Long Duration Flare Emission: Impulsive or Gradual Heating?

TL;DR

This study investigates long-duration solar flare emissions, proposing a two-phase heating model involving impulsive and gradual heating, supported by hydrodynamic simulations, to explain observed EUV and X-ray signatures.

Contribution

It introduces a two-phase heating scenario for long-duration flares, combining impulsive and gradual heating, supported by detailed modeling and analysis of observational data.

Findings

Each flare thread undergoes impulsive and gradual heating phases.

Modeling supports the two-phase heating scenario for long-duration flares.

Multiple threads within a single loop contribute to extended emission signatures.

Abstract

Flare emissions in X-ray and EUV wavelengths have previously been modeled as the plasma response to impulsive heating from magnetic reconnection. Some flares exhibit gradually evolving X-ray and EUV light curves, which are believed to result from superposition of an extended sequence of impulsive heating events occurring in different adjacent loops or even unresolved threads within each loop. In this paper, we apply this approach to a long duration two-ribbon flare SOL2011-09-13T22 observed by the Atmosphere Imaging Assembly (AIA). We find that to reconcile with observed signatures of flare emission in multiple EUV wavelengths, each thread should be heated in two phases, an intense impulsive heating followed by a gradual, low-rate heating tail that is attenuated over 20-30 minutes. Each AIA resolved single loop may be composed of several such threads. The two-phase heating scenario is supported by modeling with both a zero-dimensional and a 1D hydrodynamic code. We discuss viable physical mechanisms for the two-phase heating in a post-reconnection thread.