LOFAR high-band antenna observations of the Perseus cluster

The discovery of a giant radio halo

¹ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
² Centre for Extragalactic Astronomy, Department of Physics, Durham University, Durham DH1 3LE, UK
³ Institute for Computational Cosmology, Department of Physics, Durham University, South Road, Durham DH1 3LE, UK
⁴ Département de physique, de génie physique et d’optique, Université Laval, Québec, QC G1V 0A6, Canada
⁵ INAF – Istituto di Radioastronomia, via P. Gobetti 101, 40129 Bologna, Italy
⁶ Department of Physics & Astronomy, University of Waterloo, Waterloo, ON N2L 3G1, Canada
⁷ Waterloo Centre for Astrophysics, University of Waterloo, Waterloo, ON N2L 3G1, Canada
⁸ Département de Physique, Université de Montréal, Succ. Centre-Ville, Montréal, Québec, QC H3C 3J7, Canada
⁹ Dipartimento di Fisica e Astronomia, Università di Bologna, via P. Gobetti 93/2, 40129 Bologna, Italy
¹⁰ University of Hamburg, Hamburger Sternwarte, Gojenbergsweg 112, 21029 Hamburg, Germany
¹¹ INAF-IASF Milano, Via A. Corti 12, 20133 Milano, Italy
¹² ASTRON, The Netherlands Institute for Radio Astronomy, Postbus 2, 7990 AA Dwingeloo, The Netherlands

^★ Corresponding author; rvweeren@strw.leidenuniv.nl

Received: 22 July 2024
Accepted: 1 October 2024

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.