  HD 15137 is an intriguing runaway O-type binary system that offers a rare
opportunity to explore the mechanism by which it was ejected from the open
cluster of its birth. Here we present recent blue optical spectra of HD 15137
and derive a new orbital solution for the spectroscopic binary and physical
parameters of the O star primary. We also present the first XMM-Newton
observations of the system. Fits of the EPIC spectra indicate soft, thermal
X-ray emission consistent with an isolated O star. Upper limits on the
undetected hard X-ray emission place limits on the emission from a proposed
compact companion in the system, and we rule out a quiescent neutron star in
the propellor regime or a weakly accreting neutron star. An unevolved secondary
companion is also not detected in our optical spectra of the binary, and it is
difficult to conclude that a gravitational interaction could have ejected this
runaway binary with a low mass optical star. HD 15137 may contain an elusive
neutron star in the ejector regime or a quiescent black hole with conditions
unfavorable for accretion at the time of our observations.
