Magnetic field amplification and high-energy emission properties of compact galactic clusters

Abstract

The observed appearance of the high-energy gamma-ray emission from galactic star clusters is determined by the geometry of the cluster and the distribution of the energy sources inside the cluster. A large number of massive stars with strong winds and supernova explosions lead to the formation of multidirectional plasma flows, shocks and strong magnetohydrodynamic turbulence. Magnetic turbulence is the main factor which determine the maximal energies of the accelerated particles and the power of the source. Here we discuss an effect of the efficient magnetic field amplification at the supernova shocks due to the cosmic-ray driven plasma instabilities on the gamma-ray and neutrino fluxes from massive star clusters. We show here that the photon flux attenuation by the e± pair production is important for this kind of sources in the photon energy range 1015 — 1016 eV. The ratio of the gamma-ray to the neutrino fluxes is a declining function of the distance to the source at 5-15 kpc and the photon flux can be several times lower than the corresponding neutrino flux from the hadron interactions.