The sub-arcsecond hard X-ray structure of loop footpoints in a solar flare

Abstract

The newly developed X-ray visibility forward fitting technique is applied to Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) data of a limb flare to investigate the energy and height dependence on sizes, shapes, and position of hard X-ray chromospheric footpoint sources. This provides information about the electron transport and chromospheric density structure. The spatial distribution of two footpoint X-ray sources is analyzed using PIXON, Maximum Entropy Method, CLEAN and visibility forward fit algorithms at nonthermal energies from $\sim 20$ to $\sim 200$ keV. We report, for the first time, the vertical extents and widths of hard X-ray chromospheric sources measured as a function of energy for a limb event. Our observations suggest that both the vertical and horizontal sizes of footpoints are decreasing with energy. Higher energy emission originates progressively deeper in the chromosphere consistent with downward flare accelerated streaming electrons. The ellipticity of the footpoints grows with energy from $\sim 0.5$ at $\sim 20$ keV to $\sim 0.9$ at $\sim 150$ keV. The positions of X-ray emission are in agreement with an exponential density profile of scale height $\sim 150$~km. The characteristic size of the hard X-ray footpoint source along the limb is decreasing with energy suggesting a converging magnetic field in the footpoint. The vertical sizes of X-ray sources are inconsistent with simple collisional transport in a single density scale height but can be explained using a multi-threaded density structure in the chromosphere.

7 pages, 7 figures, submitted to ApJ

References in corpus (9)

• High Resolution Observations and Modeling of Dynamic Fibrils
• Chromospheric magnetic field and density structure measurements using hard X-rays in a flaring coronal loop
• RHESSI Observation of Chromospheric Evaporation
• Combined Modeling of Acceleration, Transport, and Hydrodynamic Response in Solar Flares: I. The Numerical Model
• Stereoscopic electron spectroscopy of solar hard X-ray flares with a single spacecraft
• A Statistical Survey of Hard X-ray Spectral Characteristics of Solar Flares with Two Footpoints
• Hard X-ray Spectra and Positions of Solar Flares observed by RHESSI: photospheric albedo, directivity and electron spectra
• The effect of wave-particle interactions on low energy cutoffs in solar flare electron spectra
• Exploring the connection between coronal and footpoint sources in a thin-thick target solar flare model

Cited by in corpus (39)

• Implications of X-ray Observations for Electron Acceleration and Propagation in Solar Flares
• Solar science with the Atacama Large Millimeter/submillimeter Array - A new view of our Sun
• Implications for electron acceleration and transport from non-thermal electron rates at looptop and footpoint sources in solar flares
• Turbulent pitch-angle scattering and diffusive transport of hard-X-ray producing electrons in flaring coronal loops
• Magnetic Reconnection During the Post-Impulsive Phase of a Long-Duration Solar Flare: Bi-Directional Outflows as a Cause of Microwave and X-ray Bursts
• Acceleration, magnetic fluctuations and cross-field transport of energetic electrons in a solar flare loop
• Pre-flare activity and magnetic reconnection during the evolutionary stages of energy release in a solar eruptive flare
• FOXSI-2: Upgrades of the Focusing Optics X-ray Solar Imager for its Second Flight
• Observing the formation of flare-driven coronal rain
• Effect of collisions and magnetic convergence on electron acceleration and transport in reconnecting twisted solar flare loops
• Blowout Jets and Impulsive Eruptive Flare in a Bald-Patch Topology
• RHESSI and SDO/AIA observations of the chromospheric and coronal plasma parameters during a solar flare
• The Low-High-Low Trend of Type III Radio Burst Starting Frequencies and Solar Flare Hard X-rays
• Height structure of X-ray, EUV and white-light emission in a solar flare
• Diffusive Transport of Energetic Electrons in the Solar Corona: X-ray and Radio Diagnostics
• The spectral difference between solar flare HXR coronal and footpoint sources due to wave-particle interactions
• Electron Distribution Functions in Solar Flares from combined X-ray and EUV Observations
• Spatially resolved hard X-ray polarization in solar flares: effects of Compton scattering and bremsstrahlung
• Hard X-ray footpoint sizes and positions as diagnostics of flare accelerated energetic electrons in the low solar atmosphere
• Statistically-derived flaring chromospheric-coronal density structure from non-thermal X-ray observations of the Sun
• Turbulent cross-field transport of non-thermal electrons in coronal loops: theory and observations
• The Role of Energy Diffusion in the Deposition of Energetic Electron Energy in Solar and Stellar Flares
• Numerical simulations of chromospheric hard X-ray source sizes in solar flares
• Probing Dynamics of Electron Acceleration with Radio and X-ray Spectroscopy, Imaging, and Timing in the 2002 Apr 11 Solar Flare
• Frequency rising sub-THz emission from solar flare ribbons
• The influence of albedo on the size of hard X-ray flare sources
• High-temperature differential emission measure and altitude variations in the temperature and density of solar flare coronal X-ray sources
• Temporal variations of X-ray solar flare loops: length, corpulence, position, temperature, plasma pressure and spectra
• Statistical study of hard X-ray emitting electrons associated with flare-related coronal jets
• Spatio-temporal energy partitioning in a non-thermally dominated two-loop solar flare
• LOFAR observations of radio burst source sizes and scattering in the solar corona
• Arcade Implosion Caused by a Filament Eruption in a Flare
• Coronal Heating Law Constrained by Microwave Gyroresonant Emission
• Cassini and extra force constraints to nonminimally coupled gravity with screening mechanism
• Spectral and Imaging Diagnostics of Spatially-Extended Turbulent Electron Acceleration and Transport in Solar Flares
• The RHESSI Microflare Height Distribution
• Estimates of Densities and Filling Factors from a Cooling Time Analysis of Solar Microflares Observed with RHESSI
• Plasma dynamics in the flaring loop observed by RHESSI
• RESIK and RHESSI observations of the 20 September 2002 flare