XMM-Newton observations of SNR 1987A. II. The still increasing X-ray light curve and the properties of Fe K lines

Abstract

Aims: We report on the recent observations of the supernova remnant SNR 1987A in the Large Magellanic Cloud with XMM-Newton. Carefully monitoring the evolution of the X-ray light curve allows us to probe the complex circumstellar medium structure observed around the supernova progenitor star.
Methods: We analysed all XMM-Newton observations of SNR 1987A from January 2007 to December 2011, using data from the EPIC-pn camera. Spectra from all epochs were extracted and analysed in a homogeneous way. Using a multi-shock model to fit the spectra across the 0.2-10 keV bandm we measured soft and hard X-ray fluxes with high accuracy. In the hard X-ray band we examined the presence and properties of Fe K lines. Our findings have been interpreted in the framework of a hydrodynamics-based model.
Results: The soft X-ray flux of SNR 1987A has continuously increased in recent years. Although the light curve shows a mild flattening, there is no sudden break as reported in an earlier work, a picture echoed by a revision of the Chandra light curve. We therefore conclude that material in the equatorial ring and out-of-plane H ii regions are still being swept up. We estimate the thickness of the equatorial ring to be at least 4.5 × 10¹⁶ cm (0.0146 pc). This lower limit will increase as long as the soft X-ray flux has not reached a turn-over. We detect a broad Fe K line in all spectra from 2007 to 2011. The widths and centroid energies of the lines indicate there is a collection of iron ionisation stages. Thermal emission from the hydrodynamic model does not reproduce the low-energy part of the line (6.4-6.5 keV), suggesting that fluorescence from neutral and/or low ionisation Fe might be present.

Based on observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA.