An Attempt to detect Linearly Polarized Radio Emmision from the Galaxy

Abstract

SEVERAL authors^1,2 have suggested that synchrotron radiation by relativistic electrons in galactic magnetic fields may be responsible for part of the galactic background radiation at radio-frequencies. Radiation so produced is linearly polarized in a direction perpendicular to the magnetic field. The actual polarization observed from an extended region is likely to be reduced due to a number of mechanisms^3,4 which will be discussed elsewhere, but a small percentage might remain. Razin⁵ has described an attempt to measure this polarization by a method based on the suggestion that the Faraday effect in interstellar space would make the angular position of the plane of polarization strongly dependent upon frequency. By switching between a wide and a narrow receiver band-width, a change of output was noted which was interpreted as implying the presence of up to 4 per cent of linear polarization in some directions. On present evidence, the magnitude of the galactic magnetic field and of the electron density in interstellar space⁴ are thought insufficient for this dependence on frequency to lead to a reliable method of measurement, and a different procedure has been adopted. In the present method, a receiver band-width of 4 Mc./s. has been used, and although in certain circumstances the wider band-width might lead to a reduction of the polarization observed, the sensitivity is much improved, particularly when observing in directions away from the galactic plane.