An atlas of aperiodic variability in HMXB.

Abstract

From EXOSAT archive data of 14 X-ray binaries (12 high mass X-ray binaries and 2 low mass X-ray binaries) broad band power spectra and color- color diagrams are produced. The aperiodic (noise) variability of the sources is studied. All the X-ray pulsars present in the sample show strong noise components in the emission, with a fractional variability between 20 and 30%. The shape of these noise components is quite complex and cannot be fitted to a simple analytical law as in the case of low mass sources. The black hole candidate Cyg X-1 is the only non-pulsing source in the sample showing a high rms (35%) noise. The shape of the power spectrum of Cyg X-1 appears to be more complex than a simple shot noise model. Some of the sources are also observed in a low noise state (rms ~ 10-15%). The correlations between these variations and other characteristics of the sources are analyzed. The possible connections between these properties and those observed in LMXB are discussed.