High-Resolution X-Ray Spectroscopy of Galactic Supernova Remnants

Satoru Katsuda,Hiroshi Tsunemi

doi:10.14311/app.2014.01.0200

Abstract

High-resolution X-ray spectroscopy of Galactic supernova remnants (SNRs), based on grating spectrometers onboard XMM-Newton and Chandra, has been revealing a variety of new astrophysical phenomena. Broadened oxygen lines for a northwestern compact knot in SN 1006 clearly show a high oxygen temperature of ~300 keV. The high temperature together with a lower electron temperature (kTe ~ 1 keV) can be reasonably interpreted as temperature non-equilibration between electrons and oxygen behind a collisionless shock. An ejecta knot in the Puppis A SNR shows blueshifted line emission by ~ 1500kms-1. The line widths are fairly narrow in contrast to the SN 1006's knot; an upper limit of 0.9 eV is obtained for O VIII Lyα, which translates to an oxygen temperature of kTO &lt; 30 keV. The low temperature suggests that the knot was heated by a reverse shock whose velocity is 4 times slower than that of a forward shock. Anomalous intensity ratios in O VII Heα lines, i.e., a stronger forbidden line than a resonance line, is found in a cloud-shock interaction region in Puppis A. The line ratio can be best explained by the charge-exchange emission that should arise at interfaces between the cold/warm clouds and the hot plasma. There are several other targets for which we plan to analyze high-quality grating data prior to the operation of the soft X-ray spectrometer onboard Astro-H.

Highlights

There are many scientific motivations to perform highresolution X-ray spectroscopy of supernova remnants (SNRs), since the X-ray emission is often dominated by thin thermal emission, namely line emission
While they work well for point-like sources or compact extended sources, they are generally not suitable for largely extended sources because off-axis emission along the dispersion direction is detected at wavelength positions shifted with respect to the on-axis source
Most SNRs in the large/small Magellanic clouds are small enough for the gratings, and over 10 papers have been published in literature (e.g., Burrows et al 2000; Rasmussen et al 2001; Behar et al 2001; van der Heyden et al 2001; 2002; 2003; Flanagan et al 2004; Kosenko et al 2008; 2011; Broersen et al 2011)

Summary

Introduction

There are many scientific motivations to perform highresolution X-ray spectroscopy of supernova remnants (SNRs), since the X-ray emission is often dominated by thin thermal emission, namely line emission. Current challenges are based on grating spectrometers onboard XMM-Newton and Chandra. Both of the grating systems are slitless. A problem here is that we can not deduce spatial information, since the grating spectra are integrated for the entire SNR. It is important to observe large Galactic SNRs for spatiallyresolved high-resolution spectroscopy. In this case, grating spectra suffer from spectral degradation due to the spatial extent of the source. The only solution to this dilemma is to focus on locally bright and compact features in large SNRs. We here review a few successful examples of high-resolution spectroscopy of Galactic SNRs with the XMM-Newton’s reflection grating spectrometer (RGS: den Herder et al 2001). The RGS has a large dispersion angle and is more suitable for extended sources than Chandra’s grating spectrometer, there are some nice results (Lazendic et al 2006; Rutherford et al 2013)

Fast-Moving Knots in SN 1006 and Puppis A

Cloud-Shock Interaction Regions in Puppis A