Serendipitous discovery of the unidentified extended TeV gamma-ray source HESS J1303-631

The serendipitous discovery of an unidentified extended TeV γ-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 HESS stereoscopic system of Cherenkov telescopes in Namibia. HESS J1303-631 was discovered roughly 0.6° 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 σ = (0.16 ± 0.02)° and the integral flux above 380 GeV is compatible with constant emission over the entire observational period of (17 ± 3)% of the Crab Nebula flux. The measured energy spectrum can be described by a power-law dN/dE ˜ E-Γ with a photon index of Γ = 2.44 ± 0.05stat ± 0.2syst. Up to now, no counterpart at other wavelengths is identified. Various possible TeV production scenarios are discussed.Aharonian, F., Akhperjanian, A. G., Aye, K.-M., Bazer-Bachi, A. R., Beilicke, M., Benbow, W., Berge, D., Berghaus, P., Bernlöhr, K:, Bolz, O., Boisson, C., Glicenstein, J.F., Breitling, F., Brown, A. M., Bussons Gordo, J., Chadwick, P. M., Braun, I., Chounet, L.-M., Cornils, R., Costamante, L., Degrange, B., Djannati-Atai, A., Drury, L.O'C., Emmanoulopoulos, D.; Espigat, P.; Feinstein, F.; Fleury, P., Fontaine, G., Funk, S., Gallant, Y. A., Giebels, B., Gillessen, S., Goret, P., Dubus, G., Hadjichristidis, C., Hauser, M., Heinzelmann, G., Henri, G., Hermann, G.; Hinton, J. A., Hofmann, W., Holleran, M., Horns, D., de Jager, O. C., Khélifi, B., Komin, N., Konopelko, A., Latham, I. J., Le Gallou, R., Lemoine-Goumard, M., Lemière, A., Leroy, N., Lohse, T.; Marcowith, A.; Masterson, C.; McComb, T. J. L.; de Naurois, M.; Nolan, S. J.; Noutsos, A.; Orford, K. J.; Osborne, J. L.; Ouchrif, M.; Panter, M.; Pelletier, G.; Pita, S.; Fuchs, Y.; Pühlhofer, G.; Punch, M.; Raubenheimer, B. C.; Raue, M.; Raux, J.; Rayner, S. M.; Redondo, I.; Reimer, A.; Reimer, O.; Ripken, J.; Terrier, R.; Rob, L.; Rolland, L.; Rowell, G.; Sahakian, V.; Saugé, L.; Schlenker, S.; Schlickeiser, R.; Schuster, C.; Schwanke, U.; Siewert, M.; Sol, H.; Steenkamp, R.; Stegmann, C.; Tavernet, J.-P-; Théoret, C. G., Tluczykont, M., Venter, C., Vasileiadis, G., Vincent, P.; Völk, H. J., Wagner, S. J., Martineau-Huynh, O. and van der Walt, D.J