Sardinia Radio Telescope observations of Abell 194 - the intra-cluster
  magnetic field power spectrum
  We study the intra-cluster magnetic field in the poor galaxy cluster Abell
194 by complementing radio data, at different frequencies, with data in the
optical and X-ray bands. We analyze new total intensity and polarization
observations of Abell 194 obtained with the Sardinia Radio Telescope (SRT). We
use the SRT data in combination with archival Very Large Array observations to
derive both the spectral aging and Rotation Measure (RM) images of the radio
galaxies 3C40A and 3C40B embedded in Abell 194. The optical analysis indicates
that Abell 194 does not show a major and recent cluster merger, but rather
agrees with a scenario of accretion of small groups. Under the minimum energy
assumption, the lifetimes of synchrotron electrons in 3C40B measured from the
spectral break are found to be 157 Myrs. The break frequency image and the
electron density profile inferred from the X-ray emission are used in
combination with the RM data to constrain the intra-cluster magnetic field
power spectrum. By assuming a Kolmogorov power law power spectrum, we find that
the RM data in Abell 194 are well described by a magnetic field with a maximum
scale of fluctuations of Lambda_max=64 kpc and a central magnetic field
strength of <B0>=1.5 microG. Further out, the field decreases with the radius
following the gas density to the power of eta=1.1. Comparing Abell 194 with a
small sample of galaxy clusters, there is a hint of a trend between central
electron densities and magnetic field strengths.
