Transition Region and Chromospheric Signatures of Impulsive Heating Events. II. Modeling

Abstract

Results from the Solar Maximum Mission showed a close connection between the hard X-ray and transition region emission in solar flares. Analogously, the modern combination of RHESSI and IRIS data can inform the details of heating processes in ways never before possible. We study a small event that was observed with RHESSI, IRIS, SDO, and Hinode, allowing us to strongly constrain the heating and hydrodynamical properties of the flare, with detailed observations presented in a previous paper. Long duration red-shifts of transition region lines observed in this event, as well as many other events, are fundamentally incompatible with chromospheric condensation on a single loop. We combine RHESSI and IRIS data to measure the energy partition among the many magnetic strands that comprise the flare. Using that observationally determined energy partition, we show that a proper multi-threaded model can reproduce these red-shifts in magnitude, duration, and line intensity, while simultaneously being well constrained by the observed density, temperature, and emission measure. We comment on the implications for both RHESSI and IRIS observations of flares in general, namely that: (1) a single loop model is inconsistent with long duration red-shifts, among other observables; (2) the average time between energization of strands is less than 10 seconds, which implies that for a hard X-ray burst lasting ten minutes, there were at least 60 strands within a single IRIS pixel located on the flare ribbon; (3) the majority of these strands were explosively heated with energy distribution well described by a power law of slope $\approx -1.6$; (4) the multi-stranded model reproduces the observed line profiles, peak temperatures, differential emission measure distributions, and densities.

10 pages, 8 figures. Accepted to ApJ

References in corpus (10)

• Highly Efficient Modeling of Dynamic Coronal Loops
• RHESSI Microflare Statistics II. X-ray Imaging, Spectroscopy & Energy Distributions
• Evidence of Non-Thermal Particles in Coronal Loops Heated Impulsively by Nanoflares
• Imaging and spectroscopic observations of magnetic reconnection and chromospheric evaporation in a solar flare
• Transition Region and Chromospheric Signatures of Impulsive Heating Events. I. Observations
• Solar Flare Element Abundances from the Solar Assembly for X-rays (SAX) on MESSENGER
• Properties of chromospheric evaporation and plasma dynamics of a solar flare from IRIS observations
• Fractal Reconnection in Solar and Stellar Environments
• Collisional and Radiative Processes in Optically Thin Plasmas
• Direct observation of the energy release site in a solar flare by SDO/AIA, Hinode/EIS and RHESSI

Cited by in corpus (12)

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• Hydrogen Balmer Line Broadening in Solar and Stellar Flares
• Formation of the thermal infrared continuum in solar flares
• Transition Region and Chromospheric Signatures of Impulsive Heating Events. I. Observations
• Nonequilibrium ionization and ambipolar diffusion in solar magnetic flux emergence processes
• Solar Flare Arcade Modelling: Bridging the gap from 1D to 3D Simulations of Optically Thin Radiation
• Spectroscopic Observations of Magnetic Reconnection and Chromospheric Evaporation in an X-shaped Solar Flare
• The direct relation between the duration of magnetic reconnection and the evolution of GOES light curves in solar flares
• Connecting Chromospheric Condensation Signatures to Reconnection Driven Heating Rates in an Observed Flare
• Diagnosing the Optically Thick/Thin Features Using the Intensity Ratio of Si IV Resonance Lines in Solar Flares
• A new view of the solar interface region from the Interface Region Imaging Spectrograph (IRIS)
• Infrared spectropolarimetry of a C-class solar flare footpoint plasma -- I. Spectral features and forward modelling