Numerical simulations of X rays and gamma rays from solar flares
Abstract
Radiation of energies from 10 keV to greater than 10 MeV has been observed during solar flares, and is interpreted to be due to bremsstrahlung by relativistic electrons. A complete treatment of this problem requires solution of kinetic equation for relativistic electrons and inclusion of synchrotron energy losses. This equation is solved analytically in some simple limiting cases and numerically for models which have varying densities and magnetic fields using a FokkerPlanck code developed for this purpose. The resulting electron flux distributions are then used to calculate the spectral indices and angular distributions of the radiation and these results are used to compare with Hard Xray Burst Spectrometer (HXRBS) observations of 30 to 500 keV x rays and Gamma Ray Spectrometer (GRS) observations of 0.3 to 1 MeV and greater than 10 MeV gamma rays. Assuming that electron anisotropy is independent of flare size, the distribution of GRS event fluences are derived from the distribution of HXRBS fluxes. It is also shown that a single population of injected electrons with constant energy spectral index extending from tens of keV to tens of MeV is not consistent with the observed GRS and HXRBS spectral index distributions. The observed variation of the mean spectral index with heliocentric angle is then used to set limits on the average degree of anisotropy of the pitch angle distribution of the injected electrons and the amount of convergence of the magnetic field. The results are compared with stereoscopic observations of individual flares and it is shown that some of this data cannot be reconciled with the above models.
 Publication:

Ph.D. Thesis
 Pub Date:
 1989
 Bibcode:
 1989PhDT.........8M
 Keywords:

 Bremsstrahlung;
 Gamma Rays;
 Solar Flares;
 Solar Radiation;
 Solar XRays;
 Anisotropy;
 Energy Dissipation;
 FokkerPlanck Equation;
 High Energy Electrons;
 Kinetic Equations;
 Magnetic Effects;
 Mathematical Models;
 Relativistic Particles;
 Solar Physics