The X-ray variability of AGN: power-spectrum and variance analysis of the Swift/BAT light curves
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2024
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| author | Papadakis, I. E. Binas-Valavanis, V. |
| author_facet | Papadakis, I. E. Binas-Valavanis, V. |
| contents | We study the X-ray power spectrum of Active Galactic Nuclei (AGN) to investigate whether Seyfert I and II power spectra are similar or not, whether the AGN variability depends on black hole mass and accretion rate, and to compare the AGN power spectra with the Galactic X-ray black hole binaries power-spectra. We used 14-195 keV band light curves from the 157th SWIFT/BAT hard X-ray survey and we computed the mean power spectrum and excess variance of AGN in narrow black-hole mass/luminosity bins. We fitted a power-law model to the AGN power spectra, and we investigated whether the power spectrum parameters and the excess variance depend on black hole mass, luminosity and accretion rate. The Seyfert I and Seyfert II power spectra are identical, in agreement with AGN unification models. The mean AGN X-ray power spectrum has the same, power-law like shape with a slope of -1 in all AGN, irrespective of their luminosity and BH mass. We do not detect any flattening to a slope of zero at frequencies as low as 10e-9 Hz. We detect an anti-correlation between the PSD amplitude and the accretion rate, similar to what has been seen in the past in the 2-10 keV band. This implies that the variability amplitude in AGN decreases with increasing accretion rate. The universal AGN power-spectrum is consistent with the mean, 2-9 keV band Cyg X-1 power spectrum in its soft state. The mean, low frequency AGN X-ray power spectrum is consistent with the extension of the mean, 0.01-25 Hz Cyg X-1 power spectrum to lower frequencies. The agreement between the AGN and the Cyg X-1 power spectrum (either in the soft or the hard state) over many decades in frequency indicates that the X-ray variability process is probably the same in all accreting objects, irrespective of the mass of the compact object. We plan to investigate this issue further in the near future. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2402_15373 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | The X-ray variability of AGN: power-spectrum and variance analysis of the Swift/BAT light curves Papadakis, I. E. Binas-Valavanis, V. Astrophysics of Galaxies High Energy Astrophysical Phenomena We study the X-ray power spectrum of Active Galactic Nuclei (AGN) to investigate whether Seyfert I and II power spectra are similar or not, whether the AGN variability depends on black hole mass and accretion rate, and to compare the AGN power spectra with the Galactic X-ray black hole binaries power-spectra. We used 14-195 keV band light curves from the 157th SWIFT/BAT hard X-ray survey and we computed the mean power spectrum and excess variance of AGN in narrow black-hole mass/luminosity bins. We fitted a power-law model to the AGN power spectra, and we investigated whether the power spectrum parameters and the excess variance depend on black hole mass, luminosity and accretion rate. The Seyfert I and Seyfert II power spectra are identical, in agreement with AGN unification models. The mean AGN X-ray power spectrum has the same, power-law like shape with a slope of -1 in all AGN, irrespective of their luminosity and BH mass. We do not detect any flattening to a slope of zero at frequencies as low as 10e-9 Hz. We detect an anti-correlation between the PSD amplitude and the accretion rate, similar to what has been seen in the past in the 2-10 keV band. This implies that the variability amplitude in AGN decreases with increasing accretion rate. The universal AGN power-spectrum is consistent with the mean, 2-9 keV band Cyg X-1 power spectrum in its soft state. The mean, low frequency AGN X-ray power spectrum is consistent with the extension of the mean, 0.01-25 Hz Cyg X-1 power spectrum to lower frequencies. The agreement between the AGN and the Cyg X-1 power spectrum (either in the soft or the hard state) over many decades in frequency indicates that the X-ray variability process is probably the same in all accreting objects, irrespective of the mass of the compact object. We plan to investigate this issue further in the near future. |
| title | The X-ray variability of AGN: power-spectrum and variance analysis of the Swift/BAT light curves |
| topic | Astrophysics of Galaxies High Energy Astrophysical Phenomena |
| url | https://arxiv.org/abs/2402.15373 |