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27th of January 2022
An ORC near the LMC
by Filipovic et al.
Filipovic et al. report the discovery of J0624–6948, a low-surface brightness radio ring, lying between the Galactic Plane and the Large Magellanic Cloud (LMC), as illustrated above. Discovered at 888 MHz with the Australian Square Kilometre Array Pathfinder (ASKAP), the ring has a diameter of ∼196 arcsec. This source has phenomenological similarities to Odd Radio Circles (ORCs). However, significant differences to the known ORCs -- a flatter radio spectral index, the lack of a prominent central galaxy as a possible host, and larger apparent size -- suggest that J0624–6948 may be a different type of object. They argue that the most plausible explanation for J0624–6948 is an intergalactic supernova remnant due to a star that resided in the LMC outskirts that had undergone a single-degenerate type Ia supernova, and we are seeing its remnant expand into a rarefied, intergalactic environment. They also examine if a massive star or a white dwarf binary ejected from either galaxy could be the supernova progenitor. Finally, they consider several other hypotheses for the nature of the object, including the jets of an active galactic nucleus (AGN) or the remnant of a nearby stellar super-flare. The paper will be published in Monthly Notices of the Royal Astronomical Society.

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