Bayesian insights in Tycho supernova remnant : a detailed mapping of ejecta properties

Abstract

While Tycho's supernova remnant is one of the most studied type Ia Galactic supernova remnants, a global view of the physical properties of its ejecta is lacking, to understand its mysteries. In particular, the spatial distribution of the Si-rich ejecta line-of-sight velocity presents a large-scale unexplained asymmetry, with the north dominantly blueshifted and the south redshifted. To investigate the origin of this line-of-sight velocity asymmetry in the ejecta, we carry out a detailed X-ray spatially-resolved spectral analysis of the entire shocked ejecta in Tycho's SNR to determine the physical properties of its various components. This study is based on the archival deep X-ray observations from the Chandra space telescope. The spatially-resolved spectral analysis in 211 regions over the entire SNR is based on a tesselation method applied to the line-of-sight velocity map. A Bayesian tool is used to conduct the fitting, using a nested sampling algorithm. It allows us to obtain a complete view of the statistical landscape. We provide maps of the physical parameters of the various components across the SNR ejecta. The Doppler shift map confirms spectrally the large-scale north-south asymmetry in the line-of-sight velocity. We reveal different spatial distributions of temperature and ionization time for IMEs and for iron-rich ejecta, but none of these maps shows structure associated to the large-scale north-south asymmetry in the line-of-sight velocity distribution. The abundance maps show spatial variations, depending on the element, perhaps due to an origin in different layers during the explosion. We compare these abundances with some nucleosynthesis models. In addition, we observe for the first time an emission line at 0.654 keV possibly related to oxygen. Its spatial distribution differs from the other elements, so that this line may arise in the ambient medium.