The nature of the X-ray halo of the plerion G21.5–0.9 unveiled by XMM-Newton and ChandraF. Bocchino, E. van der Swaluw, R. Chevalier and R. BandieraA&A, 442 2 (2005) 539-548DOI: https://doi.org/10.1051/0004-6361:20052870
