A STUDY OF NON-THERMAL RADIO EMISSION FEATURES USING FINE SPECTRAL BAO AND HIGH-SENSITIVITY RATAN OBSERVATIONS OF A SOLAR ACTIVE REGION

Abstract

Based on spectral observations of active region NOAA 8545 on 19 May 1999, we describe the processes responsible for non-thermal long-lasting radio emission and for narrow-band non-drifting bursts observed at the same time. Non-thermal long-lasting radio emission consisted of two components: short-duration (1–2 s) microbursts with fluxes about 0.001 s.f.u. and continuum emission with growing spectrum in the range of 1000–2000 MHz. Energetic electrons continuously existed in the active region for more than 2.2 hours. The nature and parameters of microbursts were discussed by Bogod, Mercier, and Yasnov (2001). Here we consider the continuum source nature. It is shown that the model, taking into account the cyclotron loss-cone instability of hot electrons and the generation of plasma waves at the upper hybrid frequency, may explain the observed continuum source parameters. For the narrow-band non-drifting bursts we consider two models: the first taking into account an excitation of weak shock waves across the magnetic field and the second with an excitation of the upper hybrid waves under the double plasma resonance. Continuum source parameters are close to the last model. Our estimations for the magnetic field strength are as follows: H=120–126 G, which is valid for the region where the electron density of background plasmas n=(1.4–1.9) ×109 cm−3; H=180–190 G for the region where n=(3.0–4.3) ×109 cm−3; H=290 G for the region where ne=2.5×1010 cm−3; and H=350 G for the region where ne=3.5×1010 cm−3. The speed of the fast electrons is about 0.10–0.14 c.