Solar type II radio bursts associated with CME expansions as shown by EUV waves

Abstract

Aims. We investigate the physical conditions of the sources of two metric type II bursts associated with coronal mass ejection (CME) expansions with the aim of verifying the relationship between the shocks and the CMEs by comparing the heights of the radio sources and of the extreme-ultraviolet (EUV) waves associated with the CMEs. Methods. The heights of the EUV waves associated with the events were determined in relation to the wave fronts. The heights of the shocks were estimated by applying two different density models to the frequencies of the type II emissions and compared with the heights of the EUV waves. For the event on 13 June 2010 that included band-splitting, the shock speed was estimated from the frequency drifts of the upper and lower frequency branches of the harmonic lane, taking into account the H/F frequency ratio f H /f F = 2. Exponential fits on the intensity maxima of the frequency branches were more consistent with the morphology of the spectrum of this event. For the event on 6 June 2012 that did not include band-splitting and showed a clear fundamental lane on the spectrum, the shock speed was directly estimated from the frequency drift of the fundamental emission, determined by linear fit on the intensity maxima of the lane. For each event, the most appropriate density model was adopted to estimate the physical parameters of the radio source. Results. The event on 13 June 2010 had a shock speed of 590-810 km s -1, consistent with the average speed of the EUV wave fronts of 610 km s -1. The event on 6 June 2012 had a shock speed of 250-550 km s -1, also consistent with the average speed of the EUV wave fronts of 420 km s -1. For both events, the heights of the EUV wave revealed to be compatible with the heights of the radio source, assuming a radial propagation of the type-II-emitting shock segment.