First evidence of diffuse ultra-steep-spectrum radio emission surrounding the cool core of a cluster. Issue 2 (2nd May 2018)

• Record Type: Journal Article
• Authors: Savini, F; Bonafede, A; Brüggen, M; van Weeren, R; Brunetti, G; Intema, H; Botteon, A; Shimwell, T; Wilber, A; Rafferty, D; Giacintucci, S; Cassano, R; Cuciti, V; de Gasperin, F; Röttgering, H; Hoeft, M; White, G
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 478:Issue 2(2018)
• Page Start: 2234
• Page End: 2242
• Publication Date: 2018-05-02
• Subjects: Galaxies: clusters: individual: PSZ1G139.61+24.20; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/sty1125
• Languages: English
• ISSNs: 0035-8711

Abstract

ABSTRACT: Diffuse synchrotron radio emission from cosmic ray electrons is observed at the centre of a number of galaxy clusters. These sources can be classified either as giant radio haloes, which occur in merging clusters, or as mini haloes, which are found only in cool-core clusters. In this paper, we present the first discovery of a cool-core cluster with an associated mini halo that also shows ultra-steep-spectrum emission extending well beyond the core that resembles radio halo emission. The large-scale component is discovered thanks to LOFAR observations at 144 MHz. We also analyse GMRT observations at 610 MHz to characterize the spectrum of the radio emission. An X-ray analysis reveals that the cluster is slightly disturbed, and we suggest that the steep-spectrum radio emission outside the core could be produced by a minor merger that powers electron re-acceleration without disrupting the cool core. This discovery suggests that, under particular circumstances, both a mini halo and giant halo could co-exist in a single cluster, opening new perspectives for particle acceleration mechanisms in galaxy clusters.