Observations of the galaxy cluster CIZA J2242.8+5301 with the Sardinia Radio Telescope

Abstract

We observed the galaxy cluster CIZA J2242.8+5301 with the Sardinia Radio Telescope to provide new constraints on its spectral properties at high frequency. We conducted observations in three frequency bands centred at 1.4 GHz, 6.6 GHz and 19 GHz, resulting in beam resolutions of 14${}^{\prime }$, 2.9${}^{\prime }$ and 1${}^{\prime }$ respectively. These single-dish data were also combined with archival interferometric observations at 1.4 and 1.7 GHz. From the combined images, we measured a flux density of ${\mathrm{S}}_{1.4GHz}=(158.3\pm 9.6)\mathrm{mJy}$ for the central radio halo and ${\mathrm{S}}_{1.4GHz}=(126\pm 8)\mathrm{mJy}$ and ${\mathrm{S}}_{1.4GHz}=(11.7\pm 0.7)\mathrm{mJy}$ for the northern and the southern relic respectively. After the spectral modelling of the discrete sources, we measured at 6.6 GHz ${\mathrm{S}}_{6.6GHz}=(17.1\pm 1.2)\mathrm{mJy}$ and ${\mathrm{S}}_{6.6GHz}=(0.6\pm 0.3)\mathrm{mJy}$ for the northern and southern relic respectively. Assuming simple diffusive shock acceleration, we interpret measurements of the northern relic with a continuous injection model represented by a broken power-law. This yields an injection spectral index ${\alpha }_{\mathrm{inj}}=0.7\pm 0.1$ and a Mach number $\mathrm{M}=3.3\pm 0.9$, consistent with recent X-ray estimates. Unlike other studies of the same object, no significant steepening of the relic radio emission is seen in data up to 8.35 GHz. By fitting the southern relic spectrum with a simple power-law (${\mathrm{S}}_{\nu }\propto {\nu }^{-\alpha }$) we obtained a spectral index $\alpha \approx 1.9$ corresponding to a Mach number ($\mathrm{M}\approx 1.8$) in agreement with X-ray estimates. Finally, we evaluated the rotation measure of the northern relic at 6.6 GHz. These results provide new insights on the magnetic structure of the relic, but further observations are needed to clarify the nature of the observed Faraday rotation.

20 pages, 11 figures. Accepted by MNRAS

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• Discovering the most elusive radio relic in the sky: Diffuse Shock Acceleration caught in the act?
• Downstream depolarization in the Sausage relic: a 1-4 GHz Very Large Array study
• A perfect power-law spectrum even at highest frequencies: The Toothbrush relic
• Turbulent magnetic fields in the merging galaxy cluster MACS J0717.5+3745: polarization analysis
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• Radio relics in PSZ2 G096.88+24.18: A connection with pre-existing plasma
• An International Survey of Front-End Receivers and Observing Performance of Telescopes for Radio Astronomy
• Sardinia Radio Telescope observations of the Coma Cluster
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