The Nature of LS 5039

The number of gamma-ray binary candidates has been increasing in recent years, yet we are still far from understanding the physical processes that take place in these extreme systems. In most cases we even cannot differentiate between a NS and a BH. We propose contemporaneous XMM-Newton and NuSTAR observations around the superior conjunction phase of the gamma-ray microquasar LS 5039. With the outstanding timing resolution of EPIC-PN in Timing mode and the acquired contemporaneous soft-to-hard X-ray spectrum, we can search for pulsar or BH signatures using timing and spectral information.