The deep look onto the hard X-ray sky: The Swift - INTEGRAL X-ray (SIX) survey

TL;DR

This paper presents a highly sensitive hard X-ray survey combining Swift/BAT and INTEGRAL/IBIS data, revealing 113 sources including many AGNs, and investigates their evolution, providing valuable targets for future telescopes.

Contribution

The study introduces a novel combined survey approach that enhances sensitivity and sky coverage, improving detection of faint X-ray sources and advancing understanding of AGN evolution.

Findings

Detected 113 X-ray sources, including 86 AGNs.

No evidence of AGN evolution at redshift below 0.4.

Survey provides targets for next-generation X-ray telescopes.

Abstract

The super-massive black-holes in the centers of Active Galactic Nuclei (AGNs) are surrounded by obscuring matter that can block the nuclear radiation. Depending on the amount of blocked radiation, the flux from the AGN can be too faint to be detected by currently flying hard X-ray (above 15 keV) missions. At these energies only ~1% of the intensity of the Cosmic X-ray Background (CXB) can be resolved into point-like sources that are AGNs. In this work we address the question of the undetected sources contributing to the CXB with a very sensitive and new hard X-ray survey: the SIX survey that is obtained with the new approach of combining the Swift/BAT and INTEGRAL/IBIS X-ray observations. We merge the observations of both missions. This enhances the exposure time and reduces systematic uncertainties. As a result we obtain a new survey over a wide sky area of 6200 deg^2 that is more sensitive than the surveys of Swift/BAT or INTEGRAL/IBIS alone. Our sample comprises 113 sources: 86 AGNs (Seyfert-like and blazars), 5 galaxies, 2 clusters of galaxies, 3 Galactic sources, 3 previously detected unidentified X-ray sources, and 14 unidentified sources. The scientific outcome from the study of the sample has been properly addressed to study the evolution of AGNs at redshift below 0.4. We do not find any evolution using the 1/V_max method. Our sample of faint sources are suitable targets for the new generation hard X-ray telescopes with focusing techniques.