Particle acceleration and transport in reconnecting twisted loops in a stratified atmosphere

Abstract

Twisted coronal loops should be ubiquitous in the solar corona. Twisted magnetic fields contain excess magnetic energy, which can be released during magnetic reconnection, causing solar flares. The aim of this work is to investigate magnetic reconnection, and particle acceleration and transport in kink-unstable twisted coronal loops, with a focus on the effects of resistivity, loop geometry and atmospheric stratification. Another aim is to perform forward-modelling of bremsstrahlung emission and determine the structure of hard X-ray sources. We use a combination of magnetohydrodynamic (MHD) and test-particle methods. First, the evolution of the kinking coronal loop is considered using resistive MHD model, incorporating atmospheric stratification and loop curvature. Then, the obtained electric and magnetic fields and density distributions are used to calculate electron and proton trajectories using a guiding-centre approximation, taking into account Coulomb collisions. It is shown that electric fields in twisted coronal loops can effectively accelerate protons and electrons to energies up to 10 MeV. High-energy particles have hard, nearly power-law energy spectra. The volume occupied by high-energy particles demonstrates radial expansion, which results in the expansion of the visible hard X-ray loop and a gradual increase in hard X-ray footpoint area. Synthesised hard X-ray emission reveals strong footpoint sources and the extended coronal source, whose intensity strongly depends on the coronal loop density.

References in corpus (3)

• Recurrent solar jets in active regions
• Density structure of an active region and associated moss using Hinode/EIS
• Observational Evidence for Coronal Twisted Flux Rope

Cited by in corpus (13)

• Non-Equilibrium Processes in the Solar Corona, Transition Region, Flares, and Solar Wind \textit{(Invited Review)}
• 3He-Rich Solar Energetic Particles in Helical Jets on the Sun
• Fractional Transport in Strongly Turbulent Plasmas
• Imaging and Spectroscopic Observations of a Transient Coronal Loop: Evidence for the Non-Maxwellian $\kappa$-Distributions
• Three-dimensional dynamics of strongly twisted magnetar magnetospheres: Kinking flux tubes and global eruptions
• Particle acceleration at a reconnecting magnetic separator
• Signatures of the non-Maxwellian $\kappa$-distributions in optically thin line spectra. II. Synthetic Fe XVII--XVIII X-ray coronal spectra and predictions for the Marshall Grazing-Incidence X-ray Spectrometer (MaGIXS)
• Oscillatory reconnection and waves driven by merging magnetic flux ropes in solar flares
• Stochastic Fermi Energization of Coronal Plasma during explosive magnetic energy release
• Particle acceleration with anomalous pitch angle scattering in 2D MHD reconnection simulations
• Octupolar out-of-plane magnetic field structure generation during collisionless magnetic reconnection in a stressed X-point collapse
• Pulsations of microwave emission from a solar flare in a twisted loop caused by intrinsic MHD oscillations
• Probing Twisted Magnetic Field Using Microwave Observations in an M Class Solar Flare on 11 February, 2014