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Astronomy and Astrophysics 460 (2006) 743-749
3.9 day orbital modulation in the TeV gamma-ray flux and spectrum from the X-ray binary LS 5039
F. Aharonian, A. G. Akhperjanian, A. R. Bazer-Bachi1, M. Beilicke, W. Benbow, D. Berge, K. Bernlöhr, C. Boisson2, O. Bolz, V. Borrel1, I. Braun, F. Breitling, A. M. Brown, R. Bühler, I. Büsching, S. Carrigan, P. M. Chadwick, L.-M. Chounet3, R. Cornils, L. Costamante, B. Degrange3, H. J. Dickinson, A. Djannati-Ataï4, L. O'C. Drury, G. Dubus3, K. Egberts, D. Emmanoulopoulos, P. Espigat4, F. Feinstein5, E. Ferrero, G. Fontaine3, Seb. Funk, S. Funk, Y. A. Gallant5, B. Giebels3, J. F. Glicenstein6, P. Goret6, C. Hadjichristidis, D. Hauser, M. Hauser, G. Heinzelmann, G. Henri7, G. Hermann, J. A. Hinton, W. Hofmann, M. Holleran, D. Horns, A. Jacholkowska5, O. C. De Jager, B. Khélifi3, Nu. Komin, A. Konopelko, I. J. Latham, R. Le Gallou, A. Lemière4, M. Lemoine-Goumard3, T. Lohse, J. M. Martin, O. Martineau-Huynh, A. Marcowith1, C. Masterson, T. J. L. Mccomb, M. De Naurois, D. Nedbal, S. J. Nolan, A. Noutsos, K. J. Orford, J. L. Osborne, M. Ouchrif, M. Panter, G. Pelletier7, S. Pita4, G. Pühlhofer, M. Punch4, B. C. Raubenheimer, M. Raue, S. M. Rayner, A. Reimer, O. Reimer, J. Ripken, L. Rob, L. Rolland, G. Rowell, V. Sahakian, L. Saugé7, S. Schlenker, R. Schlickeiser, U. Schwanke, H. Sol2, D. Spangler, F. Spanier, R. Steenkamp, C. Stegmann, G. Superina3, J.-P. Tavernet, R. Terrier4, C.G. Théoret4, M. Tluczykont3, C. Van Eldik, G. Vasileiadis5, C. Venter, P. Vincent, H. J. Völk, S. J. Wagner, M. Ward
HESS Collaboration(s)

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.
1 :  CESR - Centre d'étude spatiale des rayonnements
2 :  LUTH - Laboratoire Univers et Théories
3 :  LLR - Laboratoire Leprince-Ringuet
4 :  APC - UMR 7164 - AstroParticule et Cosmologie
5 :  LPTA - Laboratoire de Physique Théorique et Astroparticules
6 :  DAPNIA - Département d'Astrophysique, de physique des Particules, de physique Nucléaire et de l'Instrumentation Associée
7 :  LAOG - Laboratoire d'Astrophysique de Grenoble
Physique/Astrophysique/Cosmologie et astrophysique extra-galactique

Planète et Univers/Astrophysique/Cosmologie et astrophysique extra-galactique

Planète et Univers/Astrophysique
gamma rays: observations – acceleration of particles – block hole physics – stars: binaries: close
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