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Swift/BAT observations of the X-ray flare from Mrk 421

ATel #4983; H. A. Krimm (CRESST/GSFC/USRA), S. D. Barthelmy (GSFC), W. Baumgartner (CRESST/GSFC/UMBC), J. Cummings (CRESST/GSFC/UMBC), N. Gehrels (GSFC), A. Y. Lien (NASA/GSFC/ORAU), C. B. Markwardt (GSFC), D. Palmer (LANL), T. Sakamoto (AGU), M. Stamatikos (OSU/GSFC), T. Ukwatta (MSU)
on 16 Apr 2013; 18:20 UT
Credential Certification: Hans A. Krimm (Hans.Krimm@nasa.gov)

Subjects: X-ray, Blazar, Transient

Referred to by ATel #: 5021

The Swift/BAT team reports that the current flare from the blazar Markarian 421 is strongly detected in the BAT hard X-ray transient monitor. In the 15-50 keV energy band of the monitor, renewed activity from Mrk 421 began on 2013 April 12 (MJD 56394) when the source reached a one-day average rate of 0.006 +/- 0.0008 ct/s/cm^2 (30 mCrab), rising to a one-day average rate of 0.012 +/- 0.0009 ct/s/cm^2 (55 mCrab) on April 15. In the orbital light curves, we see two flares, the first lasting from approximately April 12 21:57 UT to April 13 10:16 and peaking at ~40 mCrab and then a stronger flare lasting from approximately April 15 02:23 UT to April 15 15:32 and peaking at 160 mCrab. The count rate was near baseline (~0.002 ct/s/cm^2 or 7 mCrab) before, between and after these events.

The first flare started somewhat after the activity reported by NuStar (Balokovic et al, ATel #4974) and MAXI (Negoro et al, ATel #4978) and is also delayed relative to the onset of activity in the VHE (Cortina & Holder, ATel #4976) and Fermi/LAT (Paneque et al, ATel #4977) who reported flaring activity as early as April 11 and April 9, respectively. The peak BAT rate is comparable to what was seen in July 2006 (though the 2006 flare lasted four days), March 2008 (Krimm et al, ATel #1449), November 2009 (Krimm et al, ATel #2292 and February 2010.

Swift/BAT Hard X-ray Transient light curve for Mrk 421