Stingrays in the radio sky: Two unusual diffuse radio relic sources in the direction of the Magellanic Stream

TL;DR

This paper reports the discovery of two unusual diffuse radio sources near the Magellanic Stream, analyzing their properties and exploring various possible origins, with the most likely being head-tail radio galaxies, though their exact nature remains uncertain.

Contribution

First detailed radio continuum analysis of two diffuse sources near the Magellanic Stream, combining ASKAP and GLEAM data to explore their origins.

Findings

Sources exhibit non-thermal emission with distinct spectral indices.

Multiple scenarios considered, but none fully explain the observed properties.

Most likely they are complex environmental interactions, possibly head-tail radio galaxies.

Abstract

We present the discovery of two extended, low surface brightness radio continuum sources, each consisting of a near-circular body and an extended tail of emission, nicknamed Stingray 1 (ASKAP J0129-5350) and Stingray 2 (ASKAP J0245-5642). Both are found in the direction of the Magellanic Stream (MS) and were discovered in the Australian Square Kilometre Array Pathfinder (ASKAP) Evolutionary Map of the Universe (EMU) survey at 944 MHz. We combine the ASKAP data with low-frequency radio observations from the GaLactic and Extragalactic All-sky MWA Survey (GLEAM) to conduct a radio continuum analysis. We explore both Galactic/near Galactic scenarios, including runaway or circumgalactic supernova remnants (SNRs) and parentless pulsar-wind nebulae (PWNe), and extragalactic scenarios including radio active galactic nuclei (AGNs), dying radio galaxies, galaxy clusters, galaxy pairs or groups, head-tail radio galaxies, and Odd Radio Circles (ORCs), as well as the possibility that the morphology is due to a chance alignment. The Stingrays exhibit non-thermal emission with spectral indices of $\alpha$ = -0.89 $\pm$ 0.09 for Stingray 1 and $\alpha$ = -1.77 $\pm$ 0.06 for Stingray 2. We find that none of the proposed scenarios can explain all of the observed properties, however we determine it most likely that their shape is caused by some kind of complex environmental interaction. The most likely scenario from the available data is that of a head-tail radio galaxy, but more data is required for a definitive classification.