G107.5-1.5, a new SNR discovered through its highly polarized radio emission

A new highly polarized shell-type supernova remnant (SNR) has been discovered in the Canadian Galactic Plane Survey (CGPS). The only part of the remnant visible in radio continuum is a thin shell segment sitting on top of diffuse emission. The curvature of this segment indicates a much larger object which is not detectable in our observations most likely due to an imhomogenous ambient medium. A comparison of 408 MHz and 1420 MHz continuum emission reveals a spectral index of (alpha)=-0.6 ±0.1 (S~(nu)(alpha))), typical for a shell-type SNR. The polarized intensity averaged over the object is 50% of the total intensity, and the peak fractional polarization is close to the theoretical maximum, making this remnant the most highly polarized SNR known. At the projected centre of the radio shell is the unidentified X-ray point source 1RXS J225203.8+574249 which could be the neutron star left behind by the supernova explosion or its pulsar wind nebula. From the low rotation measure and possibly related HI features a distance of about 1.1 kpc is proposed. At this distance the radius of G107.5-1.5 is about 6 pc. The morphology and the structure of the ambient neutral hydrogen around the SNR suggests that this supernova remnant is in a late stage of evolution.