NuSTAR study of Hard X-Ray Morphology and Spectroscopy of PWN G21.5-0.9

Abstract

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 SED 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, $L(E)\propto E^m$ with $m=-0.21\pm 0.01$. We find this to be inconsistent with the model for the morphological evolution with energy described by Kennel & Coroniti (1984). 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 (2009), assuming particle advection dominates over diffusion. This interpretation requires a substantial departure from spherical magnetohydrodynamic (MHD), magnetic-flux-conserving outflow, most plausibly in the form of turbulent magnetic-field amplification.

13 pages, 8 figures, 1 table, Accepted for publication in the Astrophysical Journal

References in corpus (4)

• Fermi-LAT Search for Pulsar Wind Nebulae around gamma-ray Pulsars
• The Distances of SNRs Kes 69 and G21.5-0.9 from HI and 13CO Spectra
• A Shell of Thermal X-ray Emission Associated with the Young Crab-like Remnant 3C58
• X-ray Dust Scattering at Small Angles: The Complete Halo around GX13+1

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