An X-ray view of the INTEGRAL/IBIS blazars

TL;DR

This study uses broad-band X-ray observations from INTEGRAL, Swift, and XMM-Newton to analyze 9 blazars, revealing spectral flattening at low energies, absence of certain features, and a correlation between absorption and redshift, enhancing understanding of blazar properties.

Contribution

It provides the first comprehensive broad-band spectral analysis of a sample of 9 blazars, confirming the N_H-z trend and characterizing the absorption and spectral properties across different redshifts.

Findings

Spectral flattening observed below 3 keV in all sources.

No significant Compton reflection features detected.

Higher absorption (N_H) at z>2 confirmed with a larger sample.

Abstract

Aim of this work is a broad-band study with INTEGRAL, Swift and XMM-Newton satellites of a sample of 9 blazars (7 FSRQ and 2 BL Lac) with redshift up to about 4. The spectral analysis has shown clear evidence of a flattening of the continuum towards the low energies ($E<3$ keV observer frame). This behaviour is well reproduced both with an absorbed power-law model ($N_H\sim10^{20}$-$10^{23}$ cm$^{-2}$ in the rest-frame of the sources) or a broken power-law continuum model (with an energy break below 3 keV in the observer-frame). No Compton reflection features, Fe $K\alpha$ line and hump at high energies, have been detected, with the exception of the source IGR J22517+2218 that shows the presence of a weak iron line. In this work we also investigate a possible correlation between the absorption column density $N_H$ and the red-shift. We confirm the existence of a $N_H$-z trend, with the higher absorption at z$>$2 for a larger sample compared to previous results. The distribution of the $N_H$ and the photon index $\Gamma$ is also presented. The hard X-ray data allow us to detect highly absorbed sources (with $N_H\ge10^{23}$cm$^{-2}$ in rest-frame of the source) characterized by photon index distribution peaked at harder values ($\Gamma\sim1.4$) with respect to that obtained with XMM data only ($\Gamma\sim2$).