The structure of the radio galaxy NGC 1265.

Data are presented on the 5-GHz polarization distribution of the head-tail radio galaxy NGC 1265 in the Perseus cluster. The data are compared with previously reported measurements at 1.4 GHz to obtain information about variations in the spectral index and the rotation and direction of the magnetic field. The reduction procedure and various uncertainties in the measurements are described. The magnetic field vectors are found to be well aligned along the tail, and the percentage of polarization attains 60% in some areas, indicating the predominance of magnetic energy. There appears to be a gradient in rotation as measured across the tail. The derived values for magnetic field strengths, electron densities, and temperatures are similar to previously reported ones, and the overall results are in agreement with the magnetospheric trail model for head-tail radio sources.