  We present far-infrared and sub-millimeter images of the eta Crv debris disk
system obtained with Herschel and SCUBA-2, as well as Hubble Space Telescope
visible and near-infrared coronagraphic images. In the 70 micron Herschel
image, we clearly separate the thermal emission from the warm and cold belts in
the system, find no evidence for a putative dust population located between
them, and precisely determine the geometry of the outer belt. We also find
marginal evidence for azimuthal asymmetries and a global offset of the outer
debris ring relative to the central star. Finally, we place stringent upper
limits on the scattered light surface brightness of the outer ring. Using
radiative transfer modeling, we find that it is impossible to account for all
observed properties of the system under the assumption that both rings contain
dust populations with the same properties. While the outer belt is in
reasonable agreement with the expectations of steady-state collisional cascade
models, albeit with a minimum grain size that is four times larger than the
blow-out size, the inner belt appears to contain copious amounts of small dust
grains, possibly below the blow-out size. This suggests that the inner belt
cannot result from a simple transport of grains from the outer belt and rather
supports a more violent phenomenon as its origin. We also find that the
emission from the inner belt has not declined over three decades, a much longer
timescale than its dynamical timescale, which indicates that the belt is
efficiently replenished.
