Free access article

A&A 436, 711-717 (2005)
DOI: 10.1051/0004-6361:20052716

Proton acceleration and its energy spectra during the coalescence of two cross current loops

J. I. Sakai and K. Shimada

Laboratory for Plasma Astrophysics Faculty of Engineering, Toyama University, 3190 Gofuku, Toyama 930-8555, Japan
    e-mail: sakaijun@eng.toyama-u.ac.jp

(Received 17 January 2005 / Accepted 7 February 2005 )

Abstract
We investigate plasma dynamics during coalescence of two cross current loops by using a resistive three-dimensional MHD simulation code, paying particular attention to finding the most effective electromagnetic fields for producing high-energy protons. Next we investigate the orbit of many protons in the electromagnetic fields obtained from the MHD simulations and find that proton acceleration is more efficient compared with the case of two parallel loops coalescing. It is shown that the maximum proton energy is about 25 MeV, which exceeds the energy (2.223 MeV) of the observed prompt nuclear de-excitation lines of gamma-ray and that the proton energy spectrum is a power-law type with an index of about 2-2.3. The simulation results imply that proton-associated gamma-ray sources are located near the footpoints with magnetic north polarity. We found that strong proton acceleration leading to the observed prompt line gamma-ray emissions can be realized only when both poloidal and axial magnetic fields reconnect completely.

Key words: Sun: flares -- magnetohydrodynamics (MHD) -- methods: numerical -- acceleration of particles

© ESO 2005

The OpenURL standard is a protocol for transmission of metadata describing the resource that you wish to access. An OpenURL link contains article metadata and directs it to the OpenURL server of your choice. The OpenURL server can provide access to the resource and also offer complementary services (specific search engine, export of references...). The OpenURL link can be generated by different means.

• If your librarian has set up your subscription with an OpenURL resolver, OpenURL links appear automatically on the abstract pages.
• You can define your own OpenURL resolver with your EDPS Account. In this case your choice will be given priority over that of your library.
• You can use an add-on for your browser (Firefox or I.E.) to display OpenURL links on a page (see http://www.openly.com/openurlref/). You should disable this module if you wish to use the OpenURL server that you or your library have defined.