  The origin of rapid neutron capture (r-process) nuclei remains one of the
longest standing mysteries in nuclear astrophysics. Core collapse supernovae
(SNe) and neutron star binary mergers are likely r-process sites, but little
evidence yet exists for their in situ formation in such environments. Motivated
by the advent of sensitive new or planned X-ray telescopes such as the Nuclear
Spectroscopic Telescope Array (NuSTAR) and the Large Observatory for X-ray
Timing (LOFT), we revisit the prospects for the detection of X-ray decay lines
from r-process nuclei in young or nearby supernova remnants. For all remnants
planned to be observed by NuSTAR (and several others), we conclude that
r-process nuclei are detectable only if the remnant possesses a large
overabundance O > 1e3 relative to the average yield per SN. Prospects are
better for the next Galactic SN (assumed age of 3 years and distance of 10
kpc), for which an average r-process yield is detectable via the 10.7(9.2) keV
line complexes of Os194 by LOFT at 6 sigma (5 sigma) confidence; the 27.3 keV
line complex of Sb125 is detectable by NuSTAR at 2 sigma for O > 2. We also
consider X-rays lines from the remnants of Galactic magnetars, motivated by the
much higher r-process yields of the magneto-rotationally driven SNe predicted
to birth magnetars. The ~ 3.6-3.9 keV lines of Sn126 are potentially detectable
in the remnants of the magnetars 1E1547.0-5408 and 1E2259+586 by LOFT for an
assumed r-process yield predicted by recent simulations. The (non-)detection of
these lines can thus probe whether magnetars are indeed born with millisecond
periods. Finally, we consider a blind survey of the Galactic plane with LOFT
for r-process lines from the most recent binary neutron star merger remnant,
concluding that a detection is unlikely without additional information on the
merger location.
