Observations of the TeV γ‐Ray Binaries PSR B1259—63/SS2883 and LS 5039 with H.E.S.S.

PSR B1259—63/SS 2883, which became known as the first galactic variable TeV γ‐ray emitter since its discovery in the very high energy (VHE) regime by H.E.S.S. in 2004, as well as LS 5039 are two out of four up to now known TeV γ‐ray binaries. While PSR B1259—63 is the only known binary plerion seen in this energy band, where the generation of TeV photons can be unambiguously traced back to pulsar wind (PW) interactions, LS 5039 is likely to be a microquasar and therefore accretion driven. However, the exact origins for VHE radiation in LS 5039 are still under debate. As binary plerion PSR B1259—63 is a unique laboratory for the study of PW shock dynamics with respect to interactions with ambient radiation and matter fields around a companion star. The PW interactions in PSR B1259—63 are thought to become most efficient around the system’s periastron passage, occurring only every ∼3.4 years on the eccentric pulsar orbit around SS2883. A 60h H.E.S.S. observation campaign on PSR B1259—63 from April to August 2007 also covered orbital phases prior to periastron (July 27th) which were up to now unexplored in VHE γ‐rays. The outline and motivation of this campaign will be discussed. Moreover, LS 5039 data will be reviewed. The flux modulation found in this VHE source provides the first indications for attenuation effects of γ‐rays in the intense stellar photon field in this system. The observed spectral features, however, contradict a pure absorption by pair production scenario for LS 5039.