3 years ago

Hard X-ray properties of NuSTAR blazars.

Gopal Bhatta, Illya Bilinsky, Maksym Mohorian

We present the results of our study on the hard X-ray properties of the NuSTAR blazars. We carried out timing, spectral and cross-correlation analysis of 31 NuSTAR observations of 13 blazars. We investigated the spectral shapes of the sources using single power-law, broken power-law and log-parabola models. We found that for most of the sources the hard X-ray emission can be well represented by single power-law model; and that the spectral slopes for different blazar sub-classes are consistent with so called "blazar sequence". We report a steepest spectra ($\Gamma\sim3$) in the BL Lacertae PKS 2155--304 and a hardest spectra ($\Gamma\sim1.4$) in the flat-spectrum radio quasar PKS 2149--306. In addition, we noted a close connection between the flux and spectral slope within the source sub-class in the sense that high flux and/or flux states tend to be harder in spectra. We also found the signatures of soft and hard lags of a few ours, and a complex relation between the flux and the hardness ratio. Using the minimum variability timescales, we infer the distribution of the emission region sizes. In BL Lacertae objects, assuming particle acceleration by diffusive shocks and synchrotron cooling as the dominant processes governing the observed flux variability, we constrain the magnetic field of the emission region to be a few gauss; whereas in flat-spectrum radio quasars, using external Compton models, we estimate the energy of the lower end of the injected electrons to be a few hundreds of Lorentz factors.

Publisher URL: http://arxiv.org/abs/1710.09910

DOI: arXiv:1710.09910v1

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