High-velocity, asymmetric Doppler shifts of the X-ray emission lines of Cassiopeia A

Abstract

view Abstract Citations (68) References (35) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS High-velocity, asymmetric doppler shifts of the X-ray emission lines of Cassiopea A. Markert, T. H. ; Canizares, C. R. ; Clark, G. W. ; Winkler, P. F. Abstract Using the Focal Plane Crystal Spectrometer on the Einstein Observatory, we have performed high spectral resolution measurements of several X-ray emission lines from the young supernova remnant Cassiopeia A. The spectrum of the X-ray emitting gas in the northwest half of Cas A is redshifted with respect to that in the southeast. We interpret this phenomenon as a Doppler shift and find the mean velocity difference between the two regions to be 1820 ± 290 km s-1. Within each region the breadth of the X-ray lines implies a Doppler broadening of ∼5000km s-1 (FWHM). These measurements demonstrate directly that the bulk of the gas making up Cas A is moving at high velocities. We have constructed a simple geometric model consistent with the general features of the X-ray spectrum and image of Cas A-a broad ring of matter inclined to the line of sight. The data constrain the parameters of the model and in particular require an expansion velocity in excess of 2000 km s-1. The high velocities required for the X-ray matter (and the consequently high temperature of the primary shock) imply that the relatively cool X-ray emitting material that we observe is most probably supernova ejecta which has been heated by a reverse shock wave. Although alternative scenarios cannot be excluded, the X-ray and optical data are most compatible with the view that Cas A is still in its free-expansion stage. We find that the X-ray emitting mass is probably ≳10 Msun as previously determined by others, and the kinetic energy is ∼4 × 1051 ergs. The spatial and Doppler asymmetries may be caused by modest inhomogeneities either in the distribution of circumsource material or in the ejecta themselves, as has been suggested for rapidly rotating massive stars. Publication: The Astrophysical Journal Pub Date: May 1983 DOI: 10.1086/160939 Bibcode: 1983ApJ...268..134M Keywords: Cassiopeia A; Doppler Effect; Emission Spectra; Line Spectra; Supernova Remnants; X Ray Sources; Abundance; Astronomical Models; Astronomical Spectroscopy; High Resolution; High Speed; Red Shift; Spectral Line Width; Spectral Resolution; Stellar Mass Ejection; X Ray Spectra; Astrophysics full text sources ADS |