Search

The Faraday rotation measures of a sample of extragalactic radio sources projected within a third of an Abell radius of a galaxy cluster were compared with those of sources located further from cluster centers. The result strongly indicates that the distribution of the residual rotation measure (RRM) in the former population is broadened, at a confidence level exceeding 99%. The broadening is detectable out to 1h 50 −1 Mpc. Our best estimate of the excess Faraday rotation measure varies from 100±36 rad m −2 in the central sixth of an Abell radius to 36±15 rad m −2 further out. The combination of these results with electron densities determined from X-ray data for some of the clusters suggests that magnetic field strengths in cluster gas are of order 1 microgauss

New observations of the radio emission from the Coma cluster of galaxies have revealed the most detailed image of an intergalactic halo yet seen in a cluster of galaxies. The centroid of the halo emission is significantly displaced from that of the X-ray emission. The Faraday rotation of polarized emission from background radio sources has been measured. There is a significant contribution to the rotation measure (RM) of sources seen through the cluster. The excess RM, when combined with the X-ray data, has allowed direct measurement of the magnetic-field strength, at about 2 microG, providing an independent check of the widely used assumption of equipartition between the energy in relativistic particles and that in the magnetic field. The observations also allow an estimate of the degree of tangling of the cluster magnetic field. The magnetic field reversals seem to occur on a scale size of 13-40 kpc. The extent of the halo emission and the degree of field tangling indicate that the radio halo source must be sustained by particle reacceleration in the intracluster medium. 50 refs.

The results of an attempt to probe the magnetoionic strength of the supernova remnant OA 184 (G166.2 + 2.5) by measuring the Faraday rotation measures of background radio sources in the field are described. The data reveal a systematic sign flip of the RMs within and/or around the SNR. The background RMs are consistent with an interstellar magnetic irregularity scale of the order of 100 pc. 16 references.