[Paper Review] Multi-frequency study of Local Group Supernova Remnants The curious case of the Large Magellanic Cloud SNR J0528-6714

E. J. Crawford, M. D. Filipović+4 more|Max Planck Digital Library|Jun 2, 2010

Astrophysical Phenomena and Observations32 references10 citations

TL;DR

This study investigates the unusual Large Magellanic Cloud supernova remnant SNR J0528–6714, which exhibits strong radio emission but lacks optical and faint X-ray counterparts. Using multi-frequency ATCA, XMM-Newton, and MCELS observations, the authors confirm it as a mature, older SNR with a radio spectral index of −0.36 ± 0.09, circular morphology, and non-equilibrium ionisation X-ray plasma at kT = 0.26 keV, indicating a Type Ia origin and advanced evolutionary stage.

ABSTRACT

Aims. Recent ATCA, XMM-Newton and MCELS observations of the Magellanic Clouds (MCs) cover a number of new and known SNRs which are poorly studied, such as SNR J0528-6714 . This particular SNR exhibits luminous radio-continuum emission, but is one of the unusual and rare cases without detectable optical and very faint X-ray emission (initially detected by ROSAT and listed as object [HP99] 498). We used new multi-frequency radio-continuum surveys and new optical observations at Hα, [S ii] and [O iii] wavelengths, in combination with XMM-Newton X-ray data, to investigate the SNR properties and to search for a physical explanation for the unusual appearance of this SNR. Methods. We analysed the X-ray and Radio-Continuum spectra and present multi-wavelength morphological studies of this SNR. Results. We present the results of new moderate resolution ATCA observations of SNR J0528-6714. We found that this object is a typical older SNR with a radio spectral index of α=-0.36 \pm 0.09 and a diameter of D=52.4 \pm 1.0 pc. Regions of moderate and somewhat irregular polarisation were detected which are also indicative of an older SNR. Using a non-equilibrium ionisation collisional plasma model to describe the X-ray spectrum, we find temperatures kT of 0.26 keV for the remnant. The low temperature, low surface brightness, and large extent of the remnant all indicate a relatively advanced age. The near circular morphology indicates a Type Ia event. Conclusions. Our study revealed one of the most unusual cases of SNRs in the Local Group of galaxies - a luminous radio SNR without optical counterpart and, at the same time, very faint X-ray emission. While it is not unusual to not detect an SNR in the optical, the combination of faint X-ray and no optical detection makes this SNR very unique.

Motivation & Objective

• To resolve the physical nature of SNR J0528–6714, a luminous radio SNR in the Large Magellanic Cloud with no detectable optical or strong X-ray emission.
• To investigate the cause of its unusual multi-wavelength appearance, particularly the absence of optical and weak X-ray signatures despite strong radio emission.
• To determine the age, morphology, and progenitor type of the remnant using multi-wavelength data.
• To assess whether the remnant is consistent with a Type Ia supernova explosion and adiabatic phase evolution.
• To evaluate the possibility of alternative explanations such as a pulsar wind nebula or line-of-sight obscuration.

Proposed method

• Conducted new moderate-resolution ATCA observations at 6 cm (4790 MHz) and 3 cm (8640 MHz) to map radio-continuum emission and derive the radio spectral index.
• Analyzed archival XMM-Newton EPIC-PN and MOS data (0.2–4.5 keV) to extract X-ray spectra and model the plasma using a non-equilibrium ionisation (NEI) model.
• Performed multi-wavelength morphological comparisons by overlaying ATCA 6 cm radio contours with MCELS Hα, [S ii], and [O iii] optical emission-line images.
• Measured the remnant’s diameter (52.4 ± 1.0 pc) and assessed polarization features to infer magnetic field structure and evolutionary stage.
• Used the radio spectral index and X-ray temperature to estimate the remnant’s age and evolutionary phase.
• Evaluated the spatial offset between the radio peak and a central X-ray point source to rule out pulsar wind nebula (PWN) origin.

Experimental results

Research questions

• RQ1 Why does SNR J0528–6714 exhibit strong radio emission but no detectable optical or X-ray emission?
• RQ2 What is the evolutionary stage of this SNR, and does its morphology and spectral properties support a Type Ia supernova origin?
• RQ3 Could the lack of optical and faint X-ray emission be due to line-of-sight obscuration or intrinsic physical conditions?
• RQ4 Is the central X-ray point source associated with the remnant, and does it support a Pulsar Wind Nebula (PWN) interpretation?
• RQ5 How do the polarization features and spectral index inform the remnant’s age and magnetic field evolution?

Key findings

• SNR J0528–6714 has a diameter of 52.4 ± 1.0 pc, placing it among the larger known SNRs in the LMC.
• The radio spectral index α = –0.36 ± 0.09 indicates a mature, older SNR in the adiabatic phase of evolution.
• Moderate and irregular polarisation features (up to 15% fractional polarisation) support an aged remnant with a weakened magnetic field.
• XMM-Newton X-ray data reveal a low-temperature plasma with kT = 0.26 keV, best fit by a non-equilibrium ionisation (NEI) model.
• The remnant shows no significant optical emission in Hα, [S ii], or [O iii] bands, confirming the absence of a detectable optical counterpart.
• The near-circular morphology and lack of radial asymmetry strongly suggest a Type Ia supernova origin, consistent with a single-degenerate progenitor system.