Irradiation of an Accretion Disc by a Jet: General Properties and
  Implications for Spin Measurements of Black Holes
  X-ray irradiation of the accretion disc leads to strong reflection features,
which are then broadened and distorted by relativistic effects. We present a
detailed, general relativistic approach to model this irradiation for different
geometries of the primary X-ray source. These geometries include the standard
point source on the rotational axis as well as more jet-like sources, which are
radially elongated and accelerating. Incorporating this code in the relline
model for relativistic line emission, the line shape for any configuration can
be predicted. We study how different irradiation geometries affect the
determination of the spin of the black hole. Broad emission lines are produced
only for compact irradiating sources situated close to the black hole. This is
the only case where the black hole spin can be unambiguously determined. In all
other cases the line shape is narrower, which could either be explained by a
low spin or an elongated source. We conclude that for all those cases and
independent of the quality of the data, no unique solution for the spin exists
and therefore only a lower limit of the spin value can be given.
