How gas-dynamic flare models powered by Petschek reconnection differ from those with ad hoc energy sources

TL;DR

This study compares gas-dynamic flare models driven by Petschek reconnection with traditional static models with ad hoc energy sources, revealing significant early differences and implications for observed solar flare emissions.

Contribution

It introduces a self-consistent reconnection-driven flare model and demonstrates its differences from ad hoc heating models, especially in early flare dynamics.

Findings

Reconnection-driven models produce higher densities at the loop top during the first minute.

Significant differences in kinetic energy and density distribution are observed early in the flare.

Loop-top density enhancements relate to slow magnetosonic shocks in Petschek's reconnection scenario.

Abstract

Aspects of solar flare dynamics, such as chromospheric evaporation and flare light-curves, have long been studied using one-dimensional models of plasma dynamics inside a static flare loop, subjected to some energy input. While extremely successful at explaining the observed characteristics of flares, all such models so far have specified energy input ad hoc, rather than deriving it self-consistently. There is broad consensus that flares are powered by magnetic energy released through reconnection. Recent work has generalized Petschek's basic reconnection scenario, topological change followed by field line retraction and shock heating, to permit its inclusion into a one-dimensional flare loop model. Here we compare the gas dynamics driven by retraction and shocking to those from more conventional static loop models energized by ad hoc source terms. We find significant differences during the first minute, when retraction leads to larger kinetic energies and produces higher densities at the loop top, while ad hoc heating tends to rarify the loop top. The loop-top density concentration is related to the slow magnetosonic shock, characteristic of Petschek's model, but persists beyond the retraction phase occurring in the outflow jet. This offers an explanation for observed loop-top sources of X-ray and EUV emission, with advantages over that provided by ad hoc heating scenarios. The cooling phases of the two models are, however, notably similar to one another, suggesting observations at that stage will yield little information on the nature of energy input.