Abstract

Radio relics are enormous Mpc-sized synchrotron emitting sources found in the outskirts of merging galaxy clusters. It is thought that these so-called relics trace cluster merger shock waves. In this talk I will present the latest observational results in several unique new relics. The properties of these relics provide unprecendented insights into the physical properties of extremely dilute cosmic plasmas, magnetic fields, and particle acceleration in shocks. Together with simulations of cluster mergers, I will demonstrate how relics can be used to probe the intracluster medium at large distances from the cluster centre and reconstruct the mass ratio, impact parameter and orientation, of cluster merger events. In addition, I will present the first high angular resolution observation of several clusters below 50 MHz from the new LOFAR telescope. LOFAR , the Low Frequency Array, is a pan-European radio telescope that is currently being commissioned. With its enormous sensitivity at the lowest frequencies it will be the breakthrough instrument for observations of diffuse radio emission in clusters.