H.E.S.S. observations of LS 5039 |
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Authors: | Mathieu de Naurois |
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Institution: | (1) Laboratoire de Physique Nucléaire et de Hautes Energies, 4 place Jussieu, 75252 Paris Cedex 05, France |
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Abstract: | 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) γ-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 γ-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 (∼1 AU), thus excluding the large scale collimated outflows
or jets (extending out to ∼1000 AU). 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 γ-ray production mechanism. This first-time observation of modulated γ-ray emission allows precise tests of the acceleration and emission models in binary systems.
Mathieu de Naurois for the H.E.S.S. Collaboration. |
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Keywords: | Gamma rays: observations X-rays: binaries Individual objects: LS 5039 (HESS J1826-148) |
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