出版社：SISSA, Scuola Internazionale Superiore di Studi Avanzati
摘要：Recent observations of the binary system LS 5039 with the High Energy Stereoscopic System
(H.E.S.S.) revealed that its Very High Energy (VHE) g-ray emission is modulated at the 3.9 days
orbital period of the system. The bulk of the emission is largely confined to half of the orbit, peaking
around the inferior conjunction epoch of the compact object. The flux modulation provides
the first indication of g-ray absorption by pair production on the intense stellar photon field. This
implies that the production region size must be not significantly greater than the gamma-gamma
photosphere size (» 1AU), thus excluding the large scale collimated outflows or jets (extending
out to » 1000AU). A hardening of the spectrum is also observed at the same epoch between 0.2
and a few TeV which is unexpected under a pure absorption scenario and could rather arise from
variation with phase in the maximum electron energy and/or the dominant VHE g-ray production
mechanism. This first-time observation of modulated g-ray emission allows precise tests of the
acceleration and emission models in binary systems.
