, M. Kimura, H. Kitayama (Osaka U.), M. Nakajima, H. Ozawa, F. Suwa (Nihon U.), Y. Ueda, N. Isobe, S. Eguchi, K. Hiroi, M. Shidatsu (Kyoto U.), A. Daikyuji (Miyazaki U.), Y. Tsuboi, T. Matsumura, K. Yamazaki report on behalf of the MAXI team
on 31 Dec 2010; 18:03 UT
Credential Certification: Mutsumi Sugizaki (sugizaki@riken.jp)

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On 2010-12-30 23:50 (UT) (MJD=55560.97), MAXI/GSC transient-alert system detected a flaring event from the position consistent with Algol (Beta Persei). The source flux in 2-20 keV band had been below 10 mCrab until the previous MAXI/GSC scan transit at 22:19 (UT) (MJD=55560.91). It was then found to be 101+-14 mCrab in the scan transit at 23:50 (UT). It is at the level of brightest X-ray flares from this source. Following this, the flux decays in a time scale of a few hours. The change of the fluxes in the 2-4 and 4-10 keV bands suggests that the spectrum might be softened during the flare. The observed fluxes in the 2-20 keV band at each scan transit were

 
MJD       flux and 1-sigma statistical error. 
55560.91  8   +- 8  (mCrab) 
55560.97  101 +- 14 
55561.03  88  +- 14 
55561.09  28  +- 9 
55561.16  5   +- 8 
55561.22  11  +- 8 
55561.28  10  +- 7 

The latest MAXI/GSC light curve and image of the source are available at the following URL:
http://maxi.riken.jp/top/index.php?cid=1&jname=J0308+409