Evidence for Resonance Scattering in the X-Ray Grating Spectrum of the Supernova Remnant N49

Resonance scattering (RS) is an important process in astronomical objects, because it affects measurements of elemental abundances and distorts surface brightness of the object. It is predicted that RS can occur in plasmas of supernova remnants (SNRs). Although several authors reported hints of RS in SNRs, no strong observational evidence has been established so far. We perform a high-resolution X-ray spectroscopy of the SNR N49 with the Reflection Grating Spectrometer on board XMM-Newton. The Reflection Grating Spectrometer spectrum of N49 shows a high G-ratio of O VII Heα lines as well as O VIII Lyβ/α and Fe XVII (3s-2p)/(3d-2p) ratios, which cannot be explained by the emission from a thin thermal plasma. These line ratios can be well explained by the effect of RS. Our result implies that RS has a large impact particularly on a measurement of the oxygen abundance.