Combined Modeling of Acceleration, Transport, and Hydrodynamic Response in Solar Flares. I. The Numerical Model
Abstract
Acceleration and transport of highenergy particles and fluid dynamics of atmospheric plasma are interrelated aspects of solar flares, but for convenience and simplicity they were artificially separated in the past. We present here selfconsistently combined FokkerPlanck modeling of particles and hydrodynamic simulation of flare plasma. Energetic electrons are modeled with the Stanford unified code of acceleration, transport, and radiation, while plasma is modeled with the Naval Research Laboratory flux tube code. We calculated the collisional heating rate directly from the particle transport code, which is more accurate than those in previous studies based on approximate analytical solutions. We repeated the simulation of Mariska et al. with an injection of power law, downwardbeamed electrons using the new heating rate. For this case, a ~10% difference was found from their old result. We also used a more realistic spectrum of injected electrons provided by the stochastic acceleration model, which has a smooth transition from a quasithermal background at low energies to a nonthermal tail at high energies. The inclusion of lowenergy electrons results in relatively more heating in the corona (versus chromosphere) and thus a larger downward heat conduction flux. The interplay of electron heating, conduction, and radiative loss leads to stronger chromospheric evaporation than obtained in previous studies, which had a deficit in lowenergy electrons due to an arbitrarily assumed lowenergy cutoff. The energy and spatial distributions of energetic electrons and bremsstrahlung photons bear signatures of the changing density distribution caused by chromospheric evaporation. In particular, the density jump at the evaporation front gives rise to enhanced emission, which, in principle, can be imaged by Xray telescopes. This model can be applied to investigate a variety of highenergy processes in solar, space, and astrophysical plasmas.
 Publication:

The Astrophysical Journal
 Pub Date:
 September 2009
 DOI:
 10.1088/0004637X/702/2/1553
 arXiv:
 arXiv:0906.2449
 Bibcode:
 2009ApJ...702.1553L
 Keywords:

 acceleration of particles;
 hydrodynamics;
 methods: numerical;
 Sun: chromosphere;
 Sun: flares;
 Sun: Xrays;
 gamma rays;
 Astrophysics  Solar and Stellar Astrophysics
 EPrint:
 Accepted by ApJ (2009 June 12), 15 page, 12 figures