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

Stroe, Andra and Rumsey, Clare and Harwood, Jeremy J. and Van weeren, Reinout J. and Röttgering, Huub J. A. and Saunders, Richard D. E. and Sobral, David and Perrott, Yvette C. and Schammel, Michel P. (2014) The highest frequency detection of a radio relic : 16 GHz AMI observations of the 'Sausage' cluster. Monthly Notices of the Royal Astronomical Society: Letters, 441 (1): slu045. L41-L45. ISSN 1745-3925

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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 intracluster 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 ± 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.

Item Type:
Journal Article
Journal or Publication Title:
Monthly Notices of the Royal Astronomical Society: Letters
Uncontrolled Keywords:
?? acceleration of particlesradiation mechanisms: non-thermalradio continuum: generalshock wavesgalaxies: clusters: individual: ciza j2242.8+5301astronomy and astrophysicsspace and planetary science ??
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Deposited On:
15 Jan 2016 12:00
Last Modified:
15 Jul 2024 15:43