  We report precise radial velocity (RV) measurements of WASP-47, a G star that
hosts three transiting planets in close proximity (a hot Jupiter, a super-Earth
and a Neptune-sized planet) and a non-transiting planet at 1.4 AU. Through a
joint analysis of previously published RVs and our own Keck-HIRES RVs, we
significantly improve the planet mass and bulk density measurements. For the
super-Earth WASP-47e ($P$ = 0.79 days), we measure a mass of 9.11 $\pm$ 1.17
$M_\oplus$, and a bulk density of 7.63 $\pm$ 1.90 g cm$^{-3}$, consistent with
a rocky composition. For the hot Jupiter WASP-47b ($P$ = 4.2 days), we measure
a mass of 356 $\pm$ 12 $M_\oplus$ (1.12 $\pm$ 0.04 $M_\rm{Jup}$) and constrain
its eccentricity to $<0.021$ at 3-$\sigma$ confidence. For the Neptune-size
planet WASP-47d ($P$ = 9.0 days), we measure a mass of 12.75 $\pm$ 2.70
$M_\oplus$, and a bulk density of 1.36 $\pm$ 0.42 g cm$^{-3}$, suggesting it
has a thick H/He envelope. For the outer non-transiting planet, we measure a
minimum mass of 411 $\pm$ 18 $M_\oplus$ (1.29 $\pm$ 0.06 $M_\rm{Jup}$), an
orbital period of 595.7 $\pm$ 5.0 days, and an orbital eccentricity of 0.27
$\pm$ 0.04. Our new measurements are consistent with but 2$-$4$\times$ more
precise than previous mass measurements.
