Three-dimensional Forward-fit Modeling of the Hard X-Ray and the Microwave Emissions of the 2015 June 22 M6.5 Flare

TL;DR

This study develops a 3D forward-fit model combining HXR and MW data of a solar flare using NLFFF extrapolation and GX Simulator, revealing a unified electron population with a broken power-law spectrum and trapped electrons contributing to MW emission.

Contribution

It introduces a comprehensive 3D modeling approach that simultaneously reproduces HXR and MW emissions, addressing previous spectral inversion limitations.

Findings

The electron spectrum fits a broken power-law with E_break ~ 200 keV.

The model includes an 'HXR invisible' electron population trapped above flare loops.

The approach confirms the standard flare model with consistent electron populations.

Abstract

The well-established notion of a "common population" of the accelerated electrons simultaneously producing the hard X-ray (HXR) and the microwave (MW) emission during the flare impulsive phase has been challenged by some studies reporting the discrepancies between the HXR-inferred and the MW-inferred electron energy spectra. The traditional methods of their spectral inversion have some problems that can be mainly attributed to the unrealistic and the oversimplified treatment of the flare emission. To properly address this problem, we use a Non-linear Force Free Field (NLFFF) model extrapolated from an observed photospheric magnetogram as input to the three-dimensional, multi-wavelength modeling platform GX Simulator, and create a unified electron population model that can simultaneously reproduce the observed HXR and MW observations. We model the end of the impulsive phase of the 2015-06-22 M6.5 flare, and constrain the modeled electron spatial and energy parameters using observations made by the highest-resolving instruments currently available in two wavelengths, the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) for HXR and the Expanded Owens Valley Solar Array (EOVSA) for MW. Our results suggest that the HXR-emitting electron population model fits the standard flare model with a broken power-law spectrum (E_break ~ 200 keV) that simultaneously produces the HXR footpoint emission and the MW high frequency emission. The model also includes an "HXR invisible" population of nonthermal electrons that are trapped in a large volume of magnetic field above the HXR-emitting loops, which is observable by its gyrosynchrotron (GS) radiation emitting mainly in MW low frequency range.