Non-equilibrium Ionization Modeling of Petschek-type Shocks in Reconnecting Current Sheets in Solar Eruptions

TL;DR

This study combines fast non-equilibrium ionization calculations with MHD simulations to analyze ionization properties in solar eruption reconnection sheets, revealing under-ionized features and their impact on observable diagnostics.

Contribution

It introduces a combined MHD-NEI modeling approach to study ionization dynamics in Petschek-type reconnection current sheets during solar eruptions, highlighting NEI effects on diagnostics.

Findings

Under-ionized features are common in shocked reconnection outflows.

Departure from equilibrium ionization depends on plasma density and temperature.

NEI effects significantly influence synthetic SDO/AIA intensities and inferred structures.

Abstract

Non-equilibrium ionization (NEI) is essentially required for astrophysical plasma diagnostics once the plasma status departs from ionization equilibrium assumptions. In this work, we perform fast NEI calculations combined with magnetohydrodynamic (MHD) simulations and analyze the ionization properties of a Petschek-type magnetic reconnection current sheet during solar eruptions. Our simulation reveals Petschek-type slow-mode shocks in the classical Spitzer thermal conduction models and conduction flux-limitation situations. The results show that under-ionized features can be commonly found in shocked reconnection outflows and thermal halo regions outside the shocks. The departure from equilibrium ionization strongly depends on plasma density. In addition, this departure is sensitive to the observable target temperature: the high-temperature iron ions are strongly affected by NEI effects. The under-ionization also affects the synthetic SDO/AIA intensities, which indicates that the reconstructed hot reconnection current sheet structure may be significantly under-estimated either for temperature or apparent width. We also perform the MHD-NEI analysis on the reconnection current sheet in the classical solar flare geometry. Finally, we show the potential reversal between the under-ionized and over-ionized state at the lower tip of reconnection current sheets where the downward outflow collides with closed magnetic loops, which can strongly affect multiple SDO/AIA band ratios along the reconnection current sheet.