  X-ray observations of low-mass stars in open clusters are critical to
understanding the dependence of magnetic activity on stellar properties and
their evolution. Praesepe and the Hyades, two of the nearest, most-studied open
clusters, are among the best available laboratories for examining the
dependence of magnetic activity on rotation for stars with masses lower than
$\approx 1\ M_{\odot}$. We present an updated study of the rotation X-ray
activity relation in the two clusters. We updated membership catalogs that
combine pre-Gaia catalogs with new catalogs based on Gaia Data Release 2. The
resulting catalogs are the most inclusive ones for both clusters: 1739 Praesepe
and 1315 Hyades stars. We collected X-ray detections for cluster members, for
which we analyzed, re-analyzed, or collated data from ROSAT, the Chandra X-ray
Observatory, the Neil Gehrels Swift Observatory, and XMM-Newton. We have
detections for 326 Praesepe and 462 Hyades members, of which 273 and 164,
respectively, have rotation periods, an increase of 6$\times$ relative to what
was previously available. We find that at $\approx$700 Myr, only M dwarfs
remain saturated in X-rays, with only tentative evidence for supersaturation.
We also find a tight relation between the Rossby number and fractional X-ray
luminosity $L_\mathrm{X}/L_\mathrm{bol}$ in unsaturated single members,
suggesting a power-law index between $-3.2$ and $-3.9$. Lastly, we find no
difference in the coronal parameters between binary and single members. These
results provide essential insight into the relative efficiency of magnetic
heating of the stars' atmospheres, thereby informing the development of robust
age-rotation-activity relations.
