Time variation of the optical intensity of the Sco X-1 X-ray source

Abstract

Since the optical identification of Sco X-1 by Sandage et al., a large number of photometric observations of Sco X-1 have been made by Mook and by Hiltner and Mook. The UBV colour photometric observations of Hiltner and Mook and of Stepien reveal that the V and B magnitudes of Sco X-1 vary between 12.2 and 13.2 and that, during roughly half of the time when it is brighter than magnitude 12.6, it shows considerable flickering activity. Attempts by Hiltner and Mook to find short time periodicities in the flickers have not been very successful. The importance of looking for hidden long term periodicities and for correlated changes in the X-ray emission has been pointed out by Oda. The recent observation by Lewin et al. of an X-ray flare from Sco X-1 of magnitude 1.5 lasting 20 min further confirms the view that the variations at different wavelengths may have a common origin.