Low and medium energy gamma radiation from the Crab Nebula

Abstract

The Crab Nebula was observed for 58 minutes in the .6 to 12 MeV energy range in the first successful flight of Gammascope VI. A continuum of radiation in the .6 to .6 MeV energy range was detected. Upper limits for the 1 to 12 MeV energy range were established. The sensitivity of the detector was established for the range of .6 to 12 MeV by comparison with other experiments. The data for this energy range is more detailed than that of previous experiments covering portions of this energy range. The emission of the Earth's atmosphere in the 1-12 MeV range combined with leakage of radiation in this range by the detector produced poor statistics in the 1 to 1-12 MeV energy range. A possible spectral feature is noticed in the 1 keV energy range. This possible feature is a weak peak of no more than one standard deviation above a curve fit of the data but is consistent with the "bump" at that energy in the spectrum of Peterson etal. (1968). The synchotron mechanism Is supported by the experiment's low energy data. A map of the source of background Is presented indicating that three minor sources of X-rays were 1n or near the field of view during background measurements. It is not thought that these faint sources caused significant contamination of the Crab data. The higher energy data could be accounted for by a source of MeV photons that could correspond to one of these three sources. Such a source is thought highly unlikely because it would imply that the source emitts predominantly from nuclear reactions and thus would be different from any previously known astrophysical objects. However, the most likely explanation of the poor statistics in evidence in the 1-12 MeV energy range is seen to be leakage of the detector to such high energy photons combined with the dominance of the Earth's atmosphere as an emitter of 1-12 MeV energy photons over celestial sources. The 1-12 MeV data is better fit by an extrapolation of lower energy data rather than the decreased spectral index appropriate to Baker et. al. (1973). A power law of the form [equation] was found to best fit the data of this experiment.