Particle acceleration model for the broadband baseline spectrum of the Crab nebula [HEAP]

We develop a simple one-zone model of the steady-state Crab nebula spectrum encompassing both the radio/soft $X$-ray and the GeV/multi-TeV observations. We determine analytically the photon differential energy spectrum as originated by an electron distribution evolved from a log-parabola injection spectrum: we find an impressive agreement with the synchrotron region observations whereas synchrotron self-Compton accommodates the previously unsolved origin of the broad $200$ GeV peak that matches the Fermi/LAT data beyond $1$ GeV with the MAGIC data. We determine the parameters of the log-parabola electron distribution, ruling out a simple power-law. The scale of the acceleration region is found to be $ \sim 3.8 \times 10^{-4}$ pc. The resulting photon differential spectrum provides a natural interpretation of the deviation from power-law customarily fit with empirical broken power-laws. Our model can be applied to the radio-to-multi-TeV spectrum of a variety of astrophysical sources of relativistic flows as well as to fast interplanetary shocks.

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F. Fraschetti and M. Pohl
Mon, 6 Feb 17

Comments: 8 pages, 7 figures. Submitted. Comments welcome