IMPULSIVE, STOCHASTIC, AND SHOCK WAVE ACCELERATION OF RELATIVISTIC PROTONS IN LARGE SOLAR EVENTS OF 1989 SEPTEMBER 29, 2000 JULY 14, 2003 OCTOBER 28, AND 2005 JANUARY 20

Abstract

Using the data from neutron monitors and applying various techniques, the parameters of relativistic solar protons (RSPs) outside the magnetosphere are currently being derived by several research groups. Such data, together with direct proton measurements from balloons and spacecraft, allow the determination of particle energy spectra near the Earth's orbit in successive moments of time. Spectra of RSPs in a number of large solar events tend to indicate the existence of multistep acceleration at/near the Sun. In this paper, we study the generation of RSP by neutral current sheet, stochastic, and shock-wave acceleration, within the framework of two-component concepts for ground level enhancements (GLEs) of solar cosmic rays (SCRs). Our analysis is extended to large solar events (GLEs) of 1989 September 29, 2000 July 14, 2003 October 28, and 2005 January 20. We found two different particle populations (components) in the relativistic energy range: a prompt component (PC), characterized by an early impulselike intensity increase, hard spectrum and high anisotropy, and a delayed component, presenting a gradual late increase, soft spectrum and low anisotropy. Based on a two-source model for SCR spectrum formation at the Sun, we carried out theoretical calculations of spectra in the sources for both components. We conclude that the processes in neutral current sheet, together with stochastic acceleration in expanding magnetic trap in the solar corona, are able to explain the production of two different relativistic components. Shock acceleration in the presence of coronal mass ejection (CME) fits fairly only the nonrelativistic range of the SCR spectrum, but fails in the description of relativistic proton spectra, especially for the PC.