The spatial distribution and spectral characteristics of the diffuse soft X-ray background

Abstract

The diffuse emission in soft X-rays (0.1-2.5 keV) was measured over half the sky with 5° (FWHM) spatial resolution during a sky survey experiment. X-ray intensity maps in galactic coordinates are presented in B(0.1-0.19 keV), L(0.1-0.28KeV), and M(0.4-0.9 keV) energy bands. The maps contain observations from part of the sky bounded by galactic longitudes l=180° to 270° and galactic latitudes b=40° to 80°, which is poorly studied in other surveys. Regions of excess soft X-ray emission are found to be associated with an edge of Loop I and its extension in the Southern galactic hemisphere, the northern H_I hole and other features in H_I and radio continuum surveys. No quantitative correlation is observed between the X-ray intensity and natural hydrogen column density (N_H). The energy spectra observed from some regions otside the Loop I are best fitted with thermal emission spectra of a hot plasma with cosmic elemental abundances, negligible interstellar absorption and temperature 10^6.2-10^6.3K. The observed emission measures over several regions of sky are in the range of (0.27-1.0) 10⁻² cm⁻⁶ pc. Present data support the local origin for the soft X-ray background from a thermal plasma of presure ≳4600 cm⁻³ K, temperature ~10⁶ K and size ≲330 pc. A spread in the temperature of the local hot plasma with cosmic elemental abundances, is necessary to explain the observed variation in the hardness ratio.