Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002apj...581.1071m&link_type=abstract
The Astrophysical Journal, Volume 581, Issue 2, pp. 1071-1079.
Astronomy and Astrophysics
Astronomy
21
Acceleration Of Particles, Ism: Cosmic Rays, Galaxy: Disk, Ism: Structure, Stars: Supernovae: General, X-Rays: Ism
Scientific paper
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 (6.5-3.4)×10-3 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.
Dogiel Vladimir A.
Inoue Hajime
Masai Kuniaki
Schonfelder Volker
Strong Andrew W.
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