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Swift/BAT finds hard X-Ray flaring activity correlated with an ongoing TeV flare of Mrk421

ATel #11195; Matthias Kadler (U. Wuerzburg) and H. A. Krimm (NSF)
on 18 Jan 2018; 01:52 UT
Credential Certification: David M. Palmer (palmer@lanl.gov)

Subjects: X-ray, Gamma Ray, TeV, Black Hole, Blazar, Transient

Referred to by ATel #: 11199, 11216

The Swift/BAT hard X-ray transient monitor reports the detection of ongoing flaring activity from the high-energy peaked BL Lac type object Mrk 421 in the 15-50 keV range. Examination of the data (https://swift.gsfc.nasa.gov/results/transients/weak/Mrk421/) shows the source at a level of >8 sigma on two consecutive days:
0.0101+-0.0012 ct/s/cm2 (46 mCrab) on 2018-Jan-15 (MJD 58133) and
0.0130+-0.0016 ct/s/cm2 (59 mCrab) on 2018-Jan-16 (MJD 58134).
An examination of the BAT light curve before this bright flare shows a high-flux state at >3 sigma significance between Jan 10-12, 2018
(0.0032+-0.0010 ct/s/cm2, 0.0030+-0.0009 ct/s/cm2, and 0.0049+-0.0011 ct/s/cm2, respectively).

Ongoing flaring activity of Mrk421 at TeV energies was already reported since December 2017 by the FACT and HAWC collaboration (ATels #11077 and #11086). An exceptional flare was reported by FACT at TeV energies between between 1:15 UTC and 7:05 UTC on Jan 17 (MJD 58135) with a maximum of>10 CU and a decrease towards the end of the night.