On the production of power-law spectra and the evolution of cosmic synchrotron sources - A model for the Crab Nebula

Details On the production of power-law spectra and the evolution of cosmic synchrotron sources - A model for the Crab Nebula On the production of power-law spectra and the evolution of cosmic synchrotron sources - A model for the Crab Nebula

Dec 1975

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1975apj...202..773c&link_type=abstract

Astrophysical Journal, vol. 202, Dec. 15, 1975, pt. 1, p. 773-781.

Astronomy and Astrophysics

Astrophysics

20

Cosmic Rays, Crab Nebula, Radio Spectra, Synchrotron Radiation, X Ray Spectra, Astronomical Models, Diffusion Theory, Pulsar Magnetospheres, Pulsars, Relativistic Particles, Stellar Spectra

Scientific paper

Certain solutions of the energy-diffusion equation for ultrarelativistic electrons undergoing Fermi acceleration are investigated. Two special cases are considered which produce power-law electron spectra in a natural way and are applicable to models of expanding synchrotron sources. These are applied to the Crab Nebula, where Fermi acceleration seems necessary to provide electrons energetic enough to produce the observed nebular X-rays. Curvature radiation losses prevent their being produced in the pulsar magnetosphere. The model gives a satisfactory fit to the overall nebular spectrum and avoids certain difficulties associated with the conventional model, the most important difficulty being that the difference between the radio and X-ray spectral indices is observed to be 1.0 whereas the conventional model predicts 0.5. The results indicate magnetic fields of 0.0002 gauss in the outer reaches of the nebula and 0.00003 gauss near the pulsar, where Fermi acceleration is believed to occur and where hydromagnetic activity is observed. A cutoff in the nebular gamma-ray spectrum between 1 and 10 MeV is predicted.

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