First observation of a transitioning Type II solar radio burst and the effects of scattering on split-band Type II sources

Nicolina Chrysaphi - University of Glasgow, United Kingdom

Session: The solar sources of space weather

Abstract

Shock waves can excite radio emissions which reflect the shock’s speed, known as Type II solar radio bursts.  Drifting Type II bursts are often associated to CME-driven shocks that propagate through the corona, but stationary Type II bursts with no frequency-drift rate have also been observed.  The fundamental and harmonic bands of a Type II burst can further split into thinner lanes, a phenomenon known as “band splitting”, the origins of which are debated.  Using high-resolution LOFAR observations, we observed the first Type II burst that transitions from a stationary to a drifting state, reporting a new sub-class of Type II bursts referred to as “transitioning” Type II bursts.  The generation mechanism of the transitioning Type II burst was related to the eruption of a coronal jet that produced a steamer-puff CME.  The spatial separation observed between the subband sources of split-band Type II bursts was also investigated.  It was found that the imaged separation of ∼0.2+/-0.05 R_solar between two sources at 32 and 40 MHz can be attributed to the shift that radio sources experience due to scattering.  As such, band-splitting models that require the intrinsic sources of a split-band Type II burst to be virtually co-spatial are supported.