Energy Spectra of the Soft X-ray Diffuse Emission in Fourteen Fields Observed with Suzaku

TL;DR

This study analyzes the soft X-ray diffuse emission in fourteen Galactic fields observed with Suzaku, revealing correlations between oxygen line intensities, their relation to Galactic temperature, and estimating the Galaxy's diffuse X-ray luminosity.

Contribution

It provides new measurements of soft X-ray emission spectra across multiple fields, clarifies the origins of oxygen line emissions, and estimates the Galaxy's diffuse X-ray luminosity and temperature.

Findings

O VII and O VIII intensities are well correlated.

O VII emission shows an intensity floor at ~2 LU.

Galactic diffuse emission temperature is around 0.2 keV.

Abstract

The soft diffuse X-ray emission of twelve fields observed with Suzaku are presented together with two additional fields from previous analyses. All have galactic longitudes 65 deg < l < 295 deg to avoid contributions from the very bright diffuse source that extends at least 30 deg from the Galactic center. The surface brightnesses of the Suzaku nine fields for which apparently uncontaminated ROSAT All Sky Survey (RASS) were available were statistically consistent with the RASS values, with an upper limit for differences of 17 x 10^{-6} c s^{-1} amin^{-2} in R45}-band. The Ovii and Oviii intensities are well correlated to each other, and Ovii emission shows an intensity floor at ~2 photons s^{-1} cm^{-2 str^{-1} (LU). The high-latitude Oviii emission shows a tight correlation with excess of Ovii emission above the floor, with (Oviii intensity) = 0.5 x [(Ovii intensity) -2 LU], suggesting that temperatures averaged over different line-of-sight show a narrow distribution around ~0.2 keV. We consider that the offset intensity of Ovii arises from the Heliospheric solar wind charge exchange and perhaps from the local hot bubble, and that the excess Ovii (2-7 LU) is emission from more distant parts of the Galaxy. The total bolometric luminosity of this galactic emission is estimated to be 4 x 10^{39} erg s^{-1}, and its characteristic temperature may be related to the virial temperature of the Galaxy.