Bayesian insights into the Tycho supernova remnant: A detailed mapping of ejecta properties

¹ Université Paris Cité, Université Paris-Saclay, CEA, CNRS, AIM, 91191 Gif-sur-Yvette, France
² Université Paris-Saclay, Université Paris Cité, CEA, CNRS, AIM, 91191 Gif-sur-Yvette, France
³ FSLAC IRL 2009, CNRS/IAC, La Laguna, Tenerife, Spain

^★ Corresponding authors; leila.godinaud@cea.fr, fabio.acero@cea.fr

Received: 26 April 2024
Accepted: 22 November 2024

Abstract

Context. While Tycho’s supernova remnant (SNR) is one of the most studied type Ia Galactic SNRs, a global view of the physical properties of its ejecta is lacking to be able to understand its mysteries. In particular, the spatial distribution of the Si-rich ejecta line- of-sight velocity presents a unexplained large-scale asymmetry, with the north dominantly blueshifted and the south redshifted.

Aims. To investigate the origin of this line-of-sight velocity asymmetry in the ejecta and its current dynamics, we carried 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.

Methods. The spatially resolved spectral analysis in 211 regions over the entire SNR is based on a tessellation method applied to the line-of-sight velocity map. We modelled the ejecta emission with two thermal non-equilibrium ionisation components of different compositions for intermediate-mass elements (IME) and iron-rich ejecta. We included Doppler shift and line broadening and added a power law for the synchrotron emission, and additional constraints. A Bayesian tool was used to conduct the fitting, using a nested sampling algorithm. This allowed us to us to obtain a complete view of the statistical landscape.

Results. We provide maps of the physical parameters of the various components across the SNR ejecta. The Doppler shift map spectrally confirms the large-scale north-south asymmetry in the line-of-sight velocity that was obtained from a general morphological component analysis. We reveal different spatial distributions of temperature and ionisation time for IMEs and for iron-rich ejecta, but none of these maps shows a structure associated with the large-scale north-south asymmetry in the line-of-sight velocity distribution. In the IME component, we observed an overall anti-correlation between the temperature and ionisation time that could arise from different ionisation histories. 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 this line may arise in the ambient medium.