Unexpected circular radio objects at high Galactic latitude

We have found a class of circular radio objects in the Evolutionary Map of the Universe Pilot Survey, using the Australian Square Kilometre Array Pathfinder telescope. The objects appear in radio images as circular edge-brightened discs, about one arcmin diameter, that are unlike other objects previously reported in the literature. We explore several possible mechanisms that might cause these objects, but none seems to be a compelling explanation.

Automated summary

A class of circular radio objects have been discovered in the Evolutionary Map of the Universe Pilot Survey, observed with the Australian Square Kilometre Array Pathfinder telescope. These objects appear as circular edge-brightened discs in radio images, with a diameter of about one arcmin, differing from previously reported objects. Various possible mechanisms for the formation of these objects have been explored, but none seem to provide a compelling explanation.