We present dilepton spectra from p+p and p+Nb collisions at a kinetic beam energy of 3.5 GeV, which were simulated with the GiBUU transport model assuming different in-medium scenarios. We compare these spectra to preliminary HADES data and show that
GiBUU can describe the data reasonably well. Our simulations indicate that the intermediate dilepton-mass region is sensitive to the N-Delta electromagnetic transition form factor, which up to now is unmeasured in the time-like region.
