The Exceptional X-ray Evolution of SN1996cr in High Resolution
  We present X-ray spectra spanning 18 years of evolution for SN\,1996cr, one
of the five nearest SNe detected in the modern era. {\it Chandra} HETG
exposures in 2000, 2004, and 2009 allow us to resolve spectrally the velocity
profiles of Ne, Mg, Si, S, and Fe emission lines and monitor their evolution as
tracers of the ejecta-circumstellar medium (CSM) interaction. To explain the
diversity of X-ray line profiles, we explore several possible geometrical
models. Based on the highest signal-to-noise 2009 epoch, we find that a polar
geometry with two distinct opening angle configurations and internal
obscuration can successfully reproduce all of the observed line profiles. The
best fit model consists of two plasma components: (1) a mildly absorbed
(2$\times$10$^{21}$\,cm$^{-2}$), cooler ($\approx$2\,keV) with high Ne, Mg, Si,
and S abundances associated with a wide polar interaction region (half-opening
angle $\approx$58$^{\circ}$); (2) a moderately absorbed
(2$\times$10$^{22}$\,cm$^{-2}$), hotter (>~20\,keV) plasma with high Fe
abundances and strong internal obscuration associated with a narrow polar
interaction region (half-opening angle $\approx$20$^{\circ}$). We extend this
model to seven further epochs with lower signal-to-noise ratio and/or lower
spectral-resolution between 2000-2018, yielding several interesting trends in
absorption, flux, geometry and expansion velocity. We argue that the hotter and
colder components are associated with reflected and forward shocks,
respectively, at least at later epochs. We discuss the physical implications of
our results and plausible explosion scenarios to understand the X-ray data of
SN\,1996cr.
