XMM - Newton observations reveal the X - ray counterpart of the very - high - energy γ - ray source HESS J 1640 – 465

We present X-ray observations of the as of yet unidentified very high-energy (VHE) γ-ray source HESSJ1640–465 with the aim of establishing a counterpart of this source in the keV energy range, and identifying the mechanism responsible for the VHE emission. The 21.8 ksec XMM-Newton observation of HESSJ1640– 465 in September 2005 represents a significant improvement in sensitivity and angular resolution over previous ASCA studies in this region. These new data show a hard-spectrum X-ray emitting object at the centroid of the H.E.S.S. source, within the shell of the radio Supernova Remnant (SNR) G338.3–0.0. This object is consistent with the position and flux previously measured by both ASCA and Swift-XRT but is now shown to be significantly extended. We argue that this object is very likely the counterpart to HESSJ1640–465 and that both objects may represent the Pulsar Wind Nebula of an as of yet undiscovered pulsar associated with G338.3–0.0. Subject headings: ISM: Supernova remnants, plerions – ISM: individual objects: HESSJ1640–465, G338.3–0.0, AXJ1640.7–4632, 3EGJ1639–4702 – X-rays: observations – gamma-rays: observations Kavli Institute for Astroparticle Physics and Cosmology, SLAC, CA-94025, USA Max-Planck-Institut für Kernphysik, P.O. Box 103980, 69029 Heidelberg, Germany School of Physics & Astronomy, University of Leeds, Leeds LS2 9JT, UK Landessternwarte, Universität Heidelberg, Königstuhl, 69117 Heidelberg, Germany Dublin Institute for Advanced Studies, 5 Merrion Square, Dublin 2, Ireland Stanford University, HEPL & KIPAC, Stanford, CA 94305-4085, USA February 2007 SLAC-PUB-12295 Submitted to Astrophysical Journal