Abstract
The synchrotron hump of the high energy peaked blazars generally lies in the 0.1â10 keV range and such sources show extreme flux and spectral variability in X-ray bands. Various spectral studies showed that the X-ray spectra of high energy peaked blazars are curved and better described by the log-parabolic model. The curvature is attributed to the energy dependent statistical acceleration mechanism. In this work, we review the X-ray spectral studies of high energy peaked blazars. It is found that the log-parabolic model well describes the spectra in a wide energy interval around the peak. The log-parabolic model provides the possibility of investigating the correlation between the spectral parameters derived from it. Therefore, we compiled the studies of correlations between the various parameters derived from the log-parabolic model and their implications to describe the variability mechanism of blazars.
Highlights
Multiwavelength observations of blazars indicate that they belong to AGNs with relativistic jets pointing close to the line of sight of observer
This flux variability is often associated with spectral variability
Interpretation of spectral variability is not very simple, as it involves many non-stable processes, such as particle acceleration, injection, cooling, and escape, which contain a number of unknown physical parameters
Summary
Multiwavelength observations of blazars indicate that they belong to AGNs (active galactic nuclei) with relativistic jets pointing close to the line of sight of observer. The variability amplitude was found to be correlated with energy, as the hardest synchrotron radiation is produced by the most energetic electrons with the smallest cooling time-scales (e.g., [8,13]) Their X-ray spectra are generally characterized by a soft (Î > 2) convex shape or by continuously downward curved shape (e.g., [9,14]), and can originate from an energy dependent particle acceleration mechanism with suitable cooling timescales (e.g., [15]). Reference [18] predicts a change in the electron spectral index by unity (0.5 for the synchrotron spectrum) around a break energy, whose value decreases with time For this reason, curved spectra have been modeled by means of other complex functions, such as double broken power law or two power laws.
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