Analytical Model for High Energy Power-Laws in Flare Spectra
Abstract
The mechanism that accelerates particles to the energies required to produce the observed spectra in solar flares is not well understood. Here, we propose a simple fully analytical, first-principle-based model, which produces energy spectra with power-laws at high energies. This model is based on ideas from our previous semi-analytical model (Guidoni et al. 2016), which uses large-scale contracting magnetic islands (accelerators) formed during fast reconnection in simulated solar flares to accelerate electrons, as first proposed by Drake et al. (2006) for kinetic-scale plasmoids. The goal of this simple model is to develop physical insight into the development of spectrum power-laws and energy cutoffs, not to reproduce observed events in detail. We model particles visiting a small number n of accelerators, each of which increases the temperature of its initial Maxwellian distribution by a factor r. We assume that only a small fraction f of the particles in one accelerator is transferred to another accelerator. For simplicity, all accelerators have the same f and r, as well as the same average number of particles. The spectral index and the energy cutoffs of the final particle distribution can be related to our parameters n, f, and r. We find that our model (with very few physical parameters) reproduces typical observed spectral indices for flare hard X-ray emissions with as few as 5 passages through different accelerators (n = 5) and also provides a simple and intuitive explanation to energy cutoffs.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMSH11D2907G
- Keywords:
-
- 7519 Flares;
- SOLAR PHYSICS;
- ASTROPHYSICS;
- AND ASTRONOMYDE: 7526 Magnetic reconnection;
- SOLAR PHYSICS;
- ASTROPHYSICS;
- AND ASTRONOMYDE: 7845 Particle acceleration;
- SPACE PLASMA PHYSICSDE: 7984 Space radiation environment;
- SPACE WEATHER