2002ApJ...581.1071M -
Astrophys. J., 581, 1071-1079 (2002/December-3)
The origin of diffuse X-ray emission from the galactic ridge. II. Nonequilibrium emission due to in situ electrons.
MASAI K., DOGIEL V.A., INOUE H., SCHONFELDER V. and STRONG A.W.
Abstract (from CDS):
The origin of the Galactic ridge X-ray emission has been investigated from various points of view, such as the iron K line, the hard part of the continuum, and energetics. We propose a ridge plasma model based on stochastic particle acceleration in the interstellar medium to explain the properties of the soft and hard X-rays consistently. In situ accelerated electrons form a spectrum that consists of three components: bulk thermal (Maxwellian), quasi-thermal, and nonthermal (power law) through diffusion in momentum space. For the bulk temperature of a few hundred eV, the quasi-thermal component extends up to a few tens of keV. While nonthermal electrons are collisionless, so as to stay in the acceleration regime, quasi-thermal electrons interact with the bulk electrons through Coulomb collisions. Thus, the interaction with the bulk plasma significantly alters the X-ray emission, and the resultant spectrum can explain the observed features that resemble the emission from a multitemperature or nonequilibrium plasma of order of keV. From a comparison of the model predictions with the observed spectrum, we found that the Galactic ridge X-ray emission is explained by electron acceleration in interstellar gas with temperature 0.3-0.6 keV and density 6.5-3.4x10–3 cm–3, which can be bound by Galactic gravity. This model can also solve the energetics problem: since a substantial part of the X-ray flux is accounted for by nonequilibrium emission due to quasi-thermal electrons of a small fraction of the medium, we need neither hot plasmas of the order of keV nor higher rates of supernova explosion in the Galaxy to explain the ridge X-ray emission.
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Journal keyword(s):
Acceleration of Particles - ISM: Cosmic Rays - Galaxy: Disk - ISM: Structure - Stars: Supernovae: General - X-Rays: ISM
Simbad objects:
2
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