Giant events in the 23rd solar cycle: Common and specific features

Abstract

Giant X-ray events (>X17) in the 23rd solar cycle (October 28 and November 4, 2003, and September 7, 2005) are considered, which were almost completely observed in hard X rays (>150 keV) from the INTEGRAL satellite and partly from the RHESSI satellite. These events are compared with two events completely observed from the RHESSI satellite (X8.2 on November 2, 2003, and X7.1 on January 20, 2005). Time profiles of the plasma temperature, calculated from the GOES data on soft X rays during these events, have similar structures. This allowed us to choose a zero time point in each event and compare the dynamics of their evolution. Nonthermal radiation began approximately 10 min before the zero time point (preflare phase). During about 20 min after the zero point, bursts of nonthermal radiation were observed in all the three events, which pointed to several episodes of electron acceleration with variable spectra and plasma heating with different efficiency. It is shown that giant events are characterized by a large emission measure and a relatively low temperature of the flare plasma but not intensive acceleration processes. Observations of γ radiation from the decay of π0-mesons show that protons are accelerated to relativistic energies 4 min after the chosen zero point.