title: Chandra Observations of the Crab-like Supernova Remnant G21.5-0.9.
abstract: Chandra observations of the Crab-like supernova remnant G21.5-0.9 reveal a compact central core and spectral variations indicative of synchrotron burn-off of higher energy electrons in the inner nebula. The central core is slightly extended, perhaps indicating the presence of an inner wind-shock nebula surrounding the pulsar. No pulsations are observed from the central region, yielding an upper limit of approximately 40% for the pulsed fraction. A faint outer shell may be the first evidence of the expanding ejecta and blast wave formed in the initial explosion, indicating a composite nature for G21.5-0.9.
authors.initials: P
authors.lastname: Slane
authors.initials: Y
authors.lastname: Chen
authors.initials: NS
authors.lastname: Schulz
authors.initials: FD
authors.lastname: Seward
authors.initials: JP
authors.lastname: Hughes
authors.initials: BM
authors.lastname: Gaensler