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|Title:||Swift Observations of Mrk 421 in Selected Epochs. II. An Extreme Spectral Flux Variability in 2009-2012||Authors:||Kapanadze, B.
|Issue Date:||2018||Journal:||THE ASTROPHYSICAL JOURNAL||Number:||858||Issue:||2||First Page:||68||Abstract:||We present the results from a detailed spectral and timing study of Mrk 421 based on the rich archival Swift data obtained during 2009-2012. Best fits of the 0.3-10 keV spectra were mostly obtained using the log-parabolic model showing the relatively low spectral curvature that is expected in the case of efficient stochastic acceleration of particles. The position of the synchrotron spectral energy density peak E <SUB>p</SUB> of 173 spectra is found at energies higher than 2 keV. The photon index at 1 keV exhibited a very broad range of values a = 1.51-3.02, and very hard spectra with a < 1.7 were observed during the strong X-ray flares, hinting at a possible hadronic jet component. The spectral parameters varied on diverse timescales and showed a correlation in some periods, which is expected in the case of first- and second-order Fermi acceleration. The 0.3-10 keV flux showed strong X-ray flaring activity by a factor of 3-17 on timescales of a few days-weeks between the lowest historical state and that corresponding to a rate higher than 100 cts s<SUP>-1</SUP>. Moreover, 113 instances of intraday variability were revealed, exhibiting shortest flux-doubling/halving times of about 1.2 hr, as well as brightenings by 7%-24% in 180-720 s and declines by 68%-22% in 180-900 s. The X-ray and very high-energy fluxes generally showed a correlated variability, although one incidence of a more complicated variability was also detected, indicating that the multifrequency emission of Mrk 421 could not be generated in a single zone.||URI:||http://hdl.handle.net/20.500.12386/28420||URL:||https://iopscience.iop.org/article/10.3847/1538-4357/aabbac||ISSN:||0004-637X||DOI:||10.3847/1538-4357/aabbac||Bibcode ADS:||2018ApJ...858...68K||Fulltext:||open|
|Appears in Collections:||1.01 Articoli in rivista|
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checked on Jan 19, 2021
checked on Jan 19, 2021
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