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-Bachi (1) , M. Beilicke , W. Benbow , D. Berge , K. Bernlöhr , C. Boisson (2) , O. Bolz , V. Borrel (1) , I. Braun , F. Breitling , A. M. Brown , R. Bühler , I. Büsching , S. Carrigan , P. M. Chadwick , L.-M. Chounet (3) , R. Cornils , L. Costamante , B. Degrange (3) , H. J. Dickinson , A. Djannati-Ataï (4) , L. O'C. Drury , G. Dubus (3) , K. Egberts , D. Emmanoulopoulos , P. Espigat (5) , F. Feinstein (6) , E. Ferrero , G. Fontaine (3) , Seb. Funk , S. Funk , Y.A. Gallant (6) , B. Giebels (3) , J. F. Glicenstein (7) , P. Goret (7) , C. Hadjichristidis , D. Hauser , M. Hauser , G. Heinzelmann , G. Henri (8) , G. Hermann , J. A. Hinton , W. Hofmann , M. Holleran , D. Horns , A. Jacholkowska (6) , O. C. de Jager , B. Khélifi (3) , Nu. Komin , A. Konopelko , I. J. Latham , R. Le Gallou , A. Lemière (5) , M. Lemoine-Goumard (3) , T. Lohse , J. M. Martin , O. Martineau-Huynh , A. Marcowith (1) , 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. Pelletier (8) , S. Pita (5) , G. Pühlhofer , M. Punch (5) , B. C. Raubenheimer , M. Raue , S. M. Rayner , A. Reimer , O. Reimer , J. Ripken , L. Rob , L. Rolland , G. Rowell , V. Sahakian , L. Saugé (8) , S. Schlenker , R. Schlickeiser , U. Schwanke , H. Sol (2) , D. Spangler , F. Spanier , R. Steenkamp , C. Stegmann , G. Superina (3) , J.-P. Tavernet , R. Terrier (5) , C.G. Théoret (5) , M. Tluczykont (3) , C. van Eldik , G. Vasileiadis (6) , C. Venter , P. Vincent , H. J. Völk , S. J. Wagner , M. Ward

1 CESR - Centre d'étude spatiale des rayonnements
2 LUTH (UMR_8102) - Laboratoire Univers et Théories
3 LLR - Laboratoire Leprince-Ringuet
4 APC - AHE - APC - Astrophysique des Hautes Energies
5 APC (UMR_7164) - AstroParticule et Cosmologie
6 LPTA - Laboratoire de Physique Théorique et Astroparticules
7 DAPNIA - Département d'Astrophysique, de physique des Particules, de physique Nucléaire et de l'Instrumentation Associée
8 LAOG - Laboratoire d'Astrophysique de Grenoble

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.

Mots clés: gamma rays: observations; acceleration of particles; block hole physics; stars: binaries: close

Domaines: Cosmologie et astrophysique extra-galactique [astro-ph.CO]; Cosmologie et astrophysique extra-galactique [astro-ph.CO]; Astrophysique [astro-ph]

F. Aharonian, A. G. Akhperjanian, A. R. Bazer-Bachi, M. Beilicke, W. Benbow, et al.. 3.9 day orbital modulation in the TeV gamma-ray flux and spectrum from the X-ray binary LS 5039. Astronomy and Astrophysics - A&A, 2006, 460, pp.743-749. ⟨10.1051/0004-6361:20065940⟩. ⟨in2p3-00124857⟩