%0 Journal Article %T Serendipitous discovery of the unidentified extended TeV gamma-ray source HESS J1303-631 %+ AstroParticule et Cosmologie (APC (UMR_7164)) %+ Laboratoire de Physique Théorique et Astroparticules (LPTA) %+ Laboratoire Leprince-Ringuet (LLR) %+ Laboratoire de Physique Nucléaire et de Hautes Énergies (LPNHE) %A Aharonian, F. %A Akhperjanian, A.G. %A Aye, K.-M. %A Bazer-Bachi, A.R. %A Beilicke, M. %A Benbow, W. %A Berge, D. %A Berghaus, P. %A Bernlohr, K. %A Boisson, C. %A Bolz, O. %A Braun, I. %A Breitling, F. %A Brown, A.M. %A Bussons Gordo, J. %A Chadwick, P.M. %A Chounet, L.-M. %A Cornils, R. %A Costamante, L. %A Degrange, B. %A Djannati-Ataï, A. %A Drury, L.O'C. %A Dubus, G. %A Emmanoulopoulos, D. %A Espigat, P. %A Feinstein, F. %A Fleury, P. %A Fontaine, G. %A Fuchs, Y. %A Funk, S. %A Gallant, Y.A. %A Giebels, B. %A Gillessen, S. %A Glicenstein, J.F. %A Goret, P. %A Hadjichristidis, C. %A Hauser, M. %A Heinzelmann, G. %A Henri, G. %A Hermann, G. %A Hinton, J.A. %A Hofmann, W. %A Holleran, M. %A Horns, D. %A de Jager, O.C. %A Khelifi, B. %A Komin, Nu. %A Konopelko, A. %A Latham, I.J. %A Le Gallou, R. %A Lemière, A. %A Lemoine-Goumard, M. %A Leroy, N. %A Lohse, T. %A Martineau-Huynh, O. %A Marcowith, A. %A Masterson, C. %A Mccomb, T.J.L. %A de Naurois, M. %A Nolan, S.J. %A Noutsos, A. %A Orford, K.J. %A Osborne, J.L. %A Ouchrif, M. %A Panter, M. %A Pelletier, G. %A Pita, S. %A Puhlhofer, G. %A Punch, M. %A Raubenheimer, B.C. %A Raue, M. %A Raux, J. %A Rayner, S.M. %A Redondo, I. %A Reimer, A. %A Reimer, O. %A Ripken, J. %A Rob, L. %A Rolland, L. %A Rowell, G. %A Sahakian, V. %A Sauge, L. %A Schlenker, S. %A Schlickeiser, R. %A Schuster, C. %A Schwanke, U. %A Siewert, M. %A Sol, H. %A Steenkamp, R. %A Stegmann, C. %A Tavernet, J.-P. %A Terrier, R. %A Théoret, C.G. %A Tluczykont, M. %A van Der Walt, D.J. %A Vasileiadis, G. %A Venter, C. %A Vincent, P. %A Volk, H.J. %A Wagner, S.J. %< avec comité de lecture %Z APC-05-21 %@ 0004-6361 %J Astronomy & Astrophysics - A&A %I EDP Sciences %V 439 %P 1013-1021 %8 2005 %D 2005 %Z astro-ph/0505219 %R 10.1051/0004-6361:20053195 %K Gamma rays: observations %K Galaxy: disk %Z Sciences of the Universe [physics]/Astrophysics [astro-ph] %Z Physics [physics]/Astrophysics [astro-ph]/Cosmology and Extra-Galactic Astrophysics [astro-ph.CO]Journal articles %X The serendipitous discovery of an unidentified extended TeV $\gamma$-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 H.E.S.S. stereoscopic system of Cherenkov telescopes in Namibia. HESS J1303-631 was discovered roughly 0.6 \degres 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 $\sigma$ = (0.16 $\pm$ 0.02)\degres and the integral flux above 380 GeV is compatible with constant emission over the entire observational period of (17$\pm$ 3)% of the Crab Nebula flux. The measured energy spectrum can be described by a power-law dN/dE $\sim$ E$^{-\Gamma}$ with a photon index of $\Gamma$ = 2.44 $\pm 0.05$_{stat} \pm$ 0.2$_{syst}$. Up to now, no counterpart at other wavelengths is identified. Various possible TeV production scenarios are discussed. %G English %Z HESS %L in2p3-00024344 %U https://in2p3.hal.science/in2p3-00024344 %~ IN2P3 %~ OBSPM %~ CEA %~ UNIV-PARIS7 %~ X %~ UPMC %~ LPTA %~ LLR %~ LPNHE %~ APC %~ CNRS %~ UNIV-MONTP2 %~ X-LLR %~ X-DEP %~ X-DEP-PHYS %~ DSM-IRFU %~ IRFU-APC %~ PSL %~ UPMC_POLE_2 %~ UNIV-MONTPELLIER %~ CEA-DRF %~ SORBONNE-UNIVERSITE %~ SU-SCIENCES %~ UNIV-PARIS %~ UP-SCIENCES %~ OBSPM-PSL %~ SU-TI %~ ALLIANCE-SU %~ UM1-UM2 %~ LPNHE-2