Modelling X-ray RMS spectra II: the ultra-fast outflow of PDS 456

Abstract

We present an improved model for excess variance spectra describing ultra-fast outflows and successfully apply it to the luminous (L ~ 10^47 erg/s) low-redshift (z = 0.184) quasar PDS 456. The model is able to account well for the broadening of the spike-like features of these outflows in the excess variance spectrum of PDS 456, by considering two effects: a correlation between the outflow velocity and the logarithmic X-ray flux and intrinsic Doppler broadening with v_int = 10^4 km/s. The models were generated by calculating the fractional excess variance of count spectra from a Monte Carlo simulation. We find evidence that the outflow in PDS 456 is structured, i.e., that there exist two or more layers with outflow velocities 0.27-0.30 c, 0.41-0.49 c, and 0.15-0.20 c for a possible third layer, which agrees well with the literature. We discuss the prospects of generally applicable models for excess variance spectra for detecting ultra-fast outflows and investigating their structure. We provide an estimate for the strength of the correlation between the outflow velocity and the logarithmic X-ray flux and investigate its validity.

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Cited by in corpus (6)

• The nature of the extreme X-ray variability in the NLS1 1H 0707-495
• The X-ray Disk/Wind Degeneracy in AGN
• Magnetohydrodynamic Winds Driven by the Line Force from the Standard Thin Disk around Supermassive Black Holes. I. The Case of Weak Magnetic Field
• Stellar wind variability in Cygnus X-1 from high-resolution excess variance spectroscopy with Chandra
• A Systematic Study of the Short-Term X-ray Variability of Seyfert Galaxies I. Diversity of the X-ray Rms Spectra
• Effects of ultra-fast outflows on X-ray time lags in AGN