Serendipitous discovery of the unidentified extended TeV γ-ray source HESS J1303-631

¹ Max-Planck-Institut für Kernphysik, Heidelberg, Germany
² Yerevan Physics Institute, Armenia
³ University of Durham, Department of Physics, UK
⁴ Centre d'Étude Spatiale des Rayonnements, CNRS/UPS, Toulouse, France
⁵ Universität Hamburg, Institut für Experimentalphysik, Germany, e-mail: matthias.beilicke@desy.de
⁶ APC, Paris, France
⁷ Institut für Physik, Humboldt-Universität zu Berlin, Germany
⁸ LUTH, UMR 8102 du CNRS, Observatoire de Paris, Section de Meudon, France
⁹ Laboratoire de Physique Théorique et Astroparticules, IN2P3/CNRS, Université Montpellier II, 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, 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 Laboratoire de Physique Nucléaire et de Hautes Énergies, IN2P3/CNRS, Universités Paris VI & VII, France
¹⁸ Institut für Theoretische Physik, Lehrstuhl IV: Weltraum und Astrophysik, Ruhr-Universität Bochum, Germany
¹⁹ Institute of Particle and Nuclear Physics, Charles University, Prague, Czech Republic
²⁰ University of Namibia, Windhoek, Namibia

Received: 5 April 2005
Accepted: 9 May 2005

Abstract

The serendipitous discovery of an unidentified extended TeV γ-ray source close to the galactic plane named HESS J1303-631 at a significance of 21 standard deviations is reported. The observations were performed between February and June 2004 with the HESS stereoscopic system of Cherenkov telescopes in Namibia. HESS J1303-631 was discovered roughly north of the binary system PSR B1259-63/SS 2883, the target object of the initial observation campaign which was also detected at TeV energies in the same field of view. HESS J1303-631 is extended with a width of an assumed intrinsic Gaussian emission profile of and the integral flux above is compatible with constant emission over the entire observational period of % of the Crab Nebula flux. The measured energy spectrum can be described by a power-law with a photon index of . Up to now, no counterpart at other wavelengths is identified. Various possible TeV production scenarios are discussed.