Teleios (G305.4–2.2) – the mystery of a perfectly shaped new galactic supernova remnant

Abstract We present the serendipitous radio-continuum discovery of a likely Galactic supernova remnant (SNR) G305.4–2.2. This object displays a remarkable circular symmetry in shape, making it one of the most circular Galactic SNRs known. Nicknamed Teleios due to its symmetry, it was detected in the new Australian Square Kilometre Array Pathfinder (ASKAP) Evolutionary Map of the Universe (EMU) radio–continuum images with an angular size of 1 320 $^{\prime\prime}$ $\times$ 1 260 $^{\prime\prime}$ and PA = 0 $^\circ$ . While there is a hint of possible H $\alpha$ and gamma-ray emission, Teleios is exclusively seen at radio–continuum frequencies. Interestingly, Teleios is not only almost perfectly symmetric, but it also has one of the lowest surface brightnesses discovered among Galactic SNRs and a steep spectral index of $\alpha$ =–0.6 $\pm$ 0.3. Our best estimates from H i studies and the $\Sigma$ –D relation place Teleios as a type Ia SNR at a distance of either $\sim$ 2.2 kpc (near-side) or $\sim$ 7.7 kpc (far-side). This indicates two possible scenarios, either a young (under 1 000 yr) or a somewhat older SNR (over 10 000 yr). With a corresponding diameter of 14/48 pc, our evolutionary studies place Teleios at the either early or late Sedov phase, depending on the distance/diameter estimate. However, our modelling also predicts X-ray emission, which we do not see in the present generation of eROSITA images. We also explored a type Iax explosion scenario that would point to a much closer distance of $\lt$ 1 kpc and Teleios size of only $\sim$ 3.3 pc, which would be similar to the only known type Iax remnant SN1181. Unfortunately, all examined scenarios have their challenges, and no definitive Supernova (SN) origin type can be established at this stage. Remarkably, Teleios has retained its symmetrical shape as it aged even to such a diameter, suggesting expansion into a rarefied and isotropic ambient medium. The low radio surface brightness and the lack of pronounced polarisation can be explained by a high level of ambient rotation measure (RM), with the largest RM being observed at Teleios’s centre.

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Journal
Publications of the Astronomical Society of Australia
Published
2025-01-01
DOI
https://doi.org/10.1017/pasa.2025.10045
Citations
1
Primary Topic
Astrophysics and Cosmic Phenomena
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article
Field-Weighted Citation Impact
1.87
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article

Teleios (G305.4–2.2) – the mystery of a perfectly shaped new galactic supernova remnant

B. Ball, S. W. Duchesne, Miguel Araya, Sanja Lazarević et al.
1 citations
Publications of the Astronomical Society of Australia
Astrophysics and Cosmic Phenomena
1.87
article

Teleios (G305.4–2.2) – the mystery of a perfectly shaped new galactic supernova remnant

B. Ball, S. W. Duchesne, Miguel Araya, Sanja Lazarević, Gavin Rowell, Andrew Hopkins, Miroslav D Filipović, Roberto Soria, S. Riggi, Hidetoshi Sano, G. E. Anderson, J. L. Payne, Robert Brose, L. Rudnick, Adeel Ahmad, Kathryn Ross, P. McGee, Jonathan Mackey, Petar Kostić, N. Hurley‐Walker, Peter Lundqvist, R. Kothes, Jennifer West, Branislav Vukotić, C. Burger-Scheidlin, Timothy J. Galvin, D. A. Leahy, M. Sasaki, Cristóbal Bordiú, Ana Mitrašinović, Andy Bradley, W. Becker, Shi Dai, D. Urošević, B. Koribalski, Silvia Mantovanini, Zachary J. Smeaton, Pierrick Martin
article en
1 citations

Abstract

Abstract We present the serendipitous radio-continuum discovery of a likely Galactic supernova remnant (SNR) G305.4–2.2. This object displays a remarkable circular symmetry in shape, making it one of the most circular Galactic SNRs known. Nicknamed Teleios due to its symmetry, it was detected in the new Australian Square Kilometre Array Pathfinder (ASKAP) Evolutionary Map of the Universe (EMU) radio–continuum images with an angular size of 1 320 $^{\prime\prime}$ $\times$ 1 260 $^{\prime\prime}$ and PA = 0 $^\circ$ . While there is a hint of possible H $\alpha$ and gamma-ray emission, Teleios is exclusively seen at radio–continuum frequencies. Interestingly, Teleios is not only almost perfectly symmetric, but it also has one of the lowest surface brightnesses discovered among Galactic SNRs and a steep spectral index of $\alpha$ =–0.6 $\pm$ 0.3. Our best estimates from H i studies and the $\Sigma$ –D relation place Teleios as a type Ia SNR at a distance of either $\sim$ 2.2 kpc (near-side) or $\sim$ 7.7 kpc (far-side). This indicates two possible scenarios, either a young (under 1 000 yr) or a somewhat older SNR (over 10 000 yr). With a corresponding diameter of 14/48 pc, our evolutionary studies place Teleios at the either early or late Sedov phase, depending on the distance/diameter estimate. However, our modelling also predicts X-ray emission, which we do not see in the present generation of eROSITA images. We also explored a type Iax explosion scenario that would point to a much closer distance of $\lt$ 1 kpc and Teleios size of only $\sim$ 3.3 pc, which would be similar to the only known type Iax remnant SN1181. Unfortunately, all examined scenarios have their challenges, and no definitive Supernova (SN) origin type can be established at this stage. Remarkably, Teleios has retained its symmetrical shape as it aged even to such a diameter, suggesting expansion into a rarefied and isotropic ambient medium. The low radio surface brightness and the lack of pronounced polarisation can be explained by a high level of ambient rotation measure (RM), with the largest RM being observed at Teleios’s centre.

Publications of the Astronomical Society of AustraliaVol. 42
University College Dublin (IE), Herzberg Institute of Astrophysics (CA), Commonwealth Scientific and Industrial Research Organisation (AU), Centre National de la Recherche Scientifique (FR), The University of Sydney (AU), Australia Telescope National Facility (AU), University of Minnesota (US), Dublin Institute For Advanced Studies (IE), University of Alberta (CA), Stockholm University (SE), University of Calgary (CA), University of Potsdam (DE), Université Fédérale de Toulouse Midi-Pyrénées (FR), Friedrich-Alexander-Universität Erlangen-Nürnberg (DE), Curtin University (AU), Dominion Astrophysical Observatory (CA), Regional Medical Research Centre (IN), Universidad de Costa Rica (CR), University of Belgrade (RS), Max Planck Institute for Extraterrestrial Physics (DE), Osservatorio Astrofisico di Torino (IT), EarthTech International (United States) (US), Osservatorio Astrofisico di Catania (IT), Astronomical Observatory (RS), Max Planck Institute for Radio Astronomy (DE), National Astronomical Observatory of Japan (JP), Gifu University (JP), Dublin City University (IE), The University of Adelaide (AU), Western Sydney University (AU), Macquarie University (AU)
Openalex Percentile: Top 12%
Astrophysics and Cosmic Phenomena
1.87
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