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MAXI/GSC detects an X-ray brightening of Mrk 421

ATel #3637; K. Hiroi (Kyoto U.), M. Kohama, N. Isobe (JAXA), H. Negoro (Nihon U.), N. Kawai (Tokyo Tech) T. Mihara, M. Sugizaki, M. Serino, S. Nakahira, T. Yamamoto, T. Sootome, M. Matsuoka (RIKEN), S. Ueno, H. Tomida, M. Ishikawa (JAXA), M. Morii, Sugimori, R. Usui, T. Toizumi (Tokyo Tech), A. Yoshida, K. Yamaoka (AGU), H. Tsunemi, M. Kimura, H. Kitayama (Osaka U.), M. Nakajima, F. Suwa, M. Asada, H. Sakakibara (Nihon U.), Y. Ueda, M. Shidatsu (Kyoto U.), Y. Tsuboi, T. Matsumura, K. Yamazaki (Chuo U.) report on behalf of the MAXI team
on 8 Sep 2011; 07:12 UT
Credential Certification: Kazuo Hiroi (hiroi@kusastro.kyoto-u.ac.jp)

Subjects: X-ray, Blazar

MAXI/GSC has detected an X-ray brightening of the BL Lac object Mrk 421. The brightening started on 2011 August 22 (MJD=55795) or earlier after a long, low flux period from 2010 November 14 (MJD=55514) to 2011 July 24 (MJD=55766), when the 4-10 keV one-day average fluxes are below ~30 mCrab. The 2-4 keV and 4-10 keV average fluxes on 2011 September 7 (MJD=55811) and 8 during MAXI scans are: 55811.00-55811.25 : 55+-19 mCrab (2-4 keV) and 42+-18 mCrab (4-10 keV) 55811.50-55811.75 : 80+-25 mCrab (2-4 keV) and 33+-19 mCrab (4-10 keV) 55812.00-55812.25 : 75+-24 mCrab (2-4 keV) and 75+-21 mCrab (4-10 keV) (Note: The fluxes during 55811.75-55812.0 are omitted because of the contamination from an X-class solar flare.) The relatively rapid increase of the X-ray flux is reminiscent of the large X-ray flare on 2010 February 16, which reached approximately 150 mCrab (Isobe et al. ATel #2444, and Isobe et al. 2010 PASJ 52, L55). Therefore, prompt multiwavelength observations of this source are encouraged. The MAXI light curve of the source is updated daily at the following URL: http://maxi.riken.jp/top/index.php?cid=1&jname=J1104+382 .