Engineering topics
Publications and source records attributed to Brainerd, J..
New observational and theoretical results strongly suggest that QPOs in the fast, luminous sources are caused by oscillations in the luminosity of the X-ray star. They also explain why coherent pulsations at the stellar rotation frequency are so weak in these sources. Observations of weak red noise suggest that the luminosity oscillations in some sources are partially coherent.
The effect of a scattering cloud on the amplitude of oscillations produced by a rotating beam of X-rays is investigated using analytical and Monte Carlo methods. The scattering cloud was modeled as a uniform density sphere, and the source was represented as an anistropic distribution of radiation emerging from a point at the center of the scattering cloud. The intensity distribution produced by the source beam is examined as a function of optical depth. The relation between electron scattering optical depth and the forward-backward ratio is studied. It is observed that the scattering in a central corona of various optical depths reduces the amplitude of the oscillation. The data suggest that the quasi-periodic oscillations observed in the X-ray intensities of some luminous low-mass X-ray binaries are caused by oscillations in the luminosity of the X-ray star.