XMM-Newton observations of HESS J1813-178 reveal a composite Supernova remnant

¹ Max-Planck-Institut für Kernphysik, PO Box 103980, 69029 Heidelberg, Germany
² Kavli Institute for Astroparticle Physics and Cosmology, SLAC, PO Box 0029, 94025, USA e-mail: Stefan.Funk@slac.stanford.edu
³ School of Physics & Astronomy, University of Leeds, Leeds LS2 9JT, UK
⁴ Department of Astrophysics, Nagoya University, Chikusa-ku, Nagoya 464-8602, Japan
⁵ Dublin Institute for Advanced Studies, 5 Merrion Square, Dublin 2, Ireland
⁶ Institut für Astronomie und Astrophysik, Universität Tübingen, Sand 1, 72076 Tübingen, Germany
⁷ Landessternwarte, Universität Heidelberg, Königstuhl, 69117 Heidelberg, Germany
⁸ Stanford University, HEPL & KIPAC, Stanford, CA 94305-4085, USA
⁹ School of Chemistry & Physics, University of Adelaide, Adelaide 5005, Australia
¹⁰ APC, 11 Place Marcelin Berthelot, 75231 Paris Cedex 05, France
¹¹ Astronomical Institute, University Utrecht, PO Box 80000, 3508TA Utrecht, The Netherlands

Received: 20 November 2006
Accepted: 2 April 2007

Abstract

Aims.We present X-ray and ¹²CO() observations of the very-high-energy (VHE) γ-ray source HESS J1813-178 with the aim of understanding the origin of the γ-ray emission.

Methods. High-angular resolution X-ray studies of the VHE γ-ray emission region are performed using 18.6 ks of XMM-Newton data, taken on HESS J1813-178 in October 2005. Using this data set we are able to undertake spectral and morphological studies of the X-ray emission from this object with greater precision than previous studies. NANTEN ¹²CO() data are used to search for correlations of the γ-ray emission with molecular clouds which could act as target material for γ-ray production in a hadronic scenario.

Results.The NANTEN ¹²CO() observations show a giant molecular cloud of mass at a distance of 4 kpc in the vicinity of HESS J1813-178. Even though there is no direct positional coincidence, this giant cloud may have influenced the evolution of the γ-ray source and its surroundings. The X-ray data show a highly absorbed ( cm^-2) non-thermal X-ray emitting object coincident with the previously known ASCA source AX J1813–178 exhibiting a compact core and an extended tail towards the north-east, located in the centre of the radio shell-type Supernova remnant (SNR) G12.82–0.02. This central object shows morphological and spectral resemblance to a Pulsar Wind Nebula (PWN) and we therefore consider that this object is very likely to be a composite SNR. We discuss the scenario in which the γ-rays originate in the shell of the SNR, and that in which they originate in the central object, in terms of a time-dependent one-zone leptonic model. We demonstrate, that in order to connect the core X-ray emission to the VHE γ-ray emission electrons have to be accelerated to energies of at least 1 PeV.