The Hard X-ray emission of the blazar PKS 2155--304

TL;DR

This study analyzes the X-ray emission of the blazar PKS 2155-304 from 2009 to 2014, revealing spectral curvature and a hard X-ray excess that supports a spine/layer jet structure model over a one-zone model.

Contribution

It provides detailed spectral analysis of PKS 2155-304's X-ray emission and interprets the hard X-ray excess within a spine/layer jet framework, advancing understanding of jet structures in blazars.

Findings

Spectral curvature observed in most XMM-Newton observations.

Hard X-ray excess explained by inverse Comptonization in a spine/layer jet model.

X-ray spectral features vary with intensity states.

Abstract

The synchrotron peak of the X-ray bright High Energy Peaked Blazar (HBL) PKS 2155$-$304 occurs in the UV-EUV region and hence its X-ray emission (0.6--10 keV) lies mostly in the falling part of the synchrotron hump. We aim to study the X-ray emission of PKS 2155$-$304 during different intensity states in 2009$-$2014 using XMM$-$Newton satellite. We studied the spectral curvature of all of the observations to provide crucial information on the energy distribution of the non-thermal particles. Most of the observations show curvature or deviation from a single power-law and can be well modeled by a log parabola model. In some of the observations, we find spectral flattening after 6 keV. In order to find the possible origin of the X-ray excess, we built the Multi-band Spectral Energy distribution (SED). We find that the X-ray excess in PKS 2155--304 is difficult to fit in the one zone model but, could be easily reconciled in the spine/layer jet structure. The hard X-ray excess can be explained by the inverse Comptonization of the synchrotron photons (from the layer) by the spine electrons.