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MAXI/GSC detection of a bright X-ray flare from Mrk 421

ATel #5320; S. Ueno (JAXA), H. Negoro (Nihon U), T. Mihara, M. Sugizaki, M. Serino, M. Morii, T. Yamamoto, J. Sugimoto, T. Takagi, M. Matsuoka (RIKEN), H. Tomida, S. Nakahira, M. Kimura, M. Ishikawa, Y. Nakagawa (JAXA), N. Kawai, R. Usui, K. Ishikawa, T. Yoshii (Tokyo Tech), A. Yoshida, T. Sakamoto, Y. Nakano, Y. Kawakubo (AGU), H. Tsunemi, M. Sasaki (Osaka U.), M. Nakajima, K. Fukushima, T. Onodera, K. Suzuki (Nihon U.), Y. Ueda, M. Shidatsu, T. Kawamuro (Kyoto U.), Y. Tsuboi, M. Higa (Chuo U.), M. Yamauchi, K. Yoshidome, H. Yamada, Y. Ogawa (Miyazaki U.), K. Yamaoka (Nagoya U.) report on behalf of the MAXI team
on 24 Aug 2013; 04:57 UT
Credential Certification: Shiro Ueno (ueno.shiro@jaxa.jp)

Subjects: X-ray, AGN, Blazar

MAXI/GSC has detected an X-ray brightening of the BL Lac object Mrk 421. The brightening started around 2013 August 14 (MJD=56518).

The MAXI daily fluxes for the last month are:
2013 Jul 15 (MJD 56488): 21 +- 6 mCrab (2-4 keV) and < 26 mCrab (4-10 keV);
2013 Aug 13 (MJD 56517): 18 +- 7 mCrab (2-4 keV) and < 24 mCrab (4-10 keV);
2013 Aug 14 (MJD 56518): 43 +- 6 mCrab (2-4 keV) and 23 +- 10 mCrab (4-10 keV);
2013 Aug 15 (MJD 56519): 56 +- 6 mCrab (2-4 keV) and 19 +- 10 mCrab (4-10 keV);
2013 Aug 16 (MJD 56520): 46 +- 5 mCrab (2-4 keV) and 31 +- 10 mCrab (4-10 keV);
2013 Aug 17 (MJD 56521): 48 +- 5 mCrab (2-4 keV) and 31 +- 9 mCrab (4-10 keV);
2013 Aug 18 (MJD 56522): 59 +- 5 mCrab (2-4 keV) and 38 +- 9 mCrab (4-10 keV);
2013 Aug 19 (MJD 56523): 72 +- 5 mCrab (2-4 keV) and 49 +- 9 mCrab (4-10 keV);
2013 Aug 20 (MJD 56524): 92 +- 5 mCrab (2-4 keV) and 70 +- 9 mCrab (4-10 keV);
2013 Aug 21 (MJD 56525): 60 +- 5 mCrab (2-4 keV) and 31 +- 9 mCrab (4-10 keV);
2013 Aug 22 (MJD 56526): 81 +- 7 mCrab (2-4 keV) and 58 +- 13 mCrab (4-10 keV);
2013 Aug 23 (MJD 56527): 85 +- 6 mCrab (2-4 keV) and 71 +- 10 mCrab (4-10 keV).
(Note: The data gap between 2013 July 16 and August 12 is due to temporal change in the MAXI sky coverage.)

The relatively rapid increase of the X-ray flux is reminiscent of the historically brightest 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 .

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