  We report on the discovery of a new extremely short period transiting
extrasolar planet, WASP-19b. The planet has mass Mpl = 1.15 \pm 0.08 MJ, radius
Rpl = 1.31 \pm 0.06 RJ, and orbital period P = 0.7888399 \pm 0.0000008 days.
Through spectroscopic analysis, we determine the host star to be a slightly
super-solar metallicity ([M/H] = 0.1 \pm 0.1 dex) G-dwarf with Teff = 5500 \pm
100 K. In addition, we detect periodic, sinusoidal flux variations in the light
curve which are used to derive a rotation period for the star of Prot = 10.5
\pm 0.2 days. The relatively short stellar rotation period suggests that either
WASP-19 is somewhat young (~ 600 Myr old) or tidal interactions between the two
bodies have caused the planet to spiral inward over its lifetime resulting in
the spin-up of the star. Due to the detection of the rotation period, this
system has the potential to place strong constraints on the stellar tidal
quality factor, Q's, if a more precise age is determined.
