A measurement of hard X and gamma radiation from Sco X-1

Sco X-1 is the brightest extrasolar X-ray source in the sky. Additional knowledge of its output in the hard X-ray and gamma-ray regions could be particularly valuable in judging the validity of hypotheses intended to explain its unusual emission characteristics. On November 26, 1969, a balloon-borne scintillation detector was launched from Parana, Argentina to measure the output of Sco X-1 above 110 keV. Despite complications caused by a partial battery failure and a solar X-ray flare, a flux above 75 keV was measured. The instrument and experimental procedures are discussed briefly, and the reduction procedures and calculated fluxes are presented and discussed. Because of a possible solar contribution, the measured fluxes are interpreted as upper limits, but the results appear to verify the existence of a previously observed possibly non-thermal flux component departing at about /10 keV from the softer thermal component. Observations of Sco X-1 in the X-ray, visual, infrared, and microwave regions are reviewed. Derived source parameters and proposed models for the source are discussed in an appendix. No hypothesis has thus far been completely successful in explaining the many unusual characteristics of the electromagnetic emission of Sco X-1, but the close-binary hypothesis may be the most satisfactory