Radio relics are patches of diffuse synchrotron radio emission that trace shock waves. Relics are thought to form when intra-cluster medium electrons are accelerated by cluster merger induced shock waves through the diffusive shock acceleration mechanism. In this paper, we present observations spanning 150 MHz to 30 GHz of the 'Sausage' and 'Toothbrush' relics from the Giant Metrewave and Westerbork telescopes, the Karl G. Jansky Very Large Array, the Effelsberg telescope, the Arcminute Microkelvin Imager and Combined Array for Research in Millimeter-wave Astronomy. We detect both relics at 30 GHz, where the previous highest frequency detection was at 16 GHz. The integrated radio spectra of both sources clearly steepen above 2 GHz, at the 6σ significance level, supports the spectral steepening previously found in the 'Sausage' and the Abell 2256 relic. Our results challenge the widely adopted simple formation mechanism of radio relics and suggest more complicated models have to be developed that, for example, involve re-acceleration of aged seed electrons.

The Arcminute Microkelvin Imager is a pair of interferometer arrays operating with six frequency channels spanning 13.9-18.2 GHz, for observations on angular scales of 30 arcsec-10 arcmin and for declinations greater than −15 • ; the Small Array has a sensitivity of 30 mJy s −1/2 and the Large Array has a sensitivity of 3 mJy s −1/2 . The telescope is aimed principally at Sunyaev-Zel'dovich imaging of clusters of galaxies. We discuss the design of the telescope and describe and explain its electronic and mechanical systems.

We report new cm‐wave measurements at five frequencies between 15 and 18 GHz of the continuum emission from the reportedly anomalous ‘region 4’ of the nearby galaxy NGC 6946. We find that the emission in this frequency range is significantly in excess of that measured at 8.5 GHz, but has a spectrum from 15 to 18 GHz consistent with optically thin free–free emission from an ultracompact H ii region. In combination with previously published data, we fit four emission models containing different continuum components using the Bayesian spectrum analysis package radiospec. These fits show that, in combination with data at other frequencies, a model with a spinning dust component is slightly preferred to those that possess better‐established emission mechanisms.

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We present observations using the Small Array of the Arcminute Microkelvin Imager (AMI; 14–18 GHz) of four Abell and three MACS clusters spanning 0.171–0.686 in redshift. We detect Sunyaev–Zel’dovich (SZ) signals in five of these without any attempt at source subtraction, although strong source contamination is present. With radio‐source measurements from high‐resolution observations, and under the assumptions of spherical β‐model, isothermality and hydrostatic equilibrium, a Bayesian analysis of the data in the visibility plane detects extended SZ decrements in all seven clusters over and above receiver noise, radio sources and primary cosmic microwave background imprints. Formal Bayesian evidence ratios range from 1011:1 to 1043:1 for six of the clusters and 3000:1 for one with substantially fewer data than the others. We present posterior probability distributions for, e.g., total mass and gas fraction averaged over radii internal to which the mean overdensity is 1000, 500 and 200, r200 being the virial radius. Reaching r200 involves some extrapolation for the nearer clusters but not for the more distant ones. We find that our estimates of gas fraction are low (compared with most in the literature) and decrease with increasing radius. These results appear to be consistent with the notion that gas temperature in fact falls with distance (away from near the cluster centre) out to the virial radius.