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

Free access article

Issue		A&A Volume 448, Number 2, March III 2006


Page(s)		L43 - L47
Section		Letters
DOI		http://dx.doi.org/10.1051/0004-6361:200600014

A&A 448, L43-L47 (2006)
DOI: 10.1051/0004-6361:200600014

Letter

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

F. Aharonian¹, A. G. Akhperjanian², A. R. Bazer-Bachi³, M. Beilicke⁴, W. Benbow¹, D. Berge¹, K. Bernlöhr^{1, 5}, C. Boisson⁶, O. Bolz¹, V. Borrel³, I. Braun¹, F. Breitling⁵, A. M. Brown⁷, R. Bühler¹, I. Büsching⁸, S. Carrigan¹, P. M. Chadwick⁷, L.-M. Chounet⁹, R. Cornils⁴, L. Costamante^{1, 10}, B. Degrange⁹, H. J. Dickinson⁷, A. Djannati-Ataï¹¹, L. O'C. Drury¹², G. Dubus⁹, K. Egberts¹, D. Emmanoulopoulos¹³, B. Epinat¹⁴, P. Espigat¹¹, F. Feinstein¹⁴, E. Ferrero¹³, G. Fontaine⁹, Seb. Funk⁵, S. Funk¹, Y. A. Gallant¹⁴, B. Giebels⁹, J. F. Glicenstein¹⁵, P. Goret¹⁵, C. Hadjichristidis⁷, D. Hauser¹, M. Hauser¹³, G. Heinzelmann⁴, G. Henri¹⁶, G. Hermann¹, J. A. Hinton^{1, 13}, W. Hofmann¹, M. Holleran⁸, D. Horns¹⁷, A. Jacholkowska¹⁴, O. C. de Jager⁸, B. Khélifi^{9, 1}, Nu. Komin⁵, A. Konopelko⁵, I. J. Latham⁷, R. Le Gallou⁷, A. Lemière¹¹, M. Lemoine-Goumard⁹, T. Lohse⁵, J. M. Martin⁶, O. Martineau-Huynh¹⁸, A. Marcowith³, C. Masterson^{1, 10}, T. J. L. McComb⁷, M. de Naurois¹⁸, D. Nedbal¹⁹, S. J. Nolan⁷, A. Noutsos⁷, K. J. Orford⁷, J. L. Osborne⁷, M. Ouchrif^{18, 10}, M. Panter¹, G. Pelletier¹⁶, S. Pita¹¹, G. Pühlhofer¹³, M. Punch¹¹, B. C. Raubenheimer⁸, M. Raue⁴, S. M. Rayner⁷, A. Reimer²⁰, O. Reimer²⁰, J. Ripken⁴, L. Rob¹⁹, L. Rolland¹⁵, G. Rowell¹, V. Sahakian², L. Saugé¹⁶, S. Schlenker⁵, R. Schlickeiser²⁰, U. Schwanke⁵, H. Sol⁶, D. Spangler⁷, F. Spanier²⁰, R. Steenkamp²¹, C. Stegmann⁵, G. Superina⁹, J.-P. Tavernet¹⁸, R. Terrier¹¹, C. G. Théoret¹¹, M. Tluczykont^{9, 10}, C. van Eldik¹, G. Vasileiadis¹⁴, C. Venter⁸, P. Vincent¹⁸, H. J. Völk¹, S. J. Wagner¹³ and M. Ward⁷

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 $\gamma$ -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 $0.8\ensuremath{^{\circ}}$ around the position ( $\rm\alpha = 08^{h} 35^{m} 00^{s}$ , $\delta = -45\ensuremath{^{\circ}} 36\arcmin$ 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 $\Gamma = 1.45 \pm 0.09\ensuremath{_{{\rm stat}}}\ \pm 0.2\ensuremath{_{{\rm sys}}}$ and an exponential cutoff at an energy of $13.8 \pm 2.3\ensuremath{_{{\rm stat}}}\ \pm 4.1\ensuremath{_{{\rm sys}}}$ TeV. The integral flux above 1 TeV is $(1.28 \pm 0.17\ensuremath{_{{\rm stat}}}\ \pm 0.38\ensuremath{_{{\rm sys}}} ) \times 10^{-11}\ \ensuremath{{\rm cm}^{-2}\,{\rm s}^{-1}}$ . This result is the first clear measurement of a peak in the spectral energy distribution from a VHE $\gamma$ -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 ~ $2 \times 10^{45}$ 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.

Key words: ISM: plerions, Gamma rays: observations

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