Mon. Not. R. Astron. Soc., 439, 3931-3950 (2014/April-3)
General relativistic modelling of the negative reverberation X-ray time delays in AGN.
EMMANOULOPOULOS D., PAPADAKIS I.E., DOVCIAK M. and McHARDY I.M.
Abstract (from CDS):
We present the first systematic physical modelling of the time-lag spectra between the soft (0.3-1keV) and the hard (1.5-4keV) X-ray energy bands, as a function of Fourier frequency, in a sample of 12 active galactic nuclei which have been observed by XMM-Newton. We concentrate particularly on the negative X-ray time-lags (typically seen above 10–4Hz), i.e. soft-band variations lag the hard-band variations, and we assume that they are produced by reprocessing and reflection by the accretion disc within a lamp-post X-ray source geometry. We also assume that the response of the accretion disc, in the soft X-ray bands, is adequately described by the response in the neutral Fe Kα line at 6.4keV for which we use fully general relativistic ray-tracing simulations to determine its time evolution. These response functions, and thus the corresponding time-lag spectra, yield much more realistic results than the commonly used, but erroneous, top-hat models. Additionally, we parametrize the positive part of the time-lag spectra (typically seen below 10–4Hz) by a power law. We find that the best-fitting black hole (BH) masses, M, agree quite well with those derived by other methods, thus providing us with a new tool for BH mass determination. We find no evidence for any correlation between M and the BH spin parameter, α, the viewing angle, θ, or the height of the X-ray source above the disc, h. Also on average, the X-ray source lies only around 3.7 gravitational radii above the accretion disc and θ is distributed uniformly between 20° and 60°. Finally, there is a tentative indication that the distribution of α may be bimodal above and below 0.62.
© 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society (2014)
accretion, accretion discs - black hole physics - relativistic processes - galaxies: active - galaxies: nuclei - X-rays: galaxies
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