A search for very high energy γ-ray emission from the starburst galaxy NGC 253 with HESS 

¹ Max-Planck-Institut für Kernphysik, Heidelberg, Germany e-mail: Jim.Hinton@mpi-hd.mpg.de
² Yerevan Physics Institute, Armenia
³ Centre d'Étude Spatiale des Rayonnements, CNRS/UPS, Toulouse, France
⁴ Universität Hamburg, Institut für Experimentalphysik, Germany
⁵ Institut für Physik, Humboldt-Universität zu Berlin, Germany
⁶ LUTH, UMR 8102 du CNRS, Observatoire de Paris, Section de Meudon, France
⁷ University of Durham, Department of Physics, UK
⁸ Laboratoire Leprince-Ringuet, IN2P3/CNRS, École Polytechnique, Palaiseau, France
⁹ European Associated Laboratory for Gamma-Ray Astronomy, jointly supported by CNRS and MPG
¹⁰ APC, Paris, France (UMR 7164, CNRS, Université Paris VII, CEA, Observatoire de Paris)
¹¹ Dublin Institute for Advanced Studies, Ireland
¹² Landessternwarte, Königstuhl, Heidelberg, Germany
¹³ Laboratoire de Physique Théorique et Astroparticules, IN2P3/CNRS, Université Montpellier II, France
¹⁴ Laboratoire d'Astrophysique de Grenoble, INSU/CNRS, Université Joseph Fourier, France
¹⁵ DAPNIA/DSM/CEA, CE Saclay, Gif-sur-Yvette, Cedex, 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, Paris, 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: 26 May 2005
Accepted: 12 July 2005

Abstract

We present the result of 28 h of observations of the nearby starburst galaxy NGC 253 with the HESS detector in 2003. We find no evidence for very high energy γ-ray emission from this object. Gamma-ray emission above 400 GeV from NGC 253 had been reported by the CANGAROO collaboration in 2002. From the HESS data we derive upper limits on the flux above 300 GeV of photons cm^-2 s^-1 for a point-like source and photons cm^-2 s^-1 for a source of radius 0.5° as reported by CANGAROO, both at a confidence level of 99%. These upper limits are inconsistent with the spectrum reported by CANGAROO. The expected very high energy γ-ray emission from this object is discussed in the framework of a galactic wind propagation model.