On the relation between solar-flare gamma-ray emission and proton escape into interplanetary space

Abstract

It is shown that escaping of solar flare energetic protons into interplanetary space as well as their relation to the flare gamma-ray emission depend on the parameter β = 8πp/B 0 2 , where p is the pressure of hot plasma and energetic particles and B 0 is the magnetic field in a flaring loop. If β≪1, the bulk of the energetic protons escape to the loss cone because of diffusion due to small-scale Alfven-wave turbulence, and precipitate into the footpoints of the flaring loop. The flare then produces intense gamma-ray line emission and a weak flux of high energy protons in interplanetary space. If β>β*≃0.3-1.0, then fast eruption of hot plasma and energetic particles out of the flaring loop occurs, this being due to the flute instability or ‘magnetic-field-plasma’ nonequilibrium. The flare then produces a comparatively weak gamma-radiation and rather intense proton fluxes in interplanetary space. We predict a modulation of the solar flare gamma-ray line emission with a period ≲ 1 s during the impulsive phase that is due to the MHD-oscillations of the energy release volume. The time lag of the gamma-ray peaks with respect to the hard X-ray peaks during a simultaneous acceleration of electrons and protons can be understood in terms of strong diffusion.