ON THE CRAB-NEBULA VHE GAMMA-RAY FLUX

The VHE gamma-ray flux of the Crab Nebula has been observed for many t imes by different groups in various energy ranges. The comparison of t hese data shows that values of fluxes obtained by various groups and v arious methods are not in agreement. It seems to us that this disagree ment is mostly connected with differences in concepts of the effective area and in the energy threshold evaluation used by different groups. We propose a method of a flux derivation which do not use these conce pts and permits us to obtain the correct value of the flux. Applied to data obtained in the Crimean Astrophysical Observatory, (1.3 +/- 0.4) . 10(-11) quanta cm(-2)s(-1) is obtained for the flux above 1 TeV. The Crab Nebula VHE gamma-ray flux was derived on the basis of theoretica l models. The calculation of De Jager and Harding agrees with the obse rvations in the case of a relatively low magnetic field strength. The calculation derived by the present author gives, in contrast, a low ga mma-ray flux. It is concluded that further investigations of the Crab Nebula are to be carried out.