Kaon production at subthreshold energies - what do we learn about the nuclear medium ?

The Isospin Quantum Molecular Dynamics model is used to compare spectra and elliptic flow of kaons produced at subthreshold energies with data taken at the SIS accelerator at GSI. We find that temperatures of the spectra are dominated by the rescattering of the kaons. The study of elliptic flow observables indicates the influence of rescattering as well as of the optical potential of the kaons with increasing dominance of the optical potential at lower incident energies.