A&A 442, 1-10 (2005)
DOI: 10.1051/0004-6361:20052983

Discovery of the binary pulsar PSR B1259-63 in very-high-energy gamma rays around periastron with HESS

F. Aharonian¹, A. G. Akhperjanian², K.-M. Aye³, A. R. Bazer-Bachi⁴, M. Beilicke⁵, W. Benbow¹, D. Berge¹, P. Berghaus⁶, K. Bernlöhr^{1, 7}, C. Boisson⁸, O. Bolz¹, I. Braun¹, F. Breitling⁷, A. M. Brown³, J. Bussons Gordo⁹, P. M. Chadwick³, L.-M. Chounet¹⁰, R. Cornils⁵, L. Costamante^{1, 11}, B. Degrange¹⁰, A. Djannati-Ataï⁶, L. O'C. Drury¹², G. Dubus¹⁰, D. Emmanoulopoulos¹³, P. Espigat⁶, F. Feinstein⁹, P. Fleury¹⁰, G. Fontaine¹⁰, Y. Fuchs¹⁴, S. Funk¹, Y. A. Gallant⁹, B. Giebels¹⁰, S. Gillessen¹, J. F. Glicenstein¹⁵, P. Goret¹⁵, C. Hadjichristidis³, M. Hauser¹³, G. Heinzelmann⁵, G. Henri¹⁴, G. Hermann¹, J. A. Hinton¹, W. Hofmann¹, M. Holleran¹⁶, D. Horns¹, O. C. de Jager¹⁶, S. Johnston¹⁷, B. Khélifi¹, J. G. Kirk¹, Nu. Komin⁷, A. Konopelko^{1, 7}, I. J. Latham³, R. Le Gallou³, A. Lemière⁶, M. Lemoine-Goumard¹⁰, N. Leroy¹⁰, O. Martineau-Huynh¹⁸, T. Lohse⁷, A. Marcowith⁴, C. Masterson^{1, 11}, T. J. L. McComb³, M. de Naurois¹⁸, S. J. Nolan³, A. Noutsos³, K. J. Orford³, J. L. Osborne³, M. Ouchrif^{18, 11}, M. Panter¹, G. Pelletier¹⁴, S. Pita⁶, G. Pühlhofer^{1, 13}, M. Punch⁶, B. C. Raubenheimer¹⁶, M. Raue⁵, J. Raux¹⁸, S. M. Rayner³, I. Redondo^{10, 11}, A. Reimer¹⁹, O. Reimer¹⁹, J. Ripken⁵, L. Rob²⁰, L. Rolland¹⁸, G. Rowell¹, V. Sahakian², L. Saugé¹⁴, S. Schlenker⁷, R. Schlickeiser¹⁹, C. Schuster¹⁹, U. Schwanke⁷, M. Siewert¹⁹, O. Skjæraasen²¹, H. Sol⁸, R. Steenkamp²², C. Stegmann⁷, J.-P. Tavernet¹⁸, R. Terrier⁶, C. G. Théoret⁶, M. Tluczykont^{10, 11}, G. Vasileiadis⁹, C. Venter¹⁶, P. Vincent¹⁸, H. J. Völk¹ and S. J. Wagner<sup>13

1</sup>  Max-Planck-Institut für Kernphysik, Heidelberg, Germany
²  Yerevan Physics Institute, Yerevan, Armenia
³  University of Durham, Department of Physics, Durham, UK
⁴  Centre d'Étude Spatiale des Rayonnements, CNRS/UPS, Toulouse, France
⁵  Universität Hamburg, Institut für Experimentalphysik, Hamburg, Germany
⁶  APC, Paris, France
⁷  Institut für Physik, Humboldt-Universität zu Berlin, Berlin, Germany
    e-mail: schlenk@physik.hu-berlin.de
⁸  LUTH, UMR 8102 du CNRS, Observatoire de Paris, Meudon, France
⁹  Groupe d'Astroparticules de Montpellier, IN2P3/CNRS, Université Montpellier II, Montpellier, France
¹⁰  Laboratoire Leprince-Ringuet, IN2P3/CNRS, École Polytechnique, Palaiseau, France
¹¹  European Associated Laboratory for Gamma-Ray Astronomy, jointly supported by CNRS and MPG
¹²  Dublin Institute for Advanced Studies, Dublin, Ireland
¹³  Landessternwarte, Königstuhl, Heidelberg, Germany
¹⁴  Laboratoire d'Astrophysique de Grenoble, INSU/CNRS, Université Joseph Fourier, Grenoble, France
¹⁵  DAPNIA/DSM/CEA, CE Saclay, Gif-sur-Yvette, France
¹⁶  Unit for Space Physics, North-West University, Potchefstroom, South Africa
¹⁷  School of Physics, University of Sydney, Australia
¹⁸  Laboratoire de Physique Nucléaire et de Hautes Énergies, IN2P3/CNRS, Universités Paris VI & VII, Paris, France
¹⁹  Institut für Theoretische Physik, Lehrstuhl IV: Weltraum und Astrophysik, Ruhr-Universität Bochum, Germany
²⁰  Institute of Particle and Nuclear Physics, Charles University, Prague, Czech Republic
²¹  Institute of Theoretical Astrophysics, University of Oslo, Norway
²²  University of Namibia, Windhoek, Namibia

(Received 3 March 2005 / Accepted 2 June 2005)

Abstract
We report the discovery of very-high-energy (VHE) -ray emission of the binary system PSR B1259-63 / SS 2883 of a radio pulsar orbiting a massive, luminous Be star in a highly eccentric orbit. The observations around the 2004 periastron passage of the pulsar were performed with the four 13 m Cherenkov telescopes of the HESS experiment, recently installed in Namibia and in full operation since December 2003. Between February and June 2004, a -ray signal from the binary system was detected with a total significance above . The flux was found to vary significantly on timescales of days which makes PSR B1259-63 the first variable galactic source of VHE -rays observed so far. Strong emission signals were observed in pre- and post-periastron phases with a flux minimum around periastron, followed by a gradual flux decrease in the months after. The measured time-averaged energy spectrum above a mean threshold energy of 380 GeV can be fitted by a simple power law with a photon index and flux normalisation . This detection of VHE -rays provides unambiguous evidence for particle acceleration to multi-TeV energies in the binary system. In combination with coeval observations of the X-ray synchrotron emission by the RXTE and INTEGRAL instruments, and assuming the VHE -ray emission to be produced by the inverse Compton mechanism, the magnetic field strength can be directly estimated to be of the order of 1 G.

Key words: gamma-rays: observations -- stars: pulsars: individual: PSR B1259-63

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