Determination of linear polarization and Faraday rotation of pulsar signals from spectral intensity modulation

Most of the known pulsars are sources of highly linearly polarized radiatio n. Faraday rotation in the intervening medium rotates the plane of the line ar polarization as the signals propagate through the medium. The Rotation M easure (RM), which quantifies the amount of such rotation as a function of wavelength, is useful in studying the properties of the medium and in recov ering the intrinsic polarization characteristics of the pulsar signal. Conv entional methods for polarization measurements use telescopes equipped with dual orthogonally polarized feeds that allow estimation of all 4 Stokes pa rameters. Some telescopes (such as the Ooty Radio Telescope) that offer hig h sensitivity for pulsar observations may however be receptive to only a si ngle linear polarization. In such a case, the apparent spectral intensity m odulation, resulting from differential Faraday rotation of the linearly pol arized signal component within the observing bandwidth, can be exploited to estimate the RM as well as to study the linear polarization properties of the source. In this paper, we present two improved procedures by which thes e observables can be estimated reliably from the intensity modulation over large bandwidths, particularly at low radio frequencies. We also highlight some other applications where such measurements and procedures would be use ful.