  Stellar X-ray and UV radiation can significantly affect the survival,
composition, and long-term evolution of the atmospheres of planets in or near
their host star's habitable zone (HZ). Especially interesting are planetary
systems in the solar neighborhood that may host temperate and potentially
habitable surface conditions, which may be analyzed by future ground and
space-based direct-imaging surveys for signatures of habitability and life. To
advance our understanding of the radiation environment in these systems, we
leverage $\sim$3 Msec of XMM-Newton and Chandra observations in order to
measure three fundamental stellar properties at X-ray energies for 57 nearby
FGKM stellar systems: the shape of the stellar X-ray spectrum, the luminosity,
and the timescales over which the stars vary (e.g., due to flares). These
systems possess HZs that will be directly imageable to next-generation
telescopes such as the Habitable Worlds Observatory and ground-based Extremely
Large Telescopes (ELTs). We identify 29 stellar systems with $L_X/L_{\rm bol}$
ratios similar to (or less than) that of the Sun; any potential planets in the
habitable zones of these stars therefore reside in present day X-ray radiation
environments similar to (or less hostile than) modern Earth, though a broader
set of these targets could host habitable planets. An additional 19 stellar
systems have been observed with the Swift X-ray Telescope; in total, only
$\sim$30% of potential direct imaging target stars has been observed with
XMM-Newton, Chandra, or Swift. The data products from this work (X-ray light
curves and spectra) are available via a public Zenodo repository (doi:
10.5281/zenodo.11490574).
