observational overview of state transitions in x-ray binaries

RAPID X-RAY VARIABILITY
• power density spectra (1 mHz - 1 kHz)
• broad (noise) and narrow (QPO) components
• correlates with spectral properties and map well
onto HID
When I talk about rapid variability, I typically mean frequencies between 1 mHz and 1 kHz.
This rapid variability is often studied terms in terms of power spectra, since most of the
variability is too fast and/or too weak to be seen directly in the light curve. As Phil Uttley
showed this morning, the power spectra often show combinations of broad components,
which are often referred to as noise, and narrow features referred to as quasi-periodic
oscillations, or QPOs. The rapid X-ray variability changes strongly between states and their
evolution maps well onto the HID.