Open AccessThe origin of radio haloes and non‐thermal emission in clusters of galaxies
Author(s) -
Liang H.,
Dogiel V. A.,
Birkinshaw M.
Publication year - 2002
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1046/j.1365-8711.2002.05937.x
Subject(s) - physics , astrophysics , bremsstrahlung , electron , radio halo , compton scattering , equipartition theorem , galaxy cluster , intracluster medium , relativistic particle , coma cluster , population , magnetic field , halo , galaxy , nuclear physics , demography , quantum mechanics , sociology
We study the origin of the non‐thermal emission from the intracluster medium, including the excess hard X‐ray emission and cluster‐wide radio haloes, through fitting two representative models to the Coma cluster. If the synchrotron‐emitting relativistic electrons are accelerated in situ from the vast pool of thermal electrons, then a quasi‐stationary solution of the kinetic equation with particle acceleration through turbulence at high energies (>200 keV) naturally produces a population of suprathermal electrons responsible for the excess hard X‐ray emission through bremsstrahlung. Inverse Compton scattering is negligible at hard X‐ray energies in this case. The radio halo flux density constrains the magnetic field strength to a value close to that of equipartition, ∼1 μG . Alternatively, if the relativistic electrons are injected from numerous localized ‘external’ sources, then the hard X‐rays are best explained by inverse Compton scattering from GeV electrons, and little of the hard X‐radiation has a bremsstrahlung origin. In this case, the magnetic field strength is constrained to ∼0.1–0.2 μG . Both models assume that the non‐thermal emissions are generated by a single electron spectrum, so that only two free parameters, well constrained by the observed hard X‐ray and radio halo spectra, are needed in either case. Measurements of the cluster magnetic field will distinguish between the models.