The Origin of Diffuse X‐Ray Emission from the Galactic Ridge. I. Energy Output of Particle Sources

Abstract

We analyze processes for the hard X-ray emission from the Galactic disk, whose origin has remained enigmatic for many years. Up until now, no model has been able to explain the physical origin of this emission. Even the most plausible mechanism of bremsstrahlung radiation requires an energy output in emitting particles higher than the luminosity provided by known Galactic sources. We show that this energy enigma can be resolved if the emission comes directly from regions of particle acceleration. In this case, a broad quasi-thermal transition region of particle excess is formed between the thermal and nonthermal energy regions. The necessary energy output for production of electrons emitting 10 keV X-rays is of the order of 1041 ergs s-1, which can definitely be supplied by supernovae or other known Galactic sources of energy. The temperature of the accelerating region is restricted to a value of a few 100 eV, and plasmas with these temperatures are hydrostatically stable in the Galaxy. Since only background electrons are supposed to be accelerated, the acceleration process does not violate the state of hydrostatic equilibrium in the Galactic disk.