Study of a giant Large Magellanic Cloud Supernova Remnant, Veliki (J0450.4-7050)

TL;DR

This study provides high-resolution radio and multi-frequency analysis of the Large Magellanic Cloud supernova remnant J0450.4-7050, revealing its large size, flat spectral index, and evidence of thermal and non-thermal emission components.

Contribution

It offers the first detailed high-resolution radio view of Veliki, revealing its extended size and complex emission characteristics, and proposes a new interpretation of its evolutionary state.

Findings

Veliki is one of the largest known SNRs in the LMC.

It exhibits a flat spectral index of -0.26, indicating a significant thermal emission component.

The remnant is likely an older, radiative SNR with a higher shock compression ratio.

Abstract

We present a high-resolution radio-continuum view and a multi-frequency analysis of the Large Magellanic Cloud (LMC) Supernova Remnant (SNR) J0450.4-7050, which we give the nickname Veliki. These high-resolution observations reveal a larger extent than previously measured, making J0450.4-7050 one of the largest SNRs that we know of. Additionally, we observe a higher than expected radio surface brightness and an unusually flat spectral index ($\alpha = -0.26 \pm 0.02$), with little spectral variation over the remnant. We observe a bright H$\alpha$ shell indicating significant cooling over the remnant, but also an excess of [Oiii] on the eastern shock front. We investigate several theoretical scenarios to explain the emission and radio evolution of J0450.4-7050 in the context of the LMC environment, and determine that this is most likely an older, predominantly radiative, SNR with a higher shock compression ratio, which gives a flatter non-thermal spectrum, in combination with a thermal (bremsstrahlung) emission contribution.