MAXI observation of a bright X-ray flare with multiple peaks from Mrk 421
ATel #4978; H. Negoro, K. Suzuki (Nihon U.), N. Kawai (Tokyo Tech), M. Serino (RIKEN), S. Ueno, H. Tomida, S. Nakahira, M. Kimura, M. Ishikawa (JAXA), T. Mihara, M. Sugizaki, M. Morii, T. Yamamoto, J. Sugimoto, T. Takagi, M. Matsuoka (RIKEN), R. Usui, K. Ishikawa, T. Yoshii (Tokyo Tech), A. Yoshida, T. Sakamoto, Y. Nakano (AGU), H. Tsunemi, M. Sasaki (Osaka U.), M. Nakajima, K. Fukushima, T. Onodera, (Nihon U.), Y. Ueda, M. Shidatsu, T. Kawamuro (Kyoto U.), Y. Tsuboi, M. Higa (Chuo U.), M. Yamauchi, K. Yoshidome, Y. Ogawa, H. Yamada (Miyazaki U.), K. Yamaoka (Nagoya U.) report on behalf of the MAXI team
on 15 Apr 2013; 02:32 UT
Credential Certification: Hitoshi Negoro (email@example.com)
Subjects: X-ray, AGN, Blazar
As reported from observations by NuSTAR (Balokovic et al. ATel #4974),
MAGIC and VERITAS (Cortina et al. ATel #4976), and
Fermi-LAT and Swift-XRT (Paneque et al. ATel #4977),
Mrk 421 recently exhibited an extremely bright flaring in X-rays
to the very high energy gamma-rays.
MAXI-GSC has also detected this bright flare (MAXI transient email
alert ID = 6394252311), and the 1-day averaged 2-10 keV flux observed
mostly doubled from ~37 mCrab on 2013 April 11 (UT) to
~85 mCrab on April 12 and ~75 mCrab on April 13. (Note that MAXI-GSC
observation temporally stopped from 01:47 to 10:57 on April 13
due to the system reboot.)
This flare clearly consisted of multiple peaks on timescales of
1-2 hours as usually observed in this source (also see ATel #4977),
and the 2-10 keV flux often varied by more than a factor of 2
between the scan transits.
The maximum peaks in the 2-10 keV band appeared during
the scan transits, for instance, at 06:31 (136+-11 mCrab) and
12:42 (139+-11 mCrab) on April 12. These fluxes are consistent
with the NuSTAR observation, >2.0e-9 erg/s/cm2 in the 2-10 keV
at 2013 April 12 UT 09:35, equivalent to 100 mCrab (ATel #4974).
The X-ray flux of the current flare is almost comparable to
(but not as high as) that at the historically brightest X-ray flare
observed by MAXI in February 2010, in which the maximum 6-hour
averaged 2-10 keV flux was 164+-17 mCrab (Isobe et al. PASJ 62, L55, 2010),
and the peak flux averaged over a single scan transit (~60 sec) reached
187+-18 mCrab in the 2-10 keV band.
We also note that
the hardness ratios (counts in the 4-10 keV band to those in the
2-4 keV band) were 0.73-0.90 at the flare in February 2010,
while it is 0.46 on 2013 April 12-13, indicating that the current flare
has a softer X-ray spectrum, despite of the detection of high-energy gamma-rays.
Current fluxes of this source can be seen at http://maxi.riken.jp/top/index.php?cid=000000000001&jname=J1104+382 .
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