Proton acceleration in a single-loop disrupted during collision of two moving solitary magnetic kinks

Abstract

Abstract.We investigate a new model of single-loop flare based on the fact that a magnetic flux tube with axial current can be explosively disrupted during collision of two moving solitary magnetic kinks (MoSMaK), particularly paying attention to an acceleration mechanism of high energy protons. By using three-dimensional electromagnetic fields obtained from a resistive three-dimensional MHD equations during the single-loop flare, we investigate the orbit of many protons to obtain their energy spectra. We found that the protons can be accelerated to γ-ray-emitting energies (>1 MeV) with double power-law spectra up to about 25 MeV. There appears a breaking point of the index of the power-law spectra from 1.8 to 2.1 near 10 MeV. The protons are accelerated mainly in one direction along the loop by the electric field produced near the three-dimensional localized current associated with the magnetic reconnection process in the disrupted loop. We study the loop disruption for two different plasma beta in the center of the loop; β = 0.5 and β = 0.05. In a high beta case (β = 0.5), the disruption of the loop is more violent than that of β = 0.05. We found that the proton acceleration for the case of β = 0.5 occurs mainly at two different regions; one is inside the loop and the other is in the upper part of the disrupting loop. However, the energy spectra of protons are very similar for both cases.

Astrophysics in 2005

“…The more we can nail down the magnetic topology of reconnection regions from direct observations, the better we can hand over the likely parameters of accelerating fields to the theoreticians. There is no shortage of theoretical models and simulations of any imaginable particle acceleration scenario, such as Fermi and betatron acceleration in collapsing magnetic traps (Bogachev & Somov 2005), particle acceleration in turbulent current sheets (Dmitruk et al 2004;Wu et al 2005c), in reconnecting current sheets (Wood & Neukirch 2005), in 2D X-points (Hamilton et al 2005), in 3D reconnecting current sheets with chaotic orbits (Efthymiopoulos et al 2005;Dalla & Browning 2005), proton acceleration in coalescing loops (Sakai & Shimada 2004 and between two colliding mov-ing solitary magnetic kinks (Sakai & Kakimoto 2004), and acceleration in field line advection models (Sokolov et al 2004), and in phase-mixing regions of shear Alfve ´n waves (Tsiklauri et al 2005a(Tsiklauri et al , 2005b. Unfortunately, the observers cannot catch up with sufficiently discriminative diagnostics.…”