  Black hole-neutron star (BHNS) binaries are amongst promising candidates for
the joint detection of electromagnetic (EM) signals with gravitational waves
(GWs) and are expected to be detected in the near future. Here we study the
effect of the BHNS binary parameters on the merger ejecta properties and
associated EM signals. We estimate the remnant disk and unbound ejecta masses
for BH mass and spin distributions motivated from the observations of transient
low-mass X-ray binaries (LMXBs) and specific NS equation of state (EoS). The
amount of r-process elements synthesised in BHNS mergers is estimated to be a
factor of $\sim 10^{2}-10^{4}$ smaller than BNS mergers, due to the smaller
dynamical ejecta and merger rates for the former. We compute the EM
luminosities and light curves for the early- and late-time emissions from the
ultra-relativistic jet, sub-relativistic dynamical ejecta and wind, and the
mildly-relativistic cocoon for typical ejecta parameters. We then evaluate the
low-latency EM follow-up rates of the GW triggers in terms of the GW detection
rate $\dot{N}_{GW}$ for current telescope sensitivities and typical BHNS binary
parameters to find that most of the EM counterparts are detectable for high BH
spin, small BH mass and stiffer NS EoS when NS disruption is significant. Based
on the relative detection rates for given binary parameters, we find the ease
of EM follow-up to be: ejecta afterglow $>$ cocoon afterglow $\gtrsim$ jet
prompt $>$ ejecta macronova $>$ cocoon prompt $>$ jet afterglow $>>$ wind
macronova $>>$ wind afterglow.

High Energy Astrophysical Phenomena