Properties of the Acceleration Regions in Several Loop-structured Solar Flares

Abstract

Using {\em RHESSI} hard X-ray imaging spectroscopy observations, we analyze electron flux maps for a number of extended coronal loop flares. For each event, we fit a collisional model with an extended acceleration region to the observed variation of loop length with electron energy $E$, resulting in estimates of the plasma density in, and longitudinal extent of, the acceleration region. These quantities in turn allow inference of the number of particles within the acceleration region and hence the filling factor $f$ -- the ratio of the emitting volume to the volume that encompasses the emitting region(s). We obtain values of $f$ that lie mostly between 0.1 and 1.0; the (geometric) mean value is $f=0.20\times ÷3.9$, somewhat less than, but nevertheless consistent with, unity. Further, coupling information on the number of particles in the acceleration region with information on the total rate of acceleration of particles above a certain reference energy (obtained from spatially-integrated hard X-ray data) also allows inference of the specific acceleration rate (electron s${}^{-1}$ per ambient electron above the chosen reference energy). We obtain a (geometric) mean value of the specific acceleration rate $\eta (20$ keV) $=(6.0\times /÷3.4)\times 10^{-3}$ electrons s${}^{-1}$ per ambient electron; this value has implications both for the global electrodynamics associated with replenishment of the acceleration region and for the nature of the particle acceleration process.

References in corpus (1)

• A Classification Scheme For Turbulent Acceleration Processes In Solar Flares

Cited by in corpus (38)

• Global Energetics of Thirty-Eight Large Solar Eruptive Events
• Simulations of the Mg II k and Ca II 8542 lines from an Alfvén Wave-heated flare chromosphere
• Electron Power-Law Spectra in Solar and Space Plasmas
• Global Energetics of Solar Flares: III. Non thermal Energies
• MEM_GE: a new maximum entropy method for image reconstruction from solar X-ray visibilities
• Thermal-nonthermal energy partition in solar flares derived from X-ray, EUV, and bolometric observations
• A simple model of chromospheric evaporation and condensation driven conductively in a solar flare
• On the variation of solar flare coronal x-ray source sizes with energy
• Suppression of parallel transport in turbulent magnetized plasmas and its impact on non-thermal and thermal aspects of solar flares
• Investigating the differential emission measure and energetics of microflares with combined SDO/AIA and RHESSI observations
• Large-scale contraction and subsequent disruption of coronal loops during various phases of the M6.2 flare associated with the confined flux rope eruption
• 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
• The role of diffusion in the transport of energetic electrons during solar flares
• A count-based imaging model for the Spectrometer/Telescope for Imaging X-rays (STIX) in Solar Orbiter
• Forward-fitting STIX visibilities
• Global Energetics of Solar Flares: VIII. The Low-Energy Cutoff
• The Specific Acceleration Rate in Loop-structured Solar Flares -- Implications for Electron Acceleration Models
• Heating and cooling of coronal loops with turbulent suppression of parallel heat conduction
• Revealing evolution of nonthermal electrons in solar flares using 3D modeling
• Coronal Loop Scaling Laws for Various Forms of Parallel Heat Conduction
• Connecting Chromospheric Condensation Signatures to Reconnection Driven Heating Rates in an Observed Flare
• High-temperature differential emission measure and altitude variations in the temperature and density of solar flare coronal X-ray sources
• Rapid Variability in the SOL2011-08-04 Flare: Implications for Electron Acceleration
• Coronal hard X-ray sources revisited
• Temporal variations of X-ray solar flare loops: length, corpulence, position, temperature, plasma pressure and spectra
• Validation Of The Coronal Thick Target Source Model
• Electron distribution and energy release in magnetic reconnection outflow regions during the pre-impulsive phase of a solar flare
• A Very Narrow RHESSI X-ray Flare on 25 September 2011
• Flare Energy Release in the Magnetic Field Polarity Inversion Line During M1.2 Solar Flare of March 15, 2015. Paper I. Onset of Plasma Heating and Electrons Acceleration
• The efficiency of electron acceleration during the impulsive phase of a solar flare
• Identification of multiple hard X-ray sources in solar flares: A Bayesian analysis of the February 20 2002 event
• Coronal Thick Target Hard X Ray Emissions and Radio Emissions
• Return currents and energy transport in the solar flaring atmosphere
• Modelling of Nonthermal Microwave Emission From Twisted Magnetic Loops
• Probing Twisted Magnetic Field Using Microwave Observations in an M Class Solar Flare on 11 February, 2014
• Observation of 2011-02-15 X2.2 flare in Hard X-ray and Microwave
• Energy release in the solar atmosphere from a stream of infalling prominence debris