Two Radio Supernova Remnants Discovered in the Outer Galaxy

Abstract: 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. 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. Spectral and polarization parameters are derived from multiwavelength data from existing radio surveys carried out at wavelengths between 6 and 92cm. In particular for the source G152.4-2.1 we also use new observations at 11cm done with the Effelsberg 100m telescope. The interstellar medium around the discovered sources is analyzed using 1-arcminute line data from neutral hydrogen (HI) and 45-arcsecond 12CO(J=1-0). 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 (12CO) 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 (32x30 pc in diameter) than G190.9-2.2 (18x16 pc). These two remnants are the lowest surface brightness SNRs yet catalogued at 5x10^-23 W m^-2 Hz^-1 sr^-1.