Stochastic particle acceleration and the problem of backgroud plasma overheating

Abstract

The origin of hard X-ray (HXR) excess emission from clusters of galaxies is still an enigma, whose nature is debated. One of the possible mechanism to produce this emission is the bremsstrahlung model. However, previous analytical and numerical calculations showed that in this case the intracluster plasma had to be overheated very fast because suprathermal electrons emitting the HXR excess lose their energy mainly by Coulomb losses, i.e., they heat the background plasma. It was concluded also from these investigations that it is problematic to produce emitting electrons from a background plasma by stochastic (Fermi) acceleration because the energy supplied by external sources in the form of Fermi acceleration is quickly absorbed by the background plasma. In other words the Fermi acceleration is ineffective for particle acceleration. We revisited this problem and found that at some parameter of acceleration the rate of plasma heating is rather low and the acceleration tails of non-thermal particles can be generated and exist for a long time while the plasma temperature is almost constant. We showed also that for some regime of acceleration the plasma cools down instead of being heated up, even though external sources (in the form of external acceleration) supply energy to the system. The reason is that the acceleration withdraws effectively high energy particles from the thermal pool (analogue of Maxwell demon).

37 pages, 10 figures, accepted by Astrophysical Journal (this version has a slightly longer introduction than the one accepted by ApJ)

References in corpus (8)

• Origin of the Fermi Bubble
• Fermi gamma-ray `bubbles' from stochastic acceleration of electrons
• Nonthermal phenomena in clusters of galaxies
• INTEGRAL discovery of non-thermal hard X-ray emission from the Ophiuchus cluster
• Nonthermal hard X-ray excess in the Coma cluster: resolving the discrepancy between the results of different PDS data analyses
• The Fermi Bubble as a Source of Cosmic Rays in the Energy Range > 10E15 eV
• Galaxy Clusters in the Swift/BAT era II: 10 more Clusters detected above 15 keV
• In-situ acceleration of subrelativistic electrons in the Coma halo and the halo's influence on the Sunyaev-Zeldovich effect

Cited by in corpus (6)

• Cosmic rays in galaxy clusters and their non-thermal emission
• Turbulence and Particle Acceleration in Giant Radio Haloes: the Origin of Seed Electrons
• Multi-wavelength Emission from the Fermi Bubble III. Stochastic (Fermi) Re-Acceleration of Relativistic Electrons Emitted by SNRs
• Multi-wavelength Emission from the Fermi Bubble I. Stochastic acceleration from Background Plasma
• Sources and Radiations of the Fermi Bubbles
• Origin of Nonthermal Emission from the Fermi Bubbles and Mechanisms of Particle Acceleration There