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 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)vpropEm 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.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- July 2014
- DOI:
- 10.1088/0004-637X/789/1/72
- arXiv:
- arXiv:1405.3239
- Bibcode:
- 2014ApJ...789...72N
- Keywords:
-
- ISM: individual objects: G21.5–0.9;
- ISM: supernova remnants;
- radiation mechanisms: general;
- stars: neutron;
- X-rays: ISM;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- 13 pages, 8 figures, 1 table, Accepted for publication in the Astrophysical Journal