Emergence of hard X-rays at weak nonstationary processes in active regions

Abstract

Using Suzaku and Reuven Ramaty High Energy Solar Spectroscopic Image (RHESSI) spacecraft data, we study the characteristics of X-ray emission of weak flares at energies when this emission is generated by fluxes of accelerated electrons. Of the 105 events recorded by a broadband monitor of the entire sky (WAM/Suzaku, with an effective area of ~800 cm² in the energy range from 50 to 300 keV), we consider 64 B1to C3-class flares. The spectra of these events up to 30 keV are built from RHESSI data. We consider some examples of simultaneous recordings of weak flares occurring from 2005 to 2007. The radiation fluxes measured by WAM/Suzaku at 100 keV have been found to be consistent with those expected from the one-parameter approximation of spectra of the nonthermal radiation recorded by RHESSI at lower energies. The average spectral slope for all events under consideration is 4.30 ± 0.15; i.e., these rare events are significantly stricter than the majority of subflares. This can serve as proof of the fact that the particle acceleration in weak flares is more effective than was previously assumed. As in powerful events, these processes occur in the close vicinity of spots or in places where the neutral line separates hills with a large magnetic field strength.