AGN variability at hard X-rays

TL;DR

This study analyzes the variability of AGN in hard X-rays above 20 keV using data from INTEGRAL and Swift/BAT, revealing differences between blazars and Seyfert galaxies and exploring spectral variability in specific sources.

Contribution

It demonstrates the potential of INTEGRAL and Swift/BAT for hard X-ray timing analysis of AGN and reports on variability patterns and spectral changes in Seyfert galaxies.

Findings

Blazars show larger variability than Seyfert galaxies.

Hard X-ray luminosity is anti-correlated with variability in Seyferts.

Spectral variability observed in IC 4329A indicates changes in the Comptonising medium.

Abstract

We present preliminary results on the variability properties of AGN above 20 keV in order to show the potential of the INTEGRAL IBIS/ISGRI and Swift/BAT instruments for hard X-ray timing analysis of AGN. The 15-50 keV light curves of 36 AGN observed by BAT during 5 years show significantly larger variations when the blazar population is considered (average normalized excess variance = 0.25) with respect to the Seyfert one (average normalized excess variance = 0.09). The hard X-ray luminosity is found to be anti-correlated to the variability amplitude in Seyfert galaxies and correlated to the black hole mass, confirming previous findings obtained with different AGN hard X-ray samples. We also present results on the Seyfert 1 galaxy IC 4329A, as an example of spectral variability study with INTEGRAL/ISGRI data. The position of the high-energy cut-off of this source is found to have varied during the INTEGRAL observations, pointing to a change of temperature of the Comptonising medium. For several bright Seyfert galaxies, a considerable amount of INTEGRAL data have already been accumulated and are publicly available, allowing detailed spectral variability studies at hard X-rays.