Combining the Swift/BAT and the INTEGRAL/ISGRI observations

TL;DR

This study combines INTEGRAL and Swift surveys to create a more sensitive X-ray survey, resolving over twice as much of the Cosmic X-ray Background and identifying more AGN than previous surveys.

Contribution

The paper introduces a method to merge independent X-ray surveys, significantly increasing sensitivity and resolving a larger fraction of the CXB.

Findings

Resolved more than twice the CXB compared to previous surveys.

Created a new survey covering 6200 deg2 with ~4 times the sensitivity.

Identified over 100 AGN in the combined survey.

Abstract

Current surveys of Active Galactic Nuclei (AGN) find only a very small fraction of AGN contributing to the Cosmic X-ray Background (CXB) at energies above 15 keV. Roughly 99% of the CXB is so far unresolved. In this work we address the question of the unresolved component of the CXB with the combined surveys of INTEGRAL and Swift. These two currently flying X-ray missions perform independent surveys at energies above 15 keV. Our approach is to perform the independent surveys and merge them in order to enhance the exposure time and reduce the systematic uncertainties. We do this with resampling techniques. As a result we obtain a new survey over a wide sky area of 6200 deg2 that is a factor ~4 more sensitive than the survey of Swift or INTEGRAL alone. Our sample comprises more than 100 AGN. We use the extragalactic source sample to resolve the CXB by more than a factor 2 compared to current parent surveys.