The nature of the X-ray halo of the plerion G21.5–0.9 unveiled by XMM-Newton and Chandra

¹ INAF – Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, 90134 Palermo, Italy e-mail: bocchino@astropa.unipa.it
² FOM – Institute for Plasma Physics Rijnhuizen, PO Box 1207, 3430 BE Nieuwegein, The Netherlands
³ School of Physics and Astronomy, The University of Leeds, Woodhouse Lane, Leeds LS2 9JT, UK
⁴ Department of Astronomy, University of Virginia, PO Box 3818, Charlottesville, VA 22903, USA
⁵ INAF – Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy

Received: 11 February 2005
Accepted: 15 July 2005

Abstract

The nature of the radio-quiet X-ray halo around the plerionic supernova remnant G21.5-0.9  is under debate. On the basis of spatial and spectral analysis of a large Chandra  and XMM-Newton  dataset of this source, we have developed a self-consistent scenario which explains all the observational features. We found that the halo is composed by diffuse extended emission due to dust scattering of X-rays from the plerion, by a bright limb which traces particle acceleration in the fast forward shock of the remnant, and by a bright spot (the “North Spur”) which may be a knot of ejecta in adiabatic expansion. By applying a model of interaction between the PWN, the remnant and the supernova environment, we argue that G21.5-0.9  progenitor may be of Type IIP or Ib/Ic, and that the remnant may be young (200–1000 yr).