  We present two different search methods for electromagnetic counterparts to
gravitational-wave (GW) events from ground-based detectors using archival NASA
high-energy data from the Fermi-GBM and RXTE-ASM instruments. To demonstrate
the methods, we use a limited number of representative GW background noise
events produced by a search for binary neutron star coalescence over the last
two months of the LIGO-Virgo S6/VSR3 joint science run. Time and sky location
provided by the GW data trigger a targeted search in the high-energy photon
data. We use two custom pipelines: one to search for prompt gamma-ray
counterparts in GBM, and the other to search for a variety of X-ray afterglow
model signals in ASM. We measure the efficiency of the joint pipelines to weak
gamma-ray burst counterparts, and a family of model X-ray afterglows. By
requiring a detectable signal in either electromagnetic instrument coincident
with a GW event, we are able to reject a large majority of GW candidates. This
reduces the signal-to-noise of the loudest surviving GW background event by
around 15-20%.
