Parameter Estimation of Gravitational Waves from Nonprecessing BH-NS
  Inspirals with higher harmonics: Comparing MCMC posteriors to an Effective
  Fisher Matrix
  Using the \texttt{lalinference} Markov-chain Monte Carlo parameter estimation
code, we examine two distinct nonprecessing black hole-neutron star (BH-NS)
binaries with and without higher-order harmonics. Our simulations suggest that
higher harmonics provide a minimal amount of additional information,
principally about source geometry. Higher harmonics do provide
disproportionately more information than expected from the signal power. Our
results compare favorably to the "effective Fisher matrix" approach.
Extrapolating using analytic scalings, we expect higher harmonics will provide
little new information about nonprecessing BH-NS binaries at the signal
amplitudes expected for the first few detections. Any study of subdominant
degrees of freedom in gravitational wave astronomy can adopt the tools
presented here ($V/V_{\rm prior}$ and $D_{KL}$) to assess whether new physics
is accessible (e.g., modifications of gravity; spin-orbit misalignment) and if
so precisely what information those new parameters provide. For
astrophysicists, we provide a concrete illustration of how well parameters of a
BH-NS binary can be measured, relevant to the astrophysical interpretation of
coincident EM and GW events (e.g., short GRBs). For our fiducial
initial-detector example, the individual masses can be determined to lie
between $7.11-11.48 M_\odot$ and $1.77-1.276M_\odot$ at greater than 99%
confidence, accounting for unknown BH spin. Assuming comparable control over
waveform systematics, future measurements of BH-NS binaries can constrain the
BH and perhaps NS mass distributions.
