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

Filipović MD, Smeaton ZJ, Kothes R, Mantovanini S, Kostić P, Leahy D, Ahmad A, Anderson G, Araya M, Ball BD, Becker W, Bordiu C, Bradley AC, Brose R, Burger-Scheidlin C, Dai S, Duchesne S, Galvin TJ, Hopkins AM, Hurley-Walker N, Koribalski BS, Lazarević S, Lundqvist P, Mackey J, Martin P, McGee P, Mitrašinović A, Payne JL, Riggi S, Ross K, Rowell G, Rudnick L, Sano H, Sasaki M, Roberto S, Urošević D, Vukotić B, West J (2025)

Publication Type: Journal article

Publication year: 2025

Journal

Book Volume: 42

Article Number: e104

DOI: 10.1017/pasa.2025.10045

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"x1 260" and PA = 0°. While there is a hint of possible H(Formula presented) 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 (Formula presented)=-0.6(Formula presented)0.3. Our best estimates from Hi studies and the (Formula presented)-D relation place Teleios as a type Ia SNR at a distance of either (Formula presented)2.2 kpc (near-side) or (Formula presented)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 (Formula presented)1 kpc and Teleios size of only (Formula presented)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.

Authors with CRIS profile

Involved external institutions

University of Western Sydney Australia (AU) National Research Council / Conseil national de recherches Canada Canada (CA) International Centre for Radio Astronomy Research Australia (AU) Astronomical Observatory Belgrade Serbia (RS) University of Calgary Canada (CA) Universidad de Costa Rica Costa Rica (CR) University of Alberta Canada (CA) Max-Planck-Institut für extraterrestrische Physik (MPE) / Max Planck Institute for Extraterrestrial Physics Germany (DE) National Institute for Astrophysics / Istituto Nazionale Astrofisica (INAF) Italy (IT) Dublin City University (DCU) Ireland (IE) DIAS Dunsink Observatory Ireland (IE) University of Minnesota (UMN) United States (USA) (US) Commonwealth Scientific and Industrial Research Organisation (CSIRO) Australia (AU) Gifu University / 岐阜大学 Japan (JP) University of Belgrade / Универзитет у Београду Serbia (RS) Macquarie University Australia (AU) The Oskar Klein Centre Sweden (SE) Institut de Recherche en Astrophysique et Planétologie (IRAP) France (FR) University of Adelaide Australia (AU)

How to cite

APA:

Filipović, M.D., Smeaton, Z.J., Kothes, R., Mantovanini, S., Kostić, P., Leahy, D.,... West, J. (2025). Teleios (G305.4-2.2) - the mystery of a perfectly shaped new galactic supernova remnant. Publications of the Astronomical Society of Australia, 42. https://doi.org/10.1017/pasa.2025.10045

MLA:

Filipović, Miroslav D., et al. "Teleios (G305.4-2.2) - the mystery of a perfectly shaped new galactic supernova remnant." Publications of the Astronomical Society of Australia 42 (2025).

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