Discovery of VHE emission towards the Carina arm region with the H.E.S.S. telescope array: HESS J1018–589

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
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, Armenia
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
e-mail: emma@mpi-hd.mpg.de
¹⁰ 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) e-mail: rterrier@apc.univ-paris7.fr
¹¹ Laboratoire Leprince-Ringuet, École Polytechnique, CNRS/IN2P3, 91128 Palaiseau, France
¹² Institut für Theoretische Physik, Lehrstuhl IV: Weltraum und Astrophysik, Ruhr-Universität Bochum, 44780 Bochum, Germany
¹³ Institut für Physik, Humboldt-Universität zu Berlin, Newtonstr. 15, 12489 Berlin, Germany
¹⁴ LUTH, Observatoire de Paris, CNRS, Université Paris Diderot, 5 Place Jules Janssen, 92190 Meudon, France
¹⁵ LPNHE, Université Pierre et Marie Curie Paris 6, Université Denis Diderot Paris 7, CNRS/IN2P3, 4 Place Jussieu, 75252 Paris Cedex 5, France
¹⁶ Institut für Astronomie und Astrophysik, Universität Tübingen, Sand 1, 72076 Tübingen, Germany
¹⁷ Astronomical Observatory, The University of Warsaw, Al. Ujazdowskie 4, 00-478 Warsaw, Poland
¹⁸ Unit for Space Physics, North-West University, Potchefstroom 2520, South Africa
¹⁹ University of Durham, Department of Physics, South Road, Durham DH1 3LE, UK
²⁰ Landessternwarte, Universität Heidelberg, Königstuhl, 69117 Heidelberg, Germany
²¹ Oskar Klein Centre, Department of Physics, Stockholm University, Albanova University Center, 10691 Stockholm, Sweden
²² University of Namibia, Department of Physics, Private Bag 13301, Windhoek, Namibia
²³ Laboratoire d’Astrophysique de Grenoble, INSU/CNRS, Université Joseph Fourier, BP 53, 38041 Grenoble Cedex 9, France
²⁴ Department of Physics and Astronomy, The University of Leicester, University Road, Leicester, LE1 7RH, UK
²⁵ Instytut Fizyki Ja¸drowej PAN, ul. Radzikowskiego 152, 31-342 Kraków, Poland
²⁶ Institut für Astro- und Teilchenphysik, Leopold-Franzens-Universität Innsbruck, 6020 Innsbruck, Austria
²⁷ Laboratoire d’Annecy-le-Vieux de Physique des Particules, Université de Savoie, CNRS/IN2P3, 74941 Annecy-le-Vieux, France
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  

Received: 18 January 2012
Accepted: 8 March 2012

Abstract

The Carina arm region, containing the supernova remnant SNR G284.3–1.8, the high-energy (HE; E > 100 MeV) binary 1FGL J1018.6–5856 and the energetic pulsar PSR J1016–5857 and its nebula, has been observed with the H.E.S.S. telescope array. The observational coverage of the region in very-high-energy (VHE; E > 0.1 TeV) γ-rays benefits from deep exposure (40 h) of the neighboring open cluster Westerlund 2. The observations have revealed a new extended region of VHE γ-ray emission. The new VHE source HESS J1018–589 shows a bright, point-like emission region positionally coincident with SNR G284.3–1.8 and 1FGL J1018.6–5856 and a diffuse extension towards the direction of PSR J1016–5857. A soft (Γ = 2.7 ± 0.5_stat) photon index, with a differential flux at 1 TeV of N₀ = (4.2 ± 1.1) × 10^-13 TeV^-1 cm^-2 s^-1 is found for the point-like source, whereas the total emission region including the diffuse emission region is well fit by a power-law function with spectral index Γ = 2.9 ± 0.4_stat and differential flux at 1 TeV of N₀ = (6.8 ± 1.6) × 10^-13 TeV^-1 cm^-2 s^-1. This H.E.S.S. detection motivated follow-up X-ray observations with the XMM-Newton satellite to investigate the origin of the VHE emission. The analysis of the XMM-Newton data resulted in the discovery of a bright, non-thermal point-like source (XMMU J101855.4–58564) with a photon index of Γ = 1.65 ± 0.08 in the center of SNR G284.3–1.8, and a thermal, extended emission region coincident with its bright northern filament. The characteristics of this thermal emission are used to estimate the plasma density in the region as n ≈ 0.5 cm^-3 (2.9 kpc/d)². The position of XMMU J101855.4–58564 is compatible with the position reported by the Fermi-LAT collaboration for the binary system 1FGL J1018.6–5856 and the variable Swift XRT source identified with it. The new X-ray data are used alongside archival multi-wavelength data to investigate the relationship between the VHE γ-ray emission from HESS J1018–589 and the various potential counterparts in the Carina arm region.