  New multi-roll coronagraphic images of the HD 181327 debris disk obtained
using the Space Telescope Imaging Spectrograph (STIS) on board the Hubble Space
Telescope (HST) reveal the debris ring in its entirety at high S/N and
unprecedented spatial resolution. We present and apply a new multi-roll image
processing routine to identify and further remove quasi-static PSF-subtraction
residuals and quantify systematic uncertainties. We also use a new iterative
image deprojection technique to constrain the true disk geometry and
aggressively remove any surface brightness asymmetries that can be explained
without invoking dust density enhancements/deficits. The measured empirical
scattering phase function for the disk is more forward scattering than
previously thought and is not well-fit by a Henyey-Greenstein function. The
empirical scattering phase function varies with stellocentric distance,
consistent with the expected radiation pressured-induced size segregation
exterior to the belt. Within the belt, the empirical scattering phase function
contradicts unperturbed debris ring models, suggesting the presence of an
unseen planet. The radial profile of the flux density is degenerate with a
radially-varying scattering phase function; therefore estimates of the ring's
true width and edge slope may be highly uncertain. We detect large scale
asymmetries in the disk, consistent with either the recent catastrophic
disruption of a body with mass >1% the mass of Pluto, or disk warping due to
strong interactions with the interstellar medium (ISM).
