The Solar Decimetric Spike Burst of 2006 December 6: Possible Evidence for Field-Aligned Potential Drops in Post-Eruption Loops

A 1.4 GHz solar radio burst associated with a 3B/X6 eruptive flare on 2006 December 6 had the highest peak flux density (∼10 6 sfu) of any event yet recorded at this frequency. The decimetric event characteristics during the brightest emission phase (numerous intense, short-lived, narrow-band bursts that overlapped to form a continuous spectrum) suggest electron cyclotron maser (ECM) emission. The peak 1.4 GHz emission did not occur during the flare impulsive phase but rather ∼45 minutes later, in association with post-eruption loop activity seen in Hα and by the Hinode EUV Imaging Spectrometer. During the Waves/LASCO era, three other delayed bursts with peak intensities >10 5 sfu in the 1.0–1.6 GHz ( L -band) frequency range have been reported that appear to have characteristics similar to the December 6 burst. In each of these three cases, high-frequency type IV bursts were reported in a range from ∼150 to ∼1500 MHz. Assuming a common ECM emission mechanism across this frequency range implies a broad span of source heights in the associated post-eruption loop systems. Difficulties with an ECM interpretation for these events include the generation of the lower frequency component of the type IVs and the long-standing problem of escape of the ECM emission from the loops. Magnetic-field-aligned potential drops, analogous to those observed for Earth's auroral kilometric radiation, could plausibly remove both of these objections to ECM emission.