Nynka, Melania10; Hailey, Charles J.10; Reynolds, Stephen P.4; An, Hongjun11; Baganoff, Frederick K.12; Boggs, Steven E.7; Christensen, Finn Erland1; Craig, William W.7; Gotthelf, Eric V.10; Grefenstette, Brian W.13; Harrison, Fiona A.13; Krivonos, Roman7; Madsen, Kristin K.13; Mori, Kaya10; Perez, Kerstin10; Stern, Daniel13; Wik, Daniel R.14; Zhang, William W.14; Zoglauer, Andreas7
1 National Space Institute, Technical University of Denmark2 Astrophysics, National Space Institute, Technical University of Denmark3 Columbia University4 North Carolina State University5 McGill University6 Massachusetts Institute of Technology7 University of California8 California Institute of Technology9 NASA Goddard Space Flight Center10 Columbia University11 McGill University12 Massachusetts Institute of Technology13 California Institute of Technology14 NASA Goddard Space Flight Center
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 similar 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 similar 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 similar to 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) proportional to E-m 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.