  Recent observations have accumulated compelling evidence that some short
gamma-ray bursts (SGRBs) are associated with the mergers of neutron star (NS)
binaries. This would indicate that the SGRB event is associated with a
gravitational-wave (GW) signal corresponding to the final inspiral of the
compact binary. In addition, the radioactive decay of elements produced in NS
binary mergers may result in transients visible in the optical and infrared
with peak luminosities on hours-days timescales. Simultaneous observations of
the inspiral GWs and signatures in the electromagnetic band may allow us to
directly and independently determine both the luminosity distance and redshift
to a binary. These standard sirens (the GW analog of standard candles) have the
potential to provide an accurate measurement of the low-redshift Hubble flow.
In addition, these systems are absolutely calibrated by general relativity, and
therefore do not experience the same set of astrophysical systematics found in
traditional standard candles, nor do the measurements rely on a distance
ladder. We show that 15 observable GW and EM events should allow the Hubble
constant to be measured with 5% precision using a network of detectors that
includes advanced LIGO and Virgo. Measuring 30 beamed GW-SGRB events could
constrain H_0 to better than 1%. When comparing to standard Gaussian likelihood
analysis, we find that each event's non-Gaussian posterior in H_0 helps reduce
the overall measurement errors in H_0 for an ensemble of NS binary mergers.
