Discovery of the source HESS J1356-645 associated with the young and energetic PSR J1357-6429

¹ Universität Hamburg, Institut für Experimentalphysik, Luruper Chaussee 149, 22761 Hamburg, Germany
² Laboratoire Univers et Particules de Montpellier, Université Montpellier 2, CNRS/IN2P3, CC 72, Place Eugène Bataillon, 34095 Montpellier Cedex 5, France
e-mail: mrenaud@lupm.univ-montp2.fr; facero@in2p3.fr
³ Max-Planck-Institut für Kernphysik, PO Box 103980, 69029 Heidelberg, Germany
⁴ Dublin Institute for Advanced Studies, 31 Fitzwilliam Place, Dublin 2, Ireland
⁵ National Academy of Sciences of the Republic of Armenia, Yerevan
⁶ Yerevan Physics Institute, 2 Alikhanian Brothers St., 375036 Yerevan, Armenia
⁷ Universität Erlangen-Nürnberg, Physikalisches Institut, Erwin-Rommel-Str. 1, 91058 Erlangen, Germany
⁸ Nicolaus Copernicus Astronomical Center, ul. Bartycka 18, 00-716 Warsaw, Poland
⁹ CEA Saclay, DSM/IRFU, 91191 Gif-Sur-Yvette Cedex, France
¹⁰ University of Durham, Department of Physics, South Road, Durham DH1 3LE, UK
¹¹ Astroparticule et Cosmologie (APC), CNRS, Université Paris 7 Denis Diderot, 10 rue Alice Domon et Léonie Duquet, 75205 Paris Cedex 13, France (UMR 7164: CNRS, Université Paris VII, CEA, Observatoire de Paris )
¹² Laboratoire Leprince-Ringuet, École Polytechnique, CNRS/IN2P3, 91128 Palaiseau, France
¹³ Institut für Theoretische Physik, Lehrstuhl IV: Weltraum und Astrophysik, Ruhr-Universität Bochum, 44780 Bochum, Germany
¹⁴ Landessternwarte, Universität Heidelberg, Königstuhl, 69117 Heidelberg, Germany
¹⁵ Institut für Physik, Humboldt-Universität zu Berlin, Newtonstr. 15, 12489 Berlin, Germany
¹⁶ LUTH, Observatoire de Paris, CNRS, Université Paris Diderot, 5 place Jules Janssen, 92190 Meudon, France
¹⁷ LPNHE, Université Pierre et Marie Curie Paris 6, Université Denis Diderot Paris 7, CNRS/IN2P3, 4 place Jussieu, 75252, Paris Cedex 5, France
¹⁸ Institut für Astronomie und Astrophysik, Universität Tübingen, Sand 1, 72076 Tübingen, Germany
¹⁹ Astronomical Observatory, The University of Warsaw, Al. Ujazdowskie 4, 00-478 Warsaw, Poland
²⁰ Unit for Space Physics,North-West University, Potchefstroom 2520, South Africa
²¹ Laboratoire d’Annecy-le-Vieux de Physique des Particules, Université de Savoie, CNRS/IN2P3, 74941 Annecy-le-Vieux, France
²² Oskar Klein Centre, Department of Physics, Stockholm University, Albanova University Center, 10691 Stockholm, Sweden
²³ University of Namibia, Department of Physics, Private Bag 13301, Windhoek, Namibia
²⁴ Laboratoire d’Astrophysique de Grenoble, INSU/CNRS, Université Joseph Fourier, BP 53, 38041 Grenoble Cedex 9, France
²⁵ Department of Physics and Astronomy, The University of Leicester, University Road, Leicester, LE1 7RH, UK
²⁶ Instytut Fizyki Ja¸drowej PAN, ul. Radzikowskiego 152, 31-342 Kraków, Poland
²⁷ Institut für Astro- und Teilchenphysik, Leopold-Franzens-Universität Innsbruck, 6020 Innsbruck, Austria
²⁸ Obserwatorium Astronomiczne, Uniwersytet Jagielloński, ul. Orla 171, 30-244 Kraków, Poland
²⁹ Toruń Centre for Astronomy, Nicolaus Copernicus University, ul. Gagarina 11, 87-100 Toruń, Poland
³⁰ School of Chemistry & Physics, University of Adelaide, Adelaide 5005, Australia
³¹ Charles University, Faculty of Mathematics and Physics, Institute of Particle and Nuclear Physics, V Holešovičkách 2, 180 00 Prague 8, Czech Republic
³² School of Physics & Astronomy, University of Leeds, Leeds LS2 9JT, UK
³³ European Associated Laboratory for Gamma-Ray Astronomy, jointly supported by CNRS and MPG, France

Received: 9 June 2011
Accepted: 8 August 2011

Abstract

Context. Several newly discovered very-high-energy (VHE; E  >  100 GeV) γ-ray sources in the Galaxy are thought to be associated with energetic pulsars. Among them, middle-aged (≳ 10⁴ yr) systems exhibit large centre-filled VHE nebulae, offset from the pulsar position, which result from the complex relationship between the pulsar wind and the surrounding medium, and reflect the past evolution of the pulsar.

Aims. Imaging Atmospheric Cherenkov Telescopes (IACTs) have been successful in revealing extended emission from these sources in the VHE regime. Together with radio and X-ray observations, this observational window allows one to probe the energetics and magnetic field inside these large-scale nebulae.

Methods. H.E.S.S., with its large field of view, angular resolution of  ≲0.1° and unprecedented sensitivity, has been used to discover a large population of such VHE sources. In this paper, the H.E.S.S. data from the continuation of the Galactic Plane Survey (− 80°  <  ℓ  <  60°, |b|  <  3°), together with the existing multi-wavelength observations, are used.

Results. A new VHE γ-ray source was discovered at RA (J2000) = 13^h56^m00^s, Dec (J2000) = −64°30′00′′ with a 2′ statistical error in each coordinate, namely HESS J1356−645. The source is extended, with an intrinsic Gaussian width of (0.20  ±  0.02)°. Its integrated energy flux between 1 and 10 TeV of 8  ×  10^-12 erg cm^-2 s^-1 represents  ~11% of the Crab Nebula flux in the same energy band. The energy spectrum between 1 and 20 TeV is well described by a power law dN/dE  ∝  E^−Γ with photon index Γ = 2.2  ±  0.2_stat  ±  0.2_sys. The inspection of archival radio images at three frequencies and the analysis of X-ray data from ROSAT/PSPC and XMM-Newton/MOS reveal the presence of faint non-thermal diffuse emission coincident with HESS J1356−645.

Conclusions. HESS J1356−645 is most likely associated with the young and energetic pulsar PSR J1357−6429 (d = 2.4 kpc, τ_c = 7.3 kyr and Ė = 3.1  ×  10³⁶ erg s^-1), located at a projected distance of  ~5 pc from the centroid of the VHE emission. HESS J1356−645 and its radio and X-ray counterparts would thus represent the nebula resulting from the past history of the PSR J1357−6429 wind. In a simple one-zone model,