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Power colours: simple X-ray binary variability comparison
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DOI：10.1093/mnras/stv191.png)
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Abstract
En 中文
We demonstrate a new method of variability classification using observations of black hole Xray binaries. Using 'power colours' - ratios of integrated power in different Fourier frequency bands - we can clearly differentiate different canonical black hole states as the objects evolve during outburst. We analyse (similar to 2400) Rossi X-ray Timing Explorer observations of 12 transient low-mass black hole X-ray binaries and find that the path taken around the power colour-colour diagram as the sources evolve is highly consistent from object to object. We discuss how the consistency observed in the power colour-colour diagram between different objects allows for easy state classification based on only a few observations, and show how the power-spectral shapes can be simply classified using a single parameter, the power-spectral 'hue'. To illustrate the benefits of our simple model-independent approach, we show that the persistent high-mass X-ray binary Cyg X-1 shows very similar power-spectral evolution to the transient black hole sources, with the main difference being caused by a combination of a lack of quasi-periodic oscillations and an excess of low-frequency power-law noise in the Cyg X-1 power spectra during the transitional state. We also compare the transient objects to the neutron star atoll source Aquila X-1, demonstrating that it traces a different path in the power colour-colour plot. Thus, power colours could be an effective method to classify newly discovered X-ray binaries.
Keywords:
X-rays: binaries
X-rays: general
X-rays: individual: Cygnus X-1
X-rays: individual: Aquila X-1
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