John

Thanks to its confirmed nature as the remnant of a standard Type Ia supernova from spectroscopy of its light echo, Tycho’s supernova remnant is a unique object that can provide a new perspective into thermonuclear supernova explosions. More than 400 years after its discovery as a supernova in November 1572, the remnant is now spread out over an 8 arcminute diameter region in a fairly symmetric, but patchy, shell-like morphology. The remnant’s thermal X-ray emission is dominated by a strong Si K$alpha$ line and also shows line emission from other species such as S, Ar, Ca, and Fe. Existing proper motion and X-ray line width measurements indicate that Tycho’s Si-rich ejecta shell is expanding at $sim$4700 km s$^{-1}$

We have taken advantage of the huge number of Si line photons in the 750-ks {it Chandra} ACIS observation from 2009 to make the first direct velocity measurements of ejecta in Tycho. The patchy nature of the ejecta shell allows for identification of red- and blue-shifted clumps of emission from the receding and approaching hemispheres. We use nonequilibrium ionization thermal models to jointly fit both ACIS-S and ACIS-I observations to determine the radial expansion velocity of individual clumps and associated systematic uncertainty. Red-shifted clumps have speeds of 3500–7800 km s$^{-1}$ and blue-shifted clumps 1600–5000 km s$^{-1}$ with a systematic uncertainty of 500-2000 km s$^{-1}$ determined by intercomparison of the ACIS-S and ACIS-I spectral results.

From our {it Chandra} radial analysis of surface brightness, centroid energy, and line width, we have confirmed previous line width measurements from {it Suzaku}, but are able to utilize finer radial bins that reveal additional structure in the kinematics of Tycho. In particular the Si and S line widths reach a deep minimum at the position of the peak surface brightness near the remnant’s edge and where Doppler broadening from the shell expansion is minimum. From the measured line widths and assuming that Doppler and turbulent broadening can be neglected, we estimate ion temperatures of 1.2$^{+0.2}_{-0.1}$ MeV and 1.2$^{+0.4}_{-0.6}$ MeV for Si and S, respectively. The electron temperature we measure in the Si-rich ejecta is $sim$1 keV, so the electron-to-ion temperature ratio is $beta = T_e/T_{rm ion} sim 0.001$, broadly consistent with spherically symmetric 1-D hydrodynamical models for Tycho.

The research was partially supported by NASA grant NNX15AK71G, funds from Rutgers University, Tokyo Metropolitan University, and the Institute of Space and Astronautical Science, as well as a JSPS Graduate Fellowship.