Nonthermal Excess at Cluster Peripheries

Using confusion subtracted Green Bank Telescope observations at 1.4 GHz we have discovered that most of the diffuse synchrotron emission in two galaxy clusters is missing in the existing interferometer images. A2142 (z=0.09), a mini-halo cluster with a sloshing cool core, now displays a >1 Mpc giant radio halo spanning an X-ray cold front offering a view of physical conditions in the very different environs on either side. The radio relic in A1367 (z=0.02) extends ∼400 kpc in our GBT observations (>4× the extent previously observed). This suggests that a significant fraction of the relativistic plasma in cluster environs is undetected. Probing the relationship between the thermal and nonthermal cluster gas is crucial to understanding the associated shock/accretion/merger processes.