  While various methods have been proposed to disentangle the progenitor system
for Type Ia supernovae, their origin is still unclear. Circumstellar
environment is a key to distinguishing between the double-degenerate (DD) and
single-degenerate (SD) scenarios since a dense wind cavity is expected only in
the case of the SD system. We perform spatially resolved X-ray spectroscopy of
Tycho's supernova remnant (SNR) with XMM-Newton and reveal the
three-dimensional velocity structure of the expanding shock-heated ejecta
measured from Doppler-broadened lines of intermediate-mass elements. Obtained
velocity profiles are fairly consistent with those expected from a uniformly
expanding ejecta model near the center, whereas we discover a rapid
deceleration ($\sim4000$ km s$^{-1}$ to $\sim1000$ km s$^{-1}$) near the edge
of the remnant in almost every direction. The result strongly supports the
presence of a dense wall entirely surrounding the remnant, which is confirmed
also by our hydrodynamical simulation. We thus conclude that Tycho's SNR is
likely of the SD origin. Our new method will be useful for understanding
progenitor systems of Type Ia SNRs in the era of high-angular/energy resolution
X-ray astronomy with microcalorimeters.
