The origin of the high energy gamma-ray emission from the Crab nebula - clues from the spatial extension and energy spectrum

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The Crab nebula is the remnant of a historical supernova from the year 1054. The nebula has been observed in great detail at every accessible energy from radio frequency to gamma-rays at 100 TeV. Most of the observed radiation is synchrotron emission of energetic particles originating in the steady pulsar wind emitted by the Crab pulsar. The energetic particles are deflected by the magnetic field (of largely unknown structure and strength) permeating the nebula. With recent observations of the nebula with Fermi-LAT we have been able to demonstrate that the nebula can be spatially resolved at energies above a few GeV. In this project, we will analyse both the data taken with Fermi-LAT as well as with the H.E.S.S. telescopes in order to determine the energy dependent size of the gamma-nebula. Jointly with the observed integrated spectrum, we will be able to spatially characterize the underlying electron energy distribution. The required assumption is an inverse Compton origin of the gamma-radiation,i.e., energetic electrons up-scatter lower energy photon fields present in the nebula. Given the detailed observations, we will refine the available radiation field estimates to include the emission from the dusty plasma at the boundary of the synchrotron nebula. Finally, we will estimate the magnetic field and its large-scale structure present in the nebula using our estimate of the spatial and spectral distribution of particles. In order to exclude that the results are influenced by additional radiative components at gamma-rays, we will study as an alternative non-thermal Bremsstrahlung emitted from the dense regions of the nebula. The result of the study will be an in-depth understanding of the energy dependent spatial distribution of electrons in the nebula and consequently will be prepared to answer the question on the origin of the gamma-ray emission of the Crab nebula.