IUE observations of Centaurus X-4 during the 1979 May outburst.

Ultraviolet spectrophotometry of the X-ray transient/burst source Centaurus X-4 at several intervals during the peak and decay of the May 1979 X-ray transient event was obtained. The spectrum was characterized by a blue continuum with alpha = 0.0 + or - 0.3 (F/nu/ varies as nu to the alpha power) and strong emission lines of N V lambda 1240, C IV lambda 1550, and Si IV lambda 1398. The relative intensities of the emission lines and the ratio of line to continuum strengths remained nearly constant during the decline. The emission lines may have arisen from a 'disk chromosphere', from X-ray heating of the K4 V companion star, or both. The ultraviolet data are combined with previously published optical and X-ray data to determine some of the physical characteristics of the system and to show that X-ray reprocessing plays an important role in producing the optical and ultraviolet continua.