Low frequency quasi-periodic oscillations in the hard X-ray emission from Cygnus X-1

Abstract

The observations of the black hole binary Cygnus X-1 were made in the energy band of 20 - 100 keV with a balloon-borne Xenon-filled multiwire proportional counter telescope on 5th April 1992. Timing analysis of the data revealed the presence of quasi-periodic oscillations (QPO) in the hard X-ray emission from the source. The QPO feature in the power density spectrum is broad with a peak at a frequency of 0.06 Hz. This result is compared with similar reports of QPOs in Cyg X-1 in soft and hard X-rays. Short time scale random intensity variations in the X-ray light curve are described with a shot noiuse model.