Spectro-polarimetric observations of the CIZA J2242.8+5301 northern
  radio relic: no evidence of high-frequency steepening
  Observations of radio relics at very high frequency (>10 GHz) can help to
understand how particles age and are (re-)accelerated in galaxy cluster
outskirts and how magnetic fields are amplified in these environments. In this
work, we present new single-dish 18.6 GHz Sardinia Radio Telescope and 14.25
GHz Effelsberg observations of the well known northern radio relic of CIZA
J2242.8+5301. We detected the relic which shows a length of $\sim$1.8 Mpc and a
flux density equal to $\rm S_{14.25\,GHz}=(9.5\pm3.9)\,mJy$ and $\rm
S_{18.6\,GHz}=(7.67\pm0.90)\,mJy$ at 14.25 GHz and 18.6 GHz respectively. The
resulting best-fit model of the relic spectrum from 145 MHz to 18.6 GHz is a
power-law spectrum with spectral index $\alpha=1.12\pm0.03$: no evidence of
steepening has been found in the new data presented in this work. For the first
time, polarisation properties have been derived at 18.6 GHz, revealing an
averaged polarisation fraction of $\sim40\%$ and a magnetic field aligned with
the 'filaments' or 'sheets' of the relic.
