  We present results from a study of 2-8 keV X-ray sources detected by the
Advanced CCD Imaging Spectrometer (ACIS) instrument on the Chandra X-ray
Observatory in the field of the z=0.516 cluster CRSS J0030.5+2618. In our 63.5
arcmin^2 search area, we detect 10 sources with 2-8 keV fluxes down to
approximately 4x10^{-15} erg cm^{-2} s$^{-1}; our lowest flux sources are
approximately 10 times fainter than those previously available for study in
this band. Our derived source density is about an order of magnitude larger
than previous source counts above 2 keV, although this density may be enhanced
somewhat due to the presence of the cluster. We detail our methods for source
detection and characterization, and we show that the resulting source list and
parameters are robust. We have used the Marcario Low Resolution Spectrograph on
the Hobby-Eberly Telescope to obtain optical spectra for several of our
sources; combining these spectra with archival data we find that the sources
appear to be active galaxies, often with narrow permitted lines, red optical
continua or hard X-ray spectra. Four of the X-ray sources are undetected to
R=21.7; if they reside in L* galaxies they must have z > 0.55-0.75 and hard
X-ray luminosities of L_{2-8} > 4x10^{42} erg s^{-1}. We detect all but one of
our 2-8 keV sources in the 0.2-2 keV band as well. This result extends to
significantly lower fluxes the constraints on any large, completely new
population of X-ray sources that appears above 2-3 keV.
