THE EXPECTED HIGH-ENERGY TO ULTRA HIGH-ENERGY GAMMA-RAY SPECTRUM OF THE CRAB-NEBULA

In this paper we reexamine the inverse Compton scattering model for the unpulsed TeV emission from the Crab Nebula, using the magnetic field distribution derived from MHD flow models of the nebula. We show that the observed flux can be explained if the average nebular field is indeed almost-equal-to 3 x 10(-4) G as is predicted by the spectral break between radio and optical. The calculated spectral index at TeV energies also agrees with the observed value. The only free parameter in the TeV gamma-ray flux estimate is sigma, i.e., the ratio between the electromagnetic and particle pressures at the pulsar wind shock. From the TeV data we find sigma less-than-or-equal-to 0.003, which is also consistent with previous estimates from MHD flow models which suggested that sigma almost-equal-to 0.001-0.003. The brightness distribution of the TeV gamma-ray signal is expected to extend out to almost-equal-to 1'5 from the pulsar which may be resolved with the next generation of imaging air Cherenkov telescopes. The flux of unpulsed high-energy gamma-rays seen by COS B is too high to be explained by this inverse Compton component but could be explained by synchrotron radiation requiring electrons with energies up to at least 10(16) eV, possibly accelerated at the shock in the pulsar wind. Our estimates also predict a steady flux of unpulsed ultra-high-energy gamma-rays due to the inverse Compton scattering of soft photons by such shock-accelerated electrons and/or positrons in the vicinity of the shock which should be detectable with sensitive extensive air shower detectors if sigma < 0.003. The observable gamma-ray spectrum between a few hundred MeV and almost-equal-to 1 PeV can provide us with a good estimate of the magnetic field distribution and the maximum acceleration energy in the nebula.