High-frequency X-ray variability as a mass estimator of stellar and supermassive black holes |
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Authors: | Marek Gierliski Marek Nikoajuk Boena Czerny |
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Institution: | Department of Physics, University of Durham, South Road, Durham DH1 3LE;Astronomical Observatory, Jagiellonian University, Orla 171, 30-244 Kraków, Poland;Department of Physics, University of Bia?ystok, Lipowa 41, 15-424 Bia?ystok, Poland;Copernicus Astronomical Centre, Bartycka 18, 00-716 Warszawa, Poland |
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Abstract: | There is increasing evidence that supermassive black holes in active galactic nuclei (AGN) are scaled-up versions of Galactic black holes. We show that the amplitude of high-frequency X-ray variability in the hard spectral state is inversely proportional to the black hole mass over eight orders of magnitude. We have analysed all available hard-state data from RXTE of seven Galactic black holes. Their power density spectra change dramatically from observation to observation, except for the high-frequency (?10 Hz) tail, which seems to have a universal shape, roughly represented by a power law of index ?2. The amplitude of the tail, C M (extrapolated to 1 Hz), remains approximately constant for a given source, regardless of the luminosity, unlike the break or quasi-periodic oscillation frequencies, which are usually strongly correlated with luminosity. Comparison with a moderate-luminosity sample of AGN shows that the amplitude of the tail is a simple function of black hole mass, C M = C / M , where C ≈ 1.25 M⊙ Hz?1 . This makes C M a robust estimator of the black hole mass which is easy to apply to low- to moderate-luminosity supermassive black holes. The high-frequency tail with its universal shape is an invariant feature of a black hole and, possibly, an imprint of the last stable orbit. |
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Keywords: | accretion accretion discs galaxies: active X-rays: binaries |
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