University of Leicester
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Revisiting the Westerlund 2 field with the HESS telescope array

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posted on 2012-10-24, 09:06 authored by A. Abramowski, F. Acero, F. Aharonian, A. G. Akhperjanian, G. Anton, A. Barnacka, de Almeida UB, A. R. Bazer-Bachi, Y. Becherini, J. Becker, B. Behera, A. Djannati-Atai, W. Domainko, B. Glueck, L. O. Drury, F. Dubois, W. Hofmann, G. Dubus, D. Khangulyan, V. Marandon, A. Fiasson, M. Raue, J. Dyks, M. Dyrda, K. Egberts, P. Eger, P. Goret, P. Espigat, D. Goering, G. Rowell, A. Foerster, G. Fontaine, S. M. Rayner, M. Fuessling, S. Gabici, M. Holleran, Y. A. Gallant, S. Hoppe, S. Schwarzburg, J. D. Hague, D. Hampf, B. Rudak, M. Hauser, M. Sikora, S. Heinz, D. Klochkov, G. Heinzelmann, W. Kluzniak, A. Szostek, D. Horns, A. Jacholkowska, S. Schwemmer, de Jager OC, M. Tluczykont, A. Reimer, C. Jahn, T. J. L. McComb, I. Jung, M. C. Medina, M. Vivier, T. Kneiske, N. Komin, P. H. Tam, K. Kosack, A. A. Zdziarski, O. Reimer, C. B. Rulten, R. Kossakowski, G. Lamanna, J. -. P. Lenain, J. Mehault, K. Bernloehr, R. Moderski, E. Moulin, H. J. Voelk, M. Naumann-Godo, O. Tibolla, J. Brucker, J. Ruppel, A. Shalchi, de Naurois M, D. Nedbal, D. Nekrassov, N. Nguyen, B. Nicholas, J. Niemiec, S. J. Nolan, M. Renaud, A. Bochow, S. Ohm, M. Ward, F. Volpe, I. Sushch, J. -. P. Tavernet, J. -. F. Olive, E. D. O. Wilhelmi, B. Opitz, K. J. Orford, S. J. Wagner, M. Ostrowski, M. Panter, M. P. Arribas, F. Ryde, G. Pedaletti, G. Pelletier, V. Borrel, C. Boisson, R. Terrier, S. Vorobiov, J. Bolmont, P. -. O. Petrucci, S. Pita, G. Puehlhofer, M. Punch, P. Bordas, A. Quirrenbach, V. Sahakian, L. Fallon, de los Reyes R, F. Rieger, J. Ripken, L. Rob, J. L. Skilton, S. Rosier-Lees, H. Sol, L. Gerard, A. Santangelo, R. Schlickeiser, C. Farnier, F. M. Schoeck, A. Schoenwald, K. Valerius, U. Schwanke, van Eldik C, G. Henri, G. Spengler, L. Stawarz, D. Gerbig, R. Steenkamp, P. Hofverberg, C. Stegmann, A. Zech, F. Stinzing, H. -. S. Zechlin, K. Katarzynski, G. Vasileiadis, C. Venter, G. Hermann, J. P. Vialle, D. Keogh, S. Fegan, A. Viana, F. Brun, P. Vincent, P. Brun, D. Lennarz, Y. Fukui, N. Furukawa, U. Katz, A. Ohama, D. Maurin, F. Feinstein, B. Giebels, H. Sano, J. Dawson, A. Kawamura, T. Bulik, I. Buesching, T. Boutelier, S. Casanova, T. Lohse, M. Cerruti, B. Khelifi, S. Kaufmann, J. F. Glicenstein, J. A. Hinton, P. M. Chadwick, A. Charbonnier, R. C. G. Chaves, A. Cheesebrough, J. Conrad, L. -. M. Chounet, A. C. Clapson, M. V. Fernandes, G. Coignet, M. Dalton, J. Masbou, C. -. C. Lu, A. Hoffmann, M. Kerschhaggl, M. K. Daniel, I. D. Davids, B. Degrange, C. Deil, A. Marcowith, H. J. Dickinson
Aims. Previous observations with the HESS telescope array revealed the existence of extended very-high-energy (VHE; E > 100 GeV) γ-ray emission, HESS J1023–575, coincident with the young stellar cluster Westerlund 2. At the time of discovery, the origin of the observed emission was not unambiguously identified, and follow-up observations have been performed to further investigate the nature of this γ-ray source. Methods. The Carina region towards the open cluster Westerlund 2 has been re-observed, increasing the total exposure to 45.9 h. The combined dataset includes 33 h of new data and now permits a search for energy-dependent morphology and detailed spectroscopy. Results. A new, hard spectrum VHE γ-ray source, HESS J1026–582, was discovered with a statistical significance of 7σ. It is positionally coincident with the Fermi LAT pulsar PSR J1028–5819. The positional coincidence and radio/γ-ray characteristics of the LAT pulsar favors a scenario where the TeV emission originates from a pulsar wind nebula. The nature of HESS J1023–575 is discussed in light of the deep HESS observations and recent multi-wavelength discoveries, including the Fermi LAT pulsar PSR J1022–5746 and giant molecular clouds in the region. Despite the improved VHE dataset, a clear identification of the object responsible for the VHE emission from HESS J1023–575 is not yet possible, and contribution from the nearby high-energy pulsar and/or the open cluster remains a possibility.



Astronomy & Astrophysics, 2011, 525


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