  The pattern of angular correlations of hadrons with a (semi-)hard trigger
hadron in heavy-ion collisions has attracted considerable interest. In
particular, unexpected large angle structures on the away side (opposite to the
trigger) have been found. Several explanations have been brought forward, among
them Mach shockwaves and Cherenkov radiation. Most of these scenarios are
characterized by radial symmetry around the parton axis, thus angular
correlations also determine the rapidity dependence of the correlation. If the
observed correlations are remnants of an away side parton after interaction
with the medium created in the collision, pQCD allows to calculate the
distribution $P(y)$ of the away side partons in rapidity.
  The measured correlation then arises as a folding of $P(y)$ and the rapidity
structure of the correlation taking into account the detector acceptance. This
places non-trivial and rather stringent constraints on the underlying scenario.
We investigate these dependences and demonstrate that Mach shockwaves survive
this folding procedure well whereas Cherenkov radiation scenarios face new
challenges.
