Mysterious Odd Radio Circle near the Large Magellanic Cloud -- An Intergalactic Supernova Remnant?

TL;DR

The paper reports the discovery of a peculiar radio ring near the LMC, likely an intergalactic supernova remnant from a Type Ia supernova, with unique features distinguishing it from known ORCs.

Contribution

It introduces J0624-6948 as a new type of intergalactic supernova remnant, expanding understanding of supernova remnants in intergalactic space.

Findings

J0624-6948 is a low-surface brightness radio ring with a diameter of ~196 arcsec.

It has a flatter spectral index and lacks a central galaxy compared to known ORCs.

The most plausible origin is a Type Ia supernova remnant from an LMC star.

Abstract

We report the discovery of J0624-6948, a low-surface brightness radio ring, lying between the Galactic Plane and the Large Magellanic Cloud (LMC). It was first detected at 888 MHz with the Australian Square Kilometre Array Pathfinder (ASKAP), and with a diameter of ~196 arcsec. This source has phenomenological similarities to Odd Radio Circles (ORCs). 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. We 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. We also examine if a massive star or a white dwarf binary ejected from either galaxy could be the supernova progenitor. Finally, we 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.