Hard X-ray measurements of nova A0535+26 in Taurus

Measurements are described of high energy x-rays in the region of the Crab Nebula by the satellite Ariel V between April 13th and April 29th 1975. During this period the x-ray nova A0535 + 26 was first detected and observed to reach its maximum intensity, the intensity rising to a value considerably brighter than the Crab at 30 keV, making it the brightest known source in the sky. The detection apparatus employed a shielded crystal scintillator, operating in the range 26 keV to 1.2 Mev. The spectra showed some evidence of steepening as the nova brightened. Information on the spectral development is shown graphically. The results can be interpreted in terms of accretion of material from a normal star on to a compact object like a neutron star, and point to a multilayer multitemperature source model, and the relatively constant shape of the spectrum during flare-up of the source is consistent with an accretion model in a binary system. (U.K.)