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SummaryThe results of a study of Centaurus A in the wavelength range 6-74 cm are presented. From observations at 11, 21, and 31 cm the intrinsic polarization and Faraday rotation have been determined for much of the source.Of the two sources that form the central component, the north-following source is strongly polarized at wavelengths shorter than about 31 cm. The southpreceding source is 3% polarized at 6 cm and not more than 3% polarized at 11 cm.At 11 and 21 cm the degree of polarization in extended regions of the source is typically 10-20% and in places as high as 40%. The orientation of the intrinsic polarization is quite uniform over large areas but appears to bear no constant relationship to the axis of symmetry of the source.In general the rotation measure varies slowly over the source, and values lie in the range -36 to -84 rad/m2, with most values lying between -'-50 and -70 rad/m2• Possible relationships between Faraday rotation and depolarization effects are discussed.All parts of the source have an essentially constant spectral index of -0·6 at decimetric wavelengths. The central component contributes approximately 22% of the total flux density, the remainder being equally divided between the northern and southern extended sources.

Context. New and existing large-scale radio surveys of the Milky Way at centimetre wavelengths can play an important role in uncovering the hundreds of expected but missing supernova remnants in the Galaxy's interstellar medium. We report on the discovery of two supernova remnants (SNRs) designated G152.4−2.1 and G190.9−2.2, using Canadian Galactic Plane Survey data. Aims. The aims of this paper are, first, to present evidence that favours the classification of both sources as SNRs, and, second, to describe basic parameters (integrated flux density, spectrum, and polarization) as well as properties (morphology, line-of-sight velocity, distance and physical size) to facilitate and motivate future observations. Methods. Spectral and polarization parameters are derived from multiwavelength data from existing radio surveys carried out at wavelengths between 6 and 92 cm. In particular for the source G152.4−2.1 we also use new observations at 11 cm done with the Effelsberg 100 m telescope. The interstellar medium around the discovered sources is analyzed using 1-arcmin line data from neutral hydrogen (H i) and 45-arcsec 12 CO(J = 1 → 0).Results. G152.4−2.1 is a barrel shaped SNR with two opposed radio-bright polarized flanks on the north and south. The remnant, which is elongated along the Galactic plane is evolving in a more-or-less uniform medium. G190.9−2.2 is also a shell-type remnant with east and west halves elongated perpendicular to the plane, and is evolving within a low-density region bounded by dense neutral hydrogen in the north and south, and molecular ( 12 CO) clouds in the east and west. The integrated radio continuum spectral indices are −0.65 ± 0.05 and −0.66 ± 0.05 for G152.4−2.1 and G190.9−2.2 respectively. Both SNRs are approximately 1 kpc distant, with G152.4−2.1 being larger (32 × 30 pc in diameter) than G190.9−2.2 (18 × 16 pc). These two remnants are the lowest surface brightness SNRs yet catalogued at Σ 1 GHz < ∼ 5 × 10 −23 W m −2 Hz −1 sr −1 .

Circular polarization measurements were made with the Parkes 64 m telescope on 66 mainly extragalactic sources, 33 of which were studied at two or more frequencies. Circular polarization was definitely found in the eight quasi-stellar sources PKS0237-23, 0537-441, 1127-14, 1226+02 (3C273), 1253-05 (3C279), 2134+004, 2145+06 and 2345-16, as it was measured at the 4u level or higher in at least two observing sessions. For all eight sources the total power spectrum shows the effects of self~absorption. For none of the eight is there evidence of a reversal of the sense of polarization with frequency. 'For several of the sources the degree of circular polarization changed by a factor ~ 2 between observing sessions, while any accompanying change in total flux density was ;S 20 %. Instrumental effects are discussed in some detail. Fluctuations due to system noise provide the main limitation, but for strong sources uncertainties in the determination of the zero of polarization are important.