LOFAR high-band antenna observations of the Perseus cluster

Abstract

The Perseus cluster is the brightest X-ray cluster in the sky and is known as a cool-core galaxy cluster. Being a very nearby cluster, it has been extensively studied. This has provided a comprehensive view of the physical processes that operate in the intracluster medium (ICM), including feedback from the active galactic nucleus (AGN) 3C 84 and measurements of ICM turbulence. Additionally, the Perseus cluster contains a central radio mini-halo. This diffuse radio source traces cosmic-ray electrons (re-)accelerated in situ in the ICM. Here, we report on LOFAR high-band antenna 120-168 MHz observations of the Perseus cluster that probe a range of four orders of magnitude in angular scales. In our 0.3″ (0.11 kpc) resolution image, we find that the northern extension of the 3C 84 lobe consists of several narrow 1.5–3 kpc parallel strands of emission. In addition, we detect steep-spectrum filaments associated with a previous outburst of the central AGN radio emission filling two known X-ray “ghost” cavities. At 7″ resolution (2.6 kpc), our images show a complex structured radio mini-halo, with several edges and filaments. At resolutions of 26″ (10 kpc) and 80″ (29 kpc), we discover diffuse radio emission with a 1.1 Mpc extent. We classify this emission as a giant radio halo, and its properties are distinct from the inner mini-halo. We also detect two diffuse sources at projected cluster centric radii of 0.7 and 1.0 Mpc. Finally, we observe a 0.9 Mpc trail of radio emission from the cluster member galaxy IC 310 that connects it to the giant radio halo. Together with other recent studies of relaxed clusters, our LOFAR observations indicate that cluster-wide radio emission could be (more) common in cool-core clusters. In the case of the Perseus cluster, a past off-axis merger event that preserved the cool core might have generated enough turbulence to produce an extended radio halo observable at low frequencies.