The highest-frequency detection of a radio relic: 16-GHz AMI observations of the `Sausage' cluster

Abstract

We observed the cluster CIZA J2242.8+5301 with the Arcminute Microkelvin Imager at $16$ GHz and present the first high radio-frequency detection of diffuse, non-thermal cluster emission. This cluster hosts a variety of bright, extended, steep-spectrum synchrotron-emitting radio sources, associated with the intra-cluster medium, called radio relics. Most notably, the northern, Mpc-wide, narrow relic provides strong evidence for diffusive shock acceleration in clusters. We detect a puzzling, flat-spectrum, diffuse extension of the southern relic, which is not visible in the lower radio-frequency maps. The northern radio relic is unequivocally detected and measures an integrated flux of $1.2\pm 0.3$ mJy. While the low-frequency ($<2$ GHz) spectrum of the northern relic is well represented by a power-law, it clearly steepens towards $16$ GHz. This result is inconsistent with diffusive shock acceleration predictions of ageing plasma behind a uniform shock front. The steepening could be caused by an inhomogeneous medium with temperature/density gradients or by lower acceleration efficiencies of high energy electrons. Further modelling is necessary to explain the observed spectrum.

Accepted for publication in MNRAS Letters. 5 pages, 2 figures, 1 table

References in corpus (2)

• Particle Acceleration on Megaparsec Scales in a Merging Galaxy Cluster
• Shock acceleration as origin of the radio relic in A521?

Cited by in corpus (13)

• Diffuse Radio Emission from Galaxy Clusters
• The rise and fall of star-formation in $\mathbf{z}\sim 0.2$ merging galaxy clusters
• MC^2: Constraining the Dark Matter Distribution of the Violent Merging Galaxy Cluster CIZA J2242.8+5301 by Piercing through the Milky Way
• MC${}^2$: Boosted AGN and star-formation activity in CIZA J2242.8+5301, a massive post-merger cluster at z=0.19
• Spectral age modelling of the `Sausage' cluster radio relic
• The radio relic in Abell 2256: overall spectrum and implications for electron acceleration
• Evidence for a pressure discontinuity at the position of the Coma relic from Planck Sunyaev-Zel'dovich effect data
• First detection at 5.5 and 9 GHz of the radio relics in bullet cluster with ATCA
• Shock Acceleration Model with Postshock Turbulence for Giant Radio Relics
• AMI SZ observation of galaxy-cluster merger CIZA J2242+5301: perpendicular flows of gas and dark matter
• AMI-CL J0300+2613: a Galactic anomalous-microwave-emission ring masquerading as a galaxy cluster
• Acceleration of cosmic rays by double shock waves in galaxy clusters: application to radio relics
• MOSS I: Double radio relics in the Saraswati supercluster