2014A&A...567A..59G

Large-scale radio continuum surveys have good potential for discovering new Galactic supernova remnants (SNRs). Surveys of the Galactic plane are often limited in the Galactic latitude of |b|∼5°. SNRs at high latitudes, such as the Cygnus Loop or CTA 1, cannot be detected by surveys in such limited latitudes. Using the available Urumqi λ6cm Galactic plane survey data, together with the maps from the extended ongoing λ6cm medium latitude survey, we wish to discover new SNRs in a large sky area. We searched for shell-like structures and calculated radio spectra using the Urumqi λ6cm, Effelsberg λ11cm, and λ21cm survey data. Radio polarized emission and evidence in other wavelengths are examined for the characteristics of SNRs. We discover an enclosed oval-shaped object G150.3+4.5 in the λ6cm survey map. It is about 2.°5 wide and 3° high. Parts of the shell structures can be identified well in the λ11cm, λ21cm, and λ73.5cm observations. The Effelsberg λ21cm total intensity image resembles most of the structures of G150.3+4.5 seen at λ6cm, but the loop is not closed in the northwest. High resolution images at λ21cm and λ73.5cm from the Canadian Galactic Plane Survey confirm the extended emission from the eastern and western shells of G150.3+4.5. We calculated the radio continuum spectral indices of the eastern and western shells, which are β~-2.4 and β~-2.7 between λ6cm and λ21cm, respectively. The shell-like structures and their non-thermal nature strongly suggest that G150.3+4.5 is a shell-type SNR. For other objects in the field of view, G151.4+3.0 and G151.2+2.6, we confirm that the shell-like structure G151.4+3.0 very likely has a SNR origin, while the circular-shaped G151.2+2.6 is an HII region with a flat radio spectrum associated with optical filamentary structure, Hα, and infrared emission.