Flare Models of Magnetic Energy Release into Plasma Heating and Particle Acceleration

Abstract:

Understanding how flare magnetic energy can be released at rates of the order of 10^27-32 ergs/s has been a long-sought goal in Heliophysics. Indirect observations of the lower solar corona point to magnetic reconnection as the fundamental process that converts free magnetic energy mainly into flows, heat, and particle acceleration. The partitioning among these three energies is usually inferred indirectly from subsequent radiation emitted by heated plasma and energetic particles, but the uncertainties are large. The energy conversion to bulk motion and heat can be reasonably well described with magnetohydrodynamic (MHD) models and simulations, while kinetic models are better suited to study particle energization. However, the scale separation between MHD and kinetic regimes in flares is approximately 10 orders of magnitude. Therefore, it is currently impossible to self-consistently unify flare models over all relevant scales.

We present results of our analytical 1D model of the super-Alfvénic shortening of reconnected field lines (reconnection outflow) and the consequent plasma heating by strong gas-dynamic shocks formed by this fast retraction. We also describe our efforts to bridge the theoretical gap between MHD and kinetic regimes by combining global flare simulations and analytical kinetic theory to produce power-law–like particle energy spectra. This model explains key characteristics of observed flare hard X-ray spectra, as well as the underlying accelerated-electron properties.