  We calculate the properties, occurrence rates and detection prospects of
individually resolvable 'single sources' in the low frequency gravitational
wave (GW) spectrum. Our simulations use the population of galaxies and massive
black hole binaries from the Illustris cosmological hydrodynamic simulations,
coupled to comprehensive semi-analytic models of the binary merger process.
Using mock pulsar timing arrays (PTA) with, for the first time, varying
red-noise models, we calculate plausible detection prospects for GW single
sources and the stochastic GW background (GWB). Contrary to previous results,
we find that single sources are at least as detectable as the GW background.
Using mock PTA, we find that these 'foreground' sources (also
'deterministic'/'continuous') are likely to be detected with $\sim 20 \,
\textrm{yr}$ total observing baselines. Detection prospects, and indeed the
overall properties of single sources, are only moderately sensitive to binary
evolution parameters---namely eccentricity & environmental coupling, which can
lead to differences of $\sim 5 \,\textrm{yr}$ in times to detection. Red noise
has a stronger effect, roughly doubling the time to detection of the foreground
between a white-noise only model ($\sim 10$ - $15 \, \textrm{yr}$) and severe
red noise ($\sim 20$ - $30 \, \textrm{yr}$). The effect of red noise on the GWB
is even stronger, suggesting that single source detections may be more robust.
We find that typical signal-to-noise ratios for the foreground peak near $f =
0.1 \, \textrm{yr}^{-1}$, and are much less sensitive to the continued addition
of new pulsars to PTA.
