dc.contributor.author Paliya, Vaidehi S. dc.contributor.author Böttcher, Markus dc.contributor.author Diltz, Chris dc.contributor.author Stalin, C.S. dc.contributor.author Sahayanathan, S. dc.date.accessioned 2016-08-30T07:38:07Z dc.date.available 2016-08-30T07:38:07Z dc.date.issued 2015 dc.identifier.citation Paliya, V.S. et al. 2015. The violent hard X-ray variability of Mrk 421 observed by NuSTAR in 2013 April. Astrophysical journal, 811(2): Article no 143. [https://doi.org/10.1088/0004-637X/811/2/143] en_US dc.identifier.issn 0004-637X dc.identifier.issn 1538-4357 (Online) dc.identifier.uri http://hdl.handle.net/10394/18440 dc.identifier.uri https://doi.org/10.1088/0004-637X/811/2/143 dc.identifier.uri http://iopscience.iop.org/article/10.1088/0004-637X/811/2/143 dc.description.abstract The well-studied blazar Markarian 421 (Mrk 421, z = 0.031) was the subject of an intensive multi-wavelength campaign when it flared in 2013 April. The recorded X-ray and very high-energy (E > 100 GeV) γ-ray fluxes are the highest ever measured from this object. At the peak of the activity, it was monitored by the hard X-ray focusing telescope Nuclear Spectroscopic Telescope Array (NuSTAR) and the Swift X-Ray Telescope (XRT). In this work, we present a detailed variability analysis of NuSTAR and Swift-XRT observations of Mrk 421 during this flaring episode. We obtained the shortest flux doubling time of 14.01 ± 5.03 minutes, which is the shortest hard X-ray (3–79 keV) variability ever recorded from Mrk 421, and is on the order of the light-crossing time of the black hole's event horizon. A pattern of extremely fast variability events superposed on slowly varying flares is found in most of the NuSTAR observations. We suggest that these peculiar variability patterns may be explained by magnetic energy dissipation and reconnection in a fast-moving compact emission region within the jet. Based on the fast variability, we derive a lower limit on the magnetic field strength of $B\geqslant 0.73{\delta }_{1}^{-2/3}\;{\nu }_{19}^{1/3}$ G, where δ1 is the Doppler factor in units of 10, and ν19 is the characteristic X-ray synchrotron frequency in units of 1019 Hz en_US dc.language.iso en en_US dc.publisher American Astronomical Society en_US dc.subject X-rays: galaxies en_US dc.subject galaxies: active en_US dc.subject galaxies: jets en_US dc.subject quasars: individual (Mrk 421) en_US dc.title The violent hard X-ray variability of Mrk 421 observed by NuSTAR in 2013 April en_US dc.type Article en_US dc.contributor.researchID 24420530 - Böttcher, Markus
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