Broad-band spectral analysis of the Galactic Ridge X-ray Emission

TL;DR

This study provides a detailed broad-band spectral analysis of the Galactic Ridge X-ray Emission, supporting the idea that it mainly originates from numerous faint X-ray sources, including magnetic white dwarfs and coronal sources.

Contribution

It presents high-quality Suzaku spectra of the GRXE and confirms its origin as an assembly of faint X-ray stars through spectral modeling and comparison with previous high-resolution studies.

Findings

GRXE spectra fitted by white dwarf and thermal plasma models

Supports the scenario that GRXE is from numerous faint X-ray sources

Estimated unresolved source density consistent with previous resolved source counts

Abstract

Detailed spectral analysis of the Galactic X-ray background emission, or the Galactic Ridge X-ray Emission (GRXE), is presented. To study the origin of the emission, broad-band and high-quality GRXE spectra were produced from 18 pointing observations with Suzaku in the Galactic bulge region, with the total exposure of 1 Ms. The spectra were successfully fitted by a sum of two major spectral components; a spectral model of magnetic accreting white dwarfs with a mass of 0.66 (0.59-0.75) solar, and a softer optically-thin thermal emission with a plasma temperature of 1.2-1.5 keV which is attributable to coronal X-ray sources. When combined with previous studies which employed high spatial resolution of the Chandra satellite (e.g. Revnivtsev et al. 2009, Nature), the present spectroscopic result gives another strong support to a scenario that the GRXE is essentially an assembly of numerous discrete faint X-ray stars. The detected GRXE flux in the hard X-ray band was used to estimate the number density of the unresolved hard X-ray sources. When integrated over a luminosity range of ~10^30-10^34 erg/s, the result is consistent with a value which was reported previously by directly resolving faint point sources.