Evidence for a Common Source of Fragmented Decimeter Emission and Meter Wave Type II Bursts in Some Solar Type IV Bursts

Abstract

The paper presents facts of relevance for flare particle acceleration and shock wave excitation in the solar corona from a detailed analysis of meter wave (40–800 MHz OSRA Tremsdorf spectrograms) and microwave data (3.1–50 GHz Polarimeter records Bern University) of several type IV bursts. We argue for a slowly uprising (about 0.1 of the local Alfvén speed) quasi-periodically acting (1… 3 min period) accelerator in the 10¹¹…10⁹ cm^-3 density region. It produces particles emitting patches of fragmented decimetric/metric radio emission. One of the quasi-periodically appearing patches is associated with the microwave burst emission, the same (or a later, lower frequency one) immediately preceeds the meter wave type II burst lanes. Therefore the onset of the patch source seems to induce also the MHD-like disturbance which can steepen to the type II burst emitting shock. In some events the fragmented patches in the frequency — time plane show a linear spreading toward lower and higher frequencies. This can be a signature of an accelerated movement. Our interpretation of the data allows to understand some of the timing and location problems between the type II shockfront and other CME or flare components.