Letter to the Editor

First detection of a VHE gamma-ray spectral maximum from a cosmic source: HESS discovery of the Vela X nebula

¹ Max-Planck-Institut für Kernphysik, PO Box 103980, 69029 Heidelberg, Germany
² Yerevan Physics Institute, 2 Alikhanian Brothers St., 375036 Yerevan, Armenia
³ Centre d'Étude Spatiale des Rayonnements, CNRS/UPS, 9 Av. du Colonel Roche, BP 4346, 31029 Toulouse Cedex 4, France
⁴ Universität Hamburg, Institut für Experimentalphysik, Luruper Chaussee 149, 22761 Hamburg, Germany
⁵ Institut für Physik, Humboldt-Universität zu Berlin, Newtonstr. 15, 12489 Berlin, Germany
⁶ LUTH, UMR 8102 du CNRS, Observatoire de Paris, Section de Meudon, 92195 Meudon Cedex, France
⁷ University of Durham, Department of Physics, South Road, Durham DH1 3LE, UK
⁸ Unit for Space Physics, North-West University, Potchefstroom 2520, South Africa
⁹ Laboratoire Leprince-Ringuet, IN2P3/CNRS, École Polytechnique, 91128 Palaiseau, France
¹⁰ European Associated Laboratory for Gamma-Ray Astronomy, jointly supported by CNRS and MPG
¹¹ APC, 11 Place Marcelin Berthelot, 75231 Paris Cedex 05, UMR 7164, CNRS, Université Paris VII, CEA, Observatoire de Paris, France
¹² Dublin Institute for Advanced Studies, 5 Merrion Square, Dublin 2, Ireland
¹³ Landessternwarte, Universität Heidelberg, Königstuhl, 69117 Heidelberg, Germany
¹⁴ Laboratoire de Physique Théorique et Astroparticules, IN2P3/CNRS, Université Montpellier II, CC 70, Place Eugène Bataillon, 34095 Montpellier Cedex 5, France
¹⁵ DAPNIA/DSM/CEA, CE Saclay, 91191 Gif-sur-Yvette, Cedex, France
¹⁶ Laboratoire d'Astrophysique de Grenoble, INSU/CNRS, Université Joseph Fourier, BP 53, 38041 Grenoble Cedex 9, France
¹⁷ Institut für Astronomie und Astrophysik, Universität Tübingen, Sand 1, 72076 Tübingen, Germany
¹⁸ Laboratoire de Physique Nucléaire et de Hautes Energies, IN2P3/CNRS, Universités Paris VI & VII, 4 Place Jussieu, 75252 Paris Cedex 5, France
¹⁹ Institute of Particle and Nuclear Physics, Charles University, V Holesovickach 2, 180 00 Prague 8, Czech Republic
²⁰ Institut für Theoretische Physik, Lehrstuhl IV: Weltraum und Astrophysik, Ruhr-Universität Bochum, 44780 Bochum, Germany
²¹ University of Namibia, Private Bag 13301, Windhoek, Namibia

Received: 20 December 2005
Accepted: 24 January 2006

Abstract

The Vela supernova remnant (SNR) is a complex region containing a number of sources of non-thermal radiation. The inner section of this SNR, within 2 degrees of the pulsar PSR B0833-45, has been observed by the HESS γ-ray atmospheric Cherenkov detector in 2004 and 2005. A strong signal is seen from an extended region to the south of the pulsar, within an integration region of radius around the position (, J2000.0). The excess coincides with a region of hard X-ray emission seen by the ROSAT and ASCA satellites. The observed energy spectrum of the source between 550 GeV and 65 TeV is well fit by a power law function with photon index and an exponential cutoff at an energy of TeV. The integral flux above 1 TeV is . This result is the first clear measurement of a peak in the spectral energy distribution from a VHE γ-ray source, likely related to inverse Compton emission. A fit of an Inverse Compton model to the HESS spectral energy distribution gives a total energy in non-thermal electrons of ~ erg between 5 TeV and 100 TeV, assuming a distance of 290 parsec to the pulsar. The best fit electron power law index is 2.0, with a spectral break at 67 TeV.