Revisiting the Westerlund 2 Field with the H.E.S.S. Telescope Array

A. Abramowski , Fabio Acero (1) , F. Aharonian , A. G. Akhperjanian , G. Anton , A. Barnacka , U. Barres de Almeida , A. R. Bazer-Bachi (2) , Y. Becherini (3) , J. Becker , B. Behera , K. Bernlöhr , A. Bochow , C. Boisson (4) , J. Bolmont (5) , P. Bordas , V. Borrel (2) , J. Brucker , F. Brun (5) , P. Brun (6) , T. Bulik , I. Büsching , T. Boutelier (7) , S. Casanova , M. Cerruti (4) , P. M. Chadwick , A. Charbonnier (5) , R. C. G. Chaves , A. Cheesebrough , J. Conrad , L. -M. Chounet (8) , A. C. Clapson , G. Coignet (9) , M. Dalton , M. K. Daniel , I. D. Davids , B. Degrange (8) , C. Deil , H. J. Dickinson , A. Djannati-Ataï (10) , W. Domainko , L. O'C. Drury , F. Dubois (9) , G. Dubus (7) , J. Dyks , M. Dyrda , K. Egberts , P. Eger , P. Espigat (3) , L. Fallon , C. Farnier (1) , S. Fegan (8) , F. Feinstein (1) , M. V. Fernandes , A. Fiasson (9) , A. Förster , G. Fontaine (8) , M. Füssling , S. Gabici (2) , Y. A. Gallant (1) , L. Gérard (3) , D. Gerbig , B. Giebels (8) , J. F. Glicenstein (6) , B. Glück , P. Goret (6) , D. Göring , J. D. Hague , D. Hampf , M. Hauser , S. Heinz , G. Heinzelmann , G. Henri (7) , G. Hermann , J. A. Hinton , A. Hoffmann , W. Hofmann , P. Hofverberg , M. Holleran , S. Hoppe , D. Horns , A. Jacholkowska (5) , O. C. de Jager , C. Jahn , I. Jung , K. Katarzyński , U. Katz , S. Kaufmann , M. Kerschhaggl , D. Khangulyan , B. Khélifi (8) , D. Keogh , D. Klochkov , W. Kluźniak24 , T. Kneiske , Nu. Komin (9) , K. Kosack (6) , R. Kossakowski (9) , G. Lamanna (9) , J. -P. Lenain (4) , D. Lennarz , T. Lohse , C. -C. Lu , V. Marandon (3) , A. Marcowith (1) , Julien Masbou (9) , D. Maurin (5) , T. J. L. Mccomb , M. C. Medina , J. Méhault (1) , R. Moderski , Emmanuel Moulin (6) , M. Naumann-Godo , M. de Naurois (5) , D. Nedbal , D. Nekrassov , N. Nguyen , B. Nicholas , J. Niemiec , S. J. Nolan , S. Ohm , J-F. Olive (2) , E. de Oña Wilhelmi , B. Opitz , K. J. Orford , M. Ostrowski , M. Panter , M. Paz Arribas , G. Pedaletti , G. Pelletier (7) , P. -O. Petrucci (7) , S. Pita (10) , G. Pühlhofer , M. Punch (10) , A. Quirrenbach , M. Raue , S. M. Rayner , A. Reimer , O. Reimer , M. Renaud (3) , R. de Los Reyes , F. Rieger , J. Ripken , L. Rob (8) , S. Rosier-Lees (9) , G. Rowell , B. Rudak , C. B. Rulten , J. Ruppel , F. Ryde , V. Sahakian , A. Santangelo , R. Schlickeiser , F. M. Schöck , A. Schönwald , U. Schwanke , S. Schwarzburg , S. Schwemmer , A. Shalchi , I. Sushch , M. Sikora , J. L. Skilton , H. Sol (4) , G. Spengler , Ł. Stawarz , R. Steenkamp , C. Stegmann , F. Stinzing , A. Szostek (7) , P. H. Tam , J. -P. Tavernet (5) , R. Terrier (10) , O. Tibolla , M. Tluczykont (2, 8) , K. Valerius , C. van Eldik , G. Vasileiadis (1) , C. Venter , J. P. Vialle (9) , A. Viana , P. Vincent (5) , M. Vivier (6) , H. J. Völk , F. Volpe (8) , S. Vorobiov (1) , S. J. Wagner , M. Ward , A. A. Zdziarski , A. Zech (4) , H. -S. Zechlin , Y. Fukui , N. Furukawa , A. Ohama , H. Sano , J. Dawson , A. Kawamura

1 LPTA - Laboratoire de Physique Théorique et Astroparticules
2 CESR - Centre d'étude spatiale des rayonnements
3 APC (UMR_7164) - AstroParticule et Cosmologie
4 LUTH (UMR_8102) - Laboratoire Univers et Théories
5 LPNHE - Laboratoire de Physique Nucléaire et de Hautes Énergies
6 IRFU - Institut de Recherches sur les lois Fondamentales de l'Univers
7 IPAG - Institut de Planétologie et d'Astrophysique de Grenoble
8 LLR - Laboratoire Leprince-Ringuet
9 LAPP - Laboratoire d'Annecy de Physique des Particules
10 APC - AHE - APC - Astrophysique des Hautes Energies

Aims. Previous observations with the H.E.S.S. telescope array revealed the existence of extended very-high-energy (VHE; E>100 GeV) {\gamma}-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 {\gamma}-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 {\gamma}-ray source, HESSJ1026-582, was discovered with a statistical significance of 7{\sigma}. It is positionally coincident with the Fermi LAT pulsar PSR J1028-5819. The positional coincidence and radio/{\gamma}-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 H.E.S.S. observations and recent multi-wavelength discoveries, including the Fermi LAT pulsar PSRJ1022-5746 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.

Mots clés: ISM: HII regions; ISM: individual objects: HESS J1023-575; Gamma-ray: stars; HESS J1026-582; RCW 49 (NGC 3247; G284.3-0.3); PSRJ1028-5819; PSRJ1022-5746

Domaines: Phénomènes cosmiques de haute energie [astro-ph.HE]; Phénomènes cosmiques de haute energie [astro-ph.HE]

A. Abramowski, Fabio Acero, F. Aharonian, A. G. Akhperjanian, G. Anton, et al.. Revisiting the Westerlund 2 Field with the H.E.S.S. Telescope Array. Astronomy and Astrophysics - A&A, 2011, 525, pp.A46. ⟨10.1051/0004-6361/201015290⟩. ⟨in2p3-00519435⟩