Large-scale variations of the cosmic X-ray background and the X-ray emissivity of the local Universe

TL;DR

This study analyzes large-scale variations in the cosmic X-ray background using RXTE data, estimating local Universe emissivity and identifying low-luminosity AGNs as primary contributors to observed anisotropies.

Contribution

It provides the first measurement of the local Universe's X-ray emissivity and links large-scale CXB variations to low-luminosity AGNs, enhancing understanding of cosmic X-ray background sources.

Findings

Detected ~2% CXB intensity variations on 20-40° scales.

Estimated local Universe X-ray emissivity at 9±4 x 10^{38} erg/sec/Mpc^{3}.

Most CXB anisotropy is due to low-luminosity AGNs.

Abstract

We study the cosmic X-ray background (CXB) intensity variations on large angular scales using slew data of the RXTE observatory. We detect intensity variations up to ~2% on angular scales of 20--40deg. These variations are partly correlated with the local large-scale structure, which allowed us to estimate the emissivity of the local Universe in the energy band 2--10 keV at 9+/-4 x 10^{38} ers/sec/Mpc^{3}. The spectral energy distribution of the large-angular-scale variations is hard and is compatible with that of the CXB, which implies that normal galaxies and clusters of galaxies, whose spectra are typically much softer, do not contribute more than 15% to the total X-ray emissivity of the local Universe. Most of the observed CXB anisotropy (after exclusion of point sources with fluxes >10^{-11} erg/s/cm^2) can be attributed to low-luminosity AGNs