Discovery of the hard spectrum VHE gamma-ray source HESS J1641-463

A. Abramowski , F. Aharonian , F. Ait Benkhali , A. G. Akhperjanian , E. O. Angüner , M. Backes , S. Balenderan , Agnès Balzer , A. Barnacka , Y. Becherini , J. Becker Tjus , D. Berge , S. Bernhard , K. Bernlöhr , E. Birsin , J. Biteau (1) , M. Böttcher , C. Boisson (2) , J. Bolmont (3) , P. Bordas , J. Bregeon , F. Brun , P. Brun (4) , M. Bryan , T. Bulik , S. Carrigan , S. Casanova , P. M. Chadwick , N. Chakraborty , R. Chalme-Calvet (3) , R. C. G. Chaves , M. Chrétien (3) , S. Colafrancesco , G. Cologna , J. Conrad , C. Couturier (3) , Y. Cui , I. D. Davids , B. Degrange (1) , C. Deil , P. Dewilt , A. Djannati-Ataï (5) , W. Domainko , A. Donath , L. O'C. Drury , G. Dubus , K. Dutson , J. Dyks , M. Dyrda , T. Edwards , K. Egberts , P. Eger , P. Espigat (5) , C. Farnier , S. Fegan (1) , F. Feinstein (6) , M. V. Fernandes , D. Fernandez (6) , A. Fiasson (7) , G. Fontaine (1) , A. Förster , M. Füssling , S. Gabici (5) , M. Gajdus , Y. A. Gallant (6) , T. Garrigoux (3) , G. Giavitto , B. Giebels (1) , J. F. Glicenstein , D. Gottschall , M. -H. Grondin , M. Grudzińska , D. Hadasch , S. Häffner , J. Hahn , J. Harris , G. Heinzelmann , G. Henri , G. Hermann , O. Hervet (2) , A. Hillert , J. A. Hinton , W. Hofmann , P. Hofverberg , M. Holler , D. Horns , A. Ivascenko , A. Jacholkowska (3) , C. Jahn , M. Jamrozy , M. Janiak , F. Jankowsky , I. Jung-Richardt , M. A. Kastendieck , K. Katarzyński , U. Katz , S. Kaufmann , B. Khélifi (1, 5) , Michel Kieffer (3) , S. Klepser , D. Klochkov , W. Kluźniak , D. Kolitzus , Nu. Komin (7) , K. Kosack , S. Krakau , F. Krayzel (7) , P. P. Krüger , H. Laffon (8) , G. Lamanna (7) , J. Lau , J. Lefaucheur (5) , V. Lefranc , A. Lemière (5) , M. Lemoine-Goumard (8) , J. -P. Lenain (3) , T. Lohse , A. Lopatin , C. -C. Lu , V. Marandon , Alexandre Marcowith (6) , R. Marx , G. Maurin (7) , N. Maxted , M. Mayer , T. J. L. Mccomb , J. Méhault (6) , P. J. Meintjes , U. Menzler , M. Meyer , A. M. W. Mitchell , R. Moderski , M. Mohamed , K. Morå , Emmanuel Moulin , T. Murach , M. de Naurois (1) , J. Niemiec , S. J. Nolan , L. Oakes , H. Odaka , S. Ohm , B. Opitz , M. Ostrowski , I. Oya , M. Panter , R. D. Parsons , M. Paz Arribas , N. W. Pekeur , G. Pelletier , P. -O. Petrucci , B. Peyaud , S. Pita (5) , H. Poon , G. Pühlhofer , M. Punch (5) , A. Quirrenbach , S. Raab , I. Reichardt (5) , A. Reimer , O. Reimer , Matthieu Renaud (6) , R. de Los Reyes , F. Rieger , C. Romoli , S. Rosier-Lees (7) , G. Rowell , B. Rudak , C. B. Rulten (2) , V. Sahakian , D. Salek , D. A. Sanchez (7) , A. Santangelo , R. Schlickeiser , F. Schüssler , A. Schulz , U. Schwanke , S. Schwarzburg , S. Schwemmer , H. Sol (2) , F. Spanier , G. Spengler , F. Spies , {ł. } Stawarz , R. Steenkamp , C. Stegmann , F. Stinzing , K. Stycz , I. Sushch , J. -P. Tavernet (3) , T. Tavernier (5) , A. M. Taylor , R. Terrier (5) , M. Tluczykont , C. Trichard (7) , K. Valerius , C. van Eldik , B. van Soelen , George Vasileiadis (6) , J. Veh , C. Venter , A. Viana , P. Vincent (3) , J. Vink , H. J. Völk , F. Volpe , M. Vorster , T. Vuillaume , S. J. Wagner , P. Wagner , R. M. Wagner , M. Ward , M. Weidinger , Q. Weitzel , R. White , A. Wierzcholska , P. Willmann , A. Wörnlein , D. Wouters , R. Yang , V. Zabalza , D. Zaborov , M. Zacharias , A. A. Zdziarski , A. Zech (2) , H. -S. Zechlin , Y. Fukui , H. Sano , T. Fukuda , S. Yoshiike

1 LLR - Laboratoire Leprince-Ringuet
2 LUTH (UMR_8102) - Laboratoire Univers et Théories
3 LPNHE - Laboratoire de Physique Nucléaire et de Hautes Énergies
4 IRFU - Institut de Recherches sur les lois Fondamentales de l'Univers
5 APC (UMR_7164) - AstroParticule et Cosmologie
6 LUPM - Laboratoire Univers et Particules de Montpellier
7 LAPP - Laboratoire d'Annecy de Physique des Particules
8 ASTRO - Astroparticules

This letter reports the discovery of a remarkably hard spectrum source, HESS J1641-463, by the High Energy Stereoscopic System (H.E.S.S.) in the very-high energy (VHE) domain. HESS J1641-463 remained unnoticed by the usual analysis techniques due to confusion with the bright nearby source HESS J1640-465. It emerged at a significance level of 8.5 standard deviations after restricting the analysis to events with energies above 4 TeV. It shows a moderate flux level of F(E > 1 TeV) = (3.64 +/- 0.44_stat +/- 0.73_sys) x 10^-13 cm^-2s-1, corresponding to 1.8% of the Crab Nebula flux above the same energy, and a hard spectrum with a photon index of Gamma = 2.07 +/- 0.11_stat +/- 0.20_sys. It is a point-like source, although an extension up to Gaussian width of sigma = 0.05 deg cannot be discounted due to uncertainties in the H.E.S.S. PSF. The VHE gamma-ray flux of HESS J1641-463 is found to be constant over the observed period when checking time binnings from year-by-year to the 28 min exposures timescales. HESS J1641-463 is positionally coincident with the radio supernova remnant SNR G338.5+0.1. No X-ray candidate stands out as a clear association, however Chandra and XMM-Newton data reveal some potential weak counterparts. Various VHE gamma-ray production scenarios are discussed. If the emission from HESS J1641-463 is produced by cosmic ray protons colliding with the ambient gas, then their spectrum must extend up to at least a few hundred TeV. The energy released in accelerating these particles could account for the entire energy budget of the galactic cosmic ray population above a few TeV.

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

A. Abramowski, F. Aharonian, F. Ait Benkhali, A. G. Akhperjanian, E. O. Angüner, et al.. Discovery of the hard spectrum VHE gamma-ray source HESS J1641-463. The Astrophysical journal letters, 2014, 794 (1), pp.L1. ⟨10.1088/2041-8205/794/1/L1⟩. ⟨in2p3-01061876⟩