2023A&A...680A..80G

Context. Even 450 yr after the explosion of the Type Ia SN 1572, the dynamics of the Tycho supernova remnant (Tycho's SNR) can offer keys to improving our understanding of the explosion mechanism and the interaction of the remnant with the interstellar medium.
Aims. To probe the asymmetries and the evolution of the SNR, we tracked the ejecta dynamics using new methods applied to the deep X-ray observations available in the Chandra space telescope archive.
Methods. For the line-of-sight (LoS) velocity measurement (V_z), we used the Doppler effect focused on the bright Si line in the 1.6-2.1 keV band. Using the component separation tool called general morphological component analysis (GMCA), we successfully disentangled the red and blueshifted Si ejecta emission. This allowed us to reconstruct a map of the peak energy of the silicon line with a total coverage of the SNR at a 2″ resolution. We then obtained a proxy of the integrated velocity along the LoS. For the proper motions in the plane of the sky (V_xy), we developed a new method, called Poisson optical flow (POF), to measure the displacement of two-dimensional (2D) features between the observations of 2003 and 2009. The result is a field of around 1700 velocity vectors covering the entire SNR.
Results. These exhaustive three-dimensional (3D) velocity measurements reveal the complex dynamics of Tycho's SNR. Our study sheds light on a patchy V_z map, where most regions are dominated by the foreground or the background part of the shell. On a large scale, an asymmetry is seen, with the north being dominantly blueshifted and the south redshifted. The proper-motion vector field, V_xy, highlights different dynamics between the eastern and the western parts of the SNR. The eastern velocity field is more disturbed by external inhomogeneities and the south-east ejecta knot. In particular, a slow-down is observed in the north-east, which could be due to the interaction with higher densities, as seen in other wavelengths. The vector field is also used to backtrace the center of the explosion, which is then compared with potential stellar progenitors in the area. The latest Gaia DR3 parallax measurements exclude most stellar candidates based on their distances, leaving only stars B and E as possible candidates, at respective distances of 2.53_–0.20^+0.23 kpc and 3.52_–1.0^+2.0 kpc, which are consistent with the expected distance range of the SNR at 2.5-4 kpc.