  Direct photon emission in heavy-ion collisions is calculated within a
relativistic micro+macro hybrid model and compared to the microscopic transport
model UrQMD. In the hybrid approach, the high-density part of the collision is
calculated by an ideal 3+1-dimensional hydrodynamic calculation, while the
early (pre-equilibrium-) and late (rescattering-) phase are calculated with the
transport model. Different scenarios of the transition from the macroscopic
description to the transport model description and their effects are studied.
The calculations are compared to measurements by the WA98-collaboration and
predictions for the future CBM-experiment are made.

Nuclear Theory