The solar decimetric spike burst of 2006 december 6: Possible evidence for field-aligned potential drops in post-eruption loops

Abstract

A 1.4GHz solar radio burst associated with a 3B/X6 eruptive flare on 2006 December 6 had the highest peak flux density (106sfu) 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 1.4GHz 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 >105sfu in the 1.0-1.6GHz (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 1500MHz. 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. © 2011. The American Astronomical Society. All rights reserved.