Discovery of 0.08-Hz quasi-periodic oscillations from the black-hole candidate LMC X-1.

In the X-ray flux of LMC X-1, quasi-periodic oscillatiosn (QPO) of centroid frequency 0.0751 + or - 0.0009 Hz were discovered. Observations were made on April 22 and on July 16, 1987 with the large area proportional counters (LAC) on Ginga. QPOs were detected only in the April data. The energy spectrum of LMC X-1 is well represented by a two-component model consisting of an ultrasoft component with a color temperature of 0.7 keV and a hard-tail component which can be represented by a power-law function with a photon index of 2.0. The spectrum in July was softer than the spectrum in April, which is attributed to the decrease of the hard-tail component in the July observation.