On the Study of Stationary Type IV Radio Sources

Carolina Salas Matamoros, Center of Space Research, University of Costa Rica

The conditions of the Solar System medium are governed by the solar activity, CMEs are the magnetic structures that mostly affect the geomagnetic field causing geomagnetic storms at the Earth. During their evolution in the solar corona, CMEs are usually associated to radio sources, which are related to the magnetic configuration of the solar corona. In particular, stationary type IV radio bursts are associated to electrons trapped in close magnetic configurations, more often observed at the place of the CME eruption. Since the CME magnetic structure remains rooted to the Sun close to the place of post-flare loops, in this work we aim to investigate if the stationary type IV emission comes from the base of the CME structure, and if electrons are emitted via plasma emission. We conducted a detailed analysis of radio observations (Nançay Radio Heliograph and Nançcay Decametre Array, ARTEMIS, Wind/Waves spectrograph), remote-sensing observations of the corona in extreme ultraviolet (EUV) and white light as well as time histories of SXR flux measurements by GOES satellites in the 0.1-0.8 nm, to study the evolution of eight radio sources and to identify the emission mechanism associated to them. We found that stationary type IV sources were, effectively, located at the post-flare loops structures, that they presented substantial polarisation degree as well as high values of brightness temperature which confirms that emission mechanism associated to these sources is plasma emission. Since the emission mechanism was identified, we also investigated their polarisation sense in order to provide an estimation of the orientation of the CME flux rope in the corona. We found that the results are consistent with the magnetic field orientation measured in the photosphere. Because the direction of the CME flux rope is one of the most relevant properties for space weather forecasting, this work presents the polarisation of stationary type IV radio sources as a potential tool to derive the orientation of their flux ropes in the solar corona.