Identification of a Peculiar Radio Source in the Aftermath of Large Coronal Mass Ejection Events

We report the discovery of a new radio feature associated with coronal mass ejection (CME) events. The feature is a low-frequency (<1 MHz), relatively wide (~300 kHz) continuum that appears just after the main phase of the eruptive event, lasts for several hours, and exhibits a slow negative frequency drift. So far, we have identified this radio signature in a handful of CME events and suspect it might be a common occurrence. The radio continuum starts almost simultaneously with the commonly observed decimetric type IV stationary continuum (also called flare continuum), but the two seem unrelated. The emission mechanism, whether plasma emission or gyroresonance, is unclear at the moment. On the basis of our preliminary analysis, we interpret this radio continuum as the lateral interaction of the CME with magnetic structures. Another possibility is that this continuum traces the reconfiguration of large-scale loop systems, such as streamers. In other words, it could be the large-scale counterpart of the post-CME arcades seen over active region neutral lines after big CME events. This Letter aims to bring attention to this feature and attract more research into its nature.