%0 Journal Article %T 3.9 day orbital modulation in the TeV gamma-ray flux and spectrum from the X-ray binary LS 5039 %+ Centre d'étude spatiale des rayonnements (CESR) %+ Laboratoire Univers et Théories (LUTH (UMR_8102)) %+ Laboratoire Leprince-Ringuet (LLR) %+ APC - Astrophysique des Hautes Energies (APC - AHE) %+ AstroParticule et Cosmologie (APC (UMR_7164)) %+ Laboratoire de Physique Théorique et Astroparticules (LPTA) %+ Département d'Astrophysique, de physique des Particules, de physique Nucléaire et de l'Instrumentation Associée (DAPNIA) %+ Laboratoire d'Astrophysique de Grenoble (LAOG) %A Aharonian, F. %A G. Akhperjanian, A. %A R. Bazer-Bachi, A. %A Beilicke, M. %A Benbow, W. %A Berge, D. %A Bernlöhr, K. %A Boisson, C. %A Bolz, O. %A Borrel, V. %A Braun, I. %A Breitling, F. %A M. Brown, A. %A Bühler, R. %A Büsching, I. %A Carrigan, S. %A M. Chadwick, P. %A Chounet, L.-M. %A Cornils, R. %A Costamante, L. %A Degrange, B. %A J. Dickinson, H. %A Djannati-Ataï, A. %A O'C. Drury, L. %A Dubus, G. %A Egberts, K. %A Emmanoulopoulos, D. %A Espigat, P. %A Feinstein, F. %A Ferrero, E. %A Fontaine, G. %A Funk, Seb. %A Funk, S. %A Gallant, Y.A. %A Giebels, B. %A F. Glicenstein, J. %A Goret, P. %A Hadjichristidis, C. %A Hauser, D. %A Hauser, M. %A Heinzelmann, G. %A Henri, G. %A Hermann, G. %A A. Hinton, J. %A Hofmann, W. %A Holleran, M. %A Horns, D. %A Jacholkowska, A. %A C. de Jager, O. %A Khélifi, B. %A Komin, Nu. %A Konopelko, A. %A J. Latham, I. %A Le Gallou, R. %A Lemière, A. %A Lemoine-Goumard, M. %A Lohse, T. %A M. Martin, J. %A Martineau-Huynh, O. %A Marcowith, A. %A Masterson, C. %A J. L. Mccomb, T. %A de Naurois, M. %A Nedbal, D. %A J. Nolan, S. %A Noutsos, A. %A J. Orford, K. %A L. Osborne, J. %A Ouchrif, M. %A Panter, M. %A Pelletier, G. %A Pita, S. %A Pühlhofer, G. %A Punch, M. %A C. Raubenheimer, B. %A Raue, M. %A M. Rayner, S. %A Reimer, A. %A Reimer, O. %A Ripken, J. %A Rob, L. %A Rolland, L. %A Rowell, G. %A Sahakian, V. %A Saugé, L. %A Schlenker, S. %A Schlickeiser, R. %A Schwanke, U. %A Sol, H. %A Spangler, D. %A Spanier, F. %A Steenkamp, R. %A Stegmann, C. %A Superina, G. %A Tavernet, J.-P. %A Terrier, R. %A Théoret, C.G. %A Tluczykont, M. %A van Eldik, C. %A Vasileiadis, G. %A Venter, C. %A Vincent, P. %A J. Völk, H. %A J. Wagner, S. %A Ward, M. %Z 8 pages, 8 figures, accepted for publication in Astronomy & Astrophysics %< avec comité de lecture %Z APC-06-94 %@ 0004-6361 %J Astronomy & Astrophysics - A&A %I EDP Sciences %V 460 %P 743-749 %8 2006 %D 2006 %Z astro-ph/0607192 %R 10.1051/0004-6361:20065940 %K gamma rays: observations %K acceleration of particles %K block hole physics %K stars: binaries: close %Z Physics [physics]/Astrophysics [astro-ph]/Cosmology and Extra-Galactic Astrophysics [astro-ph.CO] %Z Sciences of the Universe [physics]/Astrophysics [astro-ph]/Cosmology and Extra-Galactic Astrophysics [astro-ph.CO] %Z Sciences of the Universe [physics]/Astrophysics [astro-ph]Journal articles %X New observations of LS 5039, a High Mass X-ray Binary comprising a massive star and compact object, were carried out with the High Energy Stereoscopic System of Cherenkov Telescopes (H.E.S.S.) in 2005 at very high energy (VHE) gamma-ray energies. These observations reveal that its flux and energy spectrum are modulated with the 3.9 day orbital period of the binary system. This is the first time in gamma-ray astronomy that orbital modulation has been observed, and periodicity clearly established using ground-based gamma-ray detectors. The VHE gamma-ray emission is largely confined to half of the orbit, peaking around the inferior conjunction epoch of the compact object. For this epoch, there is also a hardening of the energy spectrum in the energy range between 0.2 TeV and a few TeV. The flux vs. orbital phase profile provides the first clear indication of gamma-ray absorption via pair production within an astrophysical source, a process which is expected to occur if the gamma-ray production site is situated within ~1 AU of the compact object. Moreover the production region size must be not significantly greater than the binary separation (~0.15 AU). Notably, these constraints are also considerably smaller than the collimated outflows or jets (extending out to ~1000 AU) observed in LS 5039. The spectral hardening could arise from variations with phase in the maximum electron energies, and/or the dominant VHE gamma-ray production mechanism. %G English %Z HESS %L in2p3-00124857 %U https://in2p3.hal.science/in2p3-00124857 %~ IN2P3 %~ OBSPM %~ CEA %~ INSU %~ METEO %~ UNIV-PARIS7 %~ X %~ UNIV-TLSE3 %~ UGA %~ LPTA %~ LLR %~ APC %~ CNRS %~ UNIV-GRENOBLE1 %~ UNIV-MONTP2 %~ CNES %~ OSUG %~ LUTH %~ OMP %~ OMP-CESR %~ X-LLR %~ LAOG %~ X-DEP %~ X-DEP-PHYS %~ DSM-IRFU %~ IRFU-APC %~ PSL %~ UNIV-MONTPELLIER %~ CEA-DRF %~ UNIV-PARIS %~ UP-SCIENCES %~ OBSPM-PSL %~ UNIV-UT3 %~ UT3-INP %~ UT3-TOULOUSEINP %~ UM1-UM2 %~ TEST-SEBASTIEN3