Astronomy and Astrophysics, volume 489, 69-83 (2008/10-1)
Deep Westerbork observations of Abell 2256 at 350 MHz.
Abstract (from CDS):
Deep polarimetric Westerbork observations of the galaxy cluster Abell 2256 are presented, covering a frequency range of 325-377MHz. The central halo source has a diameter of the order of 1.2Mpc (18'), which is somewhat larger than at 1.4GHz. With α=-1.61±0.04, the halo spectrum between 1.4GHz and 22.25MHz is less steep than previously thought. The centre of the ultra steep spectrum source in the eastern part of the cluster exhibits a spectral break near 400MHz. It is estimated to be at least 51 million years old, but possibly older than 125 million years. A final measurement requires observations in the 10-150MHz range. It remains uncertain whether the source is a radio tail of Fabricant galaxy 122, situated in the northeastern tip of the source. Faraday rotation measure synthesis revealed no polarized flux at all in the cluster. The polarization fraction of the brightest parts of the relic area is less than 1%. The RM-synthesis nevertheless revealed 9 polarized sources in the field enabling an accurate measurement of the Galactic Faraday rotation (-33±2rad/m2 in front of the relic). Based on its depolarization on longer wavelengths, the line-of-sight magnetic field in relic filament G is estimated to be between 0.02 and 2µG. A value of 0.2µG appears most reasonable given the currently available data.
galaxies: clusters: individual: Abell 2256 - magnetic fields - polarization - radio continuum: general
Fig.11, Table 3: [B2008] NN (Nos 1-11).