The mass and energy budget of Cassiopeia A

¹ Department of Physics and Astronomy, University of Leicester, University Road, Leicester LE1 7RH, UK
² SRON National Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands e-mail: J.A.M.Bleeker@sron.nl; K.J.van.der.Heyden@sron.nl; j.s.kaastra@sron.nl

Corresponding author: R. Willingale, rw@star.le.ac.uk

Received: 11 July 2002
Accepted: 25 October 2002

Abstract

Further analysis of X-ray spectroscopy results (Willingale et al. 2002) recently obtained from the MOS CCD cameras on-board XMM-Newton provides a detailed description of the hot and cool X-ray emitting plasma in Cas A. Measurement of the Doppler broadening of the X-ray emission lines is consistent with the expected ion velocities, ~1500 km s^-1 along the line of sight, in the post shock plasma. Assuming a distance of 3.4 kpc, a constant total pressure throughout the remnant and combining the X-ray observations with optical measurements we estimate the total remnant mass as 10  and the total thermal energy as  J. We derive the differential mass distribution as a function of ionisation age for the hot and cool X-ray emitting components. This distribution is consistent with a hot component dominated by swept up mass heated by the primary shock and a cool component which are ablated clumpy ejecta material which were and are still being heated by interaction with the preheated swept up material. We calculate a balanced mass and energy budget for the supernova explosion giving a grand total of  J in an ejected mass; approximately ~0.4  of the ejecta were diffuse with an initial rms velocity ~ km s^-1 while the remaining ~1.8  were clumpy with an initial rms velocity of ~2400 km s^-1. Using the Doppler velocity measurements of the X-ray spectral lines we can project the mass into spherical coordinates about the remnant. This provides quantitative evidence for mass and energy beaming in the supernova explosion. The mass and energy occupy less than 4.5 sr (<40% of the available solid angle) around the remnant and 64% of the mass occurs in two jets within 45 degrees of a jet axis. We calculate a swept up mass of 7.9  in the emitting plasma and estimate that the total mass lost from the progenitor prior to the explosion could be as high as ~20 . We suggest that the progenitor was a Wolf-Rayet star that formed a dense nebular shell before the supernova explosion. This shell underwent heating by the primary shock which was energized by the fast diffuse ejecta.