Balloon observations of the 5-100 MeV gamma rays from the Crab Nebula

Gamma-ray observations of the Crab Nebula, obtained with the Natalya-1 balloon-borne gamma-ray telescope over India on Nov. 6-7, 1980, are reported. The instrument comprises 18 wire spark chambers separated by lead converter layers and divided into three sections, anticoincidence scintillation counters, a directional Cerenkov counter, and standard photomultiplier tubes, and covers the range from 5 to 100 MeV; the data-analysis procedures are described in detail. A total of 3700 events are analyzed, and the differential intensities at 5-20 and 20-100 MeV are found to be (21 + or - 3) x 10 to the -6th photon/sq cm s MeV and (1.0 + 0.1 or - 0.2) x 10 to the -6th photon/sq cm s MeV, respectively, corresponding to a spectral index of -2.2.