  The coalescence of black hole-neutron star binaries is expected to be a
principal source of gravitational waves for the next generation of detectors,
Advanced LIGO and Advanced Virgo. Ideally, these and other gravitational wave
sources would have a distinct electromagnetic counterpart, as significantly
more information could be gained through two separate channels. In addition,
since these detectors will probe distances with non-negligible redshift, a
coincident observation of an electromagnetic counterpart to a gravitational
wave signal would facilitate a novel measurement of dark energy [1]. For black
hole masses not much larger than the neutron star mass, the tidal disruption
and subsequent accretion of the neutron star by the black hole provides one
avenue for generating an electromagnetic counterpart [2]. However, in this
work, we demonstrate that, for all black hole-neutron star binaries observable
by Advanced LIGO/Virgo, the interaction of the black hole with the magnetic
field of the neutron star will drive a Poynting flux. This Poynting flux
generates synchrotron/curvature radiation as the electron-positron plasma in
the neutron star magnetosphere is accel- erated, and thermal radiation as the
plasma is focused onto the neutron star magnetic poles, creating a "hot spot"
on the neutron star surface. This novel effect will gener- ate copious
luminosity, comparable to supernovae and active galactic nuclei, so that black
hole-neutron star coalescences detectable with gravitational waves by Advanced
LIGO/Virgo could also potentially be detectable electromagnetically.
