Astrophys. J., 789, 72 (2014/July-1)
NuSTAR study of hard X-ray morphology and spectroscopy of PWN G21.5-0.9.
NYNKA M., HAILEY C.J., REYNOLDS S.P., AN H., BAGANOFF F.K., BOGGS S.E., CHRISTENSEN F.E., CRAIG W.W., GOTTHELF E.V., GREFENSTETTE B.W., HARRISON F.A., KRIVONOS R., MADSEN K.K., MORI K., PEREZ K., STERN D., WIK D.R., ZHANG W.W. and ZOGLAUER A.
Abstract (from CDS):
We present NuSTAR high-energy X-ray observations of the pulsar wind nebula (PWN)/supernova remnant G21.5-0.9. We detect integrated emission from the nebula up to ∼40 keV, and resolve individual spatial features over a broad X-ray band for the first time. The morphology seen by NuSTAR agrees well with that seen by XMM-Newton and Chandra below 10 keV. At high energies, NuSTAR clearly detects non-thermal emission up to ∼20 keV that extends along the eastern and northern rim of the supernova shell. The broadband images clearly demonstrate that X-ray emission from the North Spur and Eastern Limb results predominantly from non-thermal processes. We detect a break in the spatially integrated X-ray spectrum at ∼9 keV that cannot be reproduced by current spectral energy distribution models, implying either a more complex electron injection spectrum or an additional process such as diffusion compared to what has been considered in previous work. We use spatially resolved maps to derive an energy-dependent cooling length scale, L(E)∝Em with m = -0.21±0.01. We find this to be inconsistent with the model for the morphological evolution with energy described by Kennel & Coroniti. This value, along with the observed steepening in power-law index between radio and X-ray, can be quantitatively explained as an energy-loss spectral break in the simple scaling model of Reynolds, assuming particle advection dominates over diffusion. This interpretation requires a substantial departure from spherical magnetohydrodynamic, magnetic-flux-conserving outflow, most plausibly in the form of turbulent magnetic-field amplification.
ISM: individual: G21.5-0.9 - ISM: supernova remnants - radiation mechanisms: general - stars: neutron - X-rays: ISM
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