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

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posted on 24.10.2012, 09:09 by F. Aharonian, W. Benbow, D. Berge, K. Bernlöhr, O. Bolz, I. Braun, R. Bühler, S. Carrigan, L. Costamante, K. Egberts, S. Funk, C. Masterson, M. Ouchrif, M. Tluczykont, G. Hermann, J. A. Hinton, W. Hofmann, B. Khélifi, M. Panter, G. Rowell, V. Sahakian, van Eldik C, H. J. Völk, A. G. Akhperjanian, A. R. Bazer-Bachi, V. Borrel, A. Marcowith, M. Beilicke, R. Cornils, G. Heinzelmann, M. Raue, J. Ripken, A. Konopelko, F. Breitling, N. Komin, T. Lohse, S. Schlenker, U. Schwanke, C. Stegmann, C. Boisson, J. M. Martin, H. Sol, A. M. Brown, P. M. Chadwick, le Gallou R, H. J. Dickinson, C. Hadjichristidis, I. J. Latham, T. J. L. McComb, S. J. Nolan, A. Noutsos, K. J. Orford, J. L. Osborne, S. M. Rayner, D. Spangler, M. Ward, I. Büsching, C. Venter, M. Holleran, de Jager OC, B. C. Raubenheimer, L. -. M. Chounet, B. Degrange, G. Dubus, G. Fontaine, B. Giebels, M. Lemoine-Goumard, G. Superina, S. Pita, A. Djannati-Ataï, P. Espigat, A. Lemière, M. Punch, R. Terrier, C. G. Théoret, L. O. Drury, D. Emmanoulopoulos, E. Ferrero, M. Hauser, G. Pühlhofer, Y. A. Gallant, S. J. Wagner, B. Epinat, F. Feinstein, A. Jacholkowska, G. Vasileiadis, J. F. Glicenstein, P. Goret, L. Rolland, G. Henri, G. Pelletier, L. Saugé, D. Horns, J. -. P. Tavernet, O. Martineau-Huynh, de Naurois M, P. Vincent, D. Nedbal, L. Rob, A. Reimer, O. Reimer, R. Schlickeiser, F. Spanier, R. Steenkamp, D. Hauser
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.



Astronomy & Astrophysics, 2006, 448 (2)


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