Paper detail

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

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.