Properties of individual X-ray sources: (Invited discourse)

Abstract

Observations to determine the spectra and time variations of hard X-rays from cosmic sources have been made from balloons and from the OSO-III satellite. These data have been obtained using actively collimated scintillation counters with apertures between 6 and 24° FWHM, areas between 10 and 50 cm2 and which operate over the 10–300 keV range. The Crab Nebula has been observed on three occasions over a 22-month period between September 1965 and July 1967. The power law spectrum has a number index of 2.0 ± 0.1. No long-term changes were observed over the 30–100 keV range with a limit at 3%/yr. A balloon search with a 10 cm2 Ge(Li) detector for X-ray lines at 62.5 keV, 110 keV and 180 keV due to heavy element radioactive decays which would be produced in the initial Crab explosion based on the Cf254 hypothesis has resulted in upper limits at about 10−3 γ-rays cm2-sec. This is about a factor of 20 above the predicted levels. Simultaneous X-ray and optical observations of SCO XR-1 from OSO-III confirm that X-ray and optical flaring are indeed coincident phenomena, and that although the X-ray intensity increases about a factor of two during the flare, the equivalent temperature of the excess radiation is nearly the same as that of the quiescent object. Upper limits, 95% confidence, on the flux of M-87 at 40 keV have been obtained. These are inconsistent with the flux of 1.2 × 10−4 photons/cm2-sec-keV reported in the literature. CYG X-1 has been observed to have a power law of number index 2.0 ± 0.2. The OSO-III has observed a number of sources in the southern skies including NOR XR-2 and the variable source Centaurus XR-2.