ROSAT PSPC observations of the remnant of SN 1006

Abstract

We report soft X-ray observations (∼0.1-2.4 keV) of the remnant of the AD 1006 supernova, obtained with the ROSAT PSPC in 1993 January. These data provide the best spectrally resolved X-ray images of the whole remnant yet recorded. The hard and soft components of the remnant known from previous observations are now very clearly defined. Analysis of the radial surface-brightness profiles demonstrates that the hard flux is confined to thin sheets located in two 'aegis' which cap the sides of the remnant at the north-east and south-west limbs. The interior flux is softer and is located in a shell which extends inwards to about 0.6 of the shock radius. The spectral analysis is characterized by two components, a thermal plasma and a power-law continuum. The power-law component is associated with the thin sheets which dominate in the aegis, and the thermal component comes from the interior. Apart from the aegis, the spatial distribution of X-ray-emitting material is approximately as expected from an isothermal Sedov model. We conclude that the remnant is at a distance of 0.7 ± 0.1 kpc, that the mass is 1.7 ± 0.7 M⊙, and that the thermal energy of the observed plasma is (2.4 ± 1.0) × 1049 erg. The ambient density is 0.40±0.06 cm-3, the mean shock radius is 3.6±0.5 pc, and the present shock velocity is (1.4±0.2) × 103 km s-1. The column density to the remnant is (3.9-5.7) × 1020 cm-2, yielding a mean density along the line of sight of 0.19-0.28 cm-3. It is likely that the thermal plasma is not in ionization equilibrium. We suggest that the aegis are formed by relativistic electrons, beamed from an otherwise unseen central object, interacting with the wound-up magnetic field in the post-shock region. The luminosity required from the central source is > 1.2 × 1034 erg s-1. The high velocity dispersion of the cold iron seen in absorption in the UV spectrum of the sbOB star (the so-called S-M star) near the centre of the remnant indicates that the bulk of this material must be outside the shock radius. The estimated kinetic energy in this cold halo is 2 × 1049 erg, so the total initial energy of the supernova was > 4.4 × 1049 erg.