Acceleration of X-Ray Emitting Electrons in the Crab Nebula

Gwenael Giacinti, John G. Kirk
2018 Astrophysical Journal  
We study particle acceleration at the termination shock of a striped pulsar wind by integrating trajectories in a prescribed model of the magnetic field and flow pattern. Drift motion on the shock surface maintains either electrons or positrons on "Speiser" orbits in a ring-shaped region close to the equatorial plane of the pulsar, enabling them to be accelerated to very high energy by the first-order Fermi mechanism. A power-law spectrum results: dN_ e/dγ∝γ^α_ e, where α_ e lies in the range
more » ... .8 to -2.4 and depends on the downstream turbulence level. For sufficiently strong turbulence, we find α_ e≃ -2.2, and both the photon index and the flux of 1-100 keV X-rays from the Crab Nebula, as measured by NuSTAR, can be reproduced. The particle spectrum hardens to α_ e≃ -1.8 at lower turbulence levels, which may explain the hard photon index observed by the Chandra X-ray Observatory in the central regions of the Nebula.
doi:10.3847/1538-4357/aacffb fatcat:jcclohtbqvg5tclxn6ubjrkqvy