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

¹ 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) γ-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 γ-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 γ-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 γ-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 γ-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.