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 degree. 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 6 cm Galactic plane survey data, together with the maps from the extended ongoing 6 cm 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 6 cm, Effelsberg 11 cm, and 21 cm survey data. Radio polarized emission and evidence in other wavelengths are also examined for the characteristics of SNRs. We discover an enclosed oval-shaped object G150.3+4.5 in the 6 cm survey map. It is about 2.5 degree wide and 3 degree high. Parts of the shell structures can be identified well in the 11 cm, 21 cm, and 73.5 cm observations. The Effelsberg 21 cm total intensity image resembles most of the structures of G150.3+4.5 seen at 6 cm, but the loop is not closed in the northwest. High resolution images at 21 cm and 73.5 cm 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 $β\sim -2.4$ and $β\sim -2.7$ between 6 cm and 21 cm, 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, H$α$, and infrared emission.
Odd Radio Circles as supernovae remnants in the intragroup medium
在最近发现的弧分大小的圆形弥散射电源中，有一部分（$\sim8$ %）被称为奇射电圈（Odd Radio Circles）或ORC，它们可能是本星系群及其近邻星系群内群内介质中的超新星遗迹。这一估计是基于光学探测率的群内超新星事件在附近（$z \sim 0.1-0.2$）星系群。在本星系群及其邻近的星系群中，预计每百万年约有5400颗群内超新星。对于一个约为$10^{4}$年的射电可探测周期，平均每1000平方度1.3个群内中等超新星遗迹预计将在射电勘测中被探测到，其灵敏度导致了ORC的发现。在群内介质中，距离$\sim3$ Mpc的超新星遗迹的角大小、表面亮度和射电通量可以预期与五个已知的ORC相似。群内超新星遗迹并不存在于星系的致密和寒冷的星际介质中，而是在星系晕或更远的低密度（$10^{-4}-10^{-5}$ cm $^{-3}$）温暖介质（$10^{5}-10^{6}$ K）中演化，并且可能在与银河系和其他附近星系周围的各种潮汐流光相关的漫射恒星光中找到它们的祖先。
