Upper limits on pulsations from Cyg X-1 in hard X-rays

Abstract

In an earlier communication1 we presented evidence for short term variations in the intensity of Cyg X-1 in the energy band 22.5-154 keV based on observations with a balloon-borne oriented X-ray telescope that monitored the intensity of this source between 0002 and 0315 UT on April 6, 1971. In the light of the findings of Oda et al. 2 and Holt et al. 3 about the possible presence of pulsating components in the X-ray emission of Cyg X-1 at energies of a few keV, we have analysed the data of April 6 to see whether similar pulsations are also present in the higher energy band. The instrumental details, the flight performance, the methods of recording, classification and analysis of data to obtain the contribution of Cyg X-1 to the counting rate of the telescope during the 3 h exposure are given in ref. 1.