POLARIZATION OF COSMIC X‐RAY SOURCES *

The x-ray polarimeters on the OSO-8 satellite are being used for a systematic study of the polarization of a number of cosmic x-ray sources. Such observations, together with studies of the energy spectra and time variability, provide important information in identifying and understanding the underlying x-ray emission mechanisms. The role of polarimetry in x-ray astronomy was established by the discovery of x-ray polarization in the Crab Nebula,' where the magnitude and position angle of the x-ray polarization were found to be similar to those observed in the optical region of the spectrum. This result, together with the observed powerlaw spectrum and the discovery of the pulsar as the source of energy, showed that the x-rays are produced by the synchrotron process. Our current understanding of other x-ray sources, such as binary systems and radio galaxies, indicates that the x-ray emission processes may give rise to substantial amounts of polarization.2 In this paper we briefly review the theory and design of the OSO-8 polarimeters. We give new precise values for the polarization of the Crab Nebula a t 2.6 and 5.2 keV, and we give preliminary values for the polarization of the Crab pulsar, Cyg X-I , and Cyg X-2 at 2.6 keV.