Astrophys. J., 858, 68-68 (2018/May-2)
Swift observations of Mrk 421 in selected epochs. II. An extreme spectral flux variability in 2009-2012.
KAPANADZE B., VERCELLONE S., ROMANO P., HUGHES P., ALLER M., ALLER H., KHARSHILADZE O. and TABAGARI L.
Abstract (from CDS):
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 Ep 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–1. 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.
© 2018. The American Astronomical Society. All rights reserved.
BL Lacertae objects: individual: Mrk 421
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<Available at CDS (J/ApJ/858/68): table1.dat table2.dat table5.dat table7.dat>
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