Timing studies of Seyfert galaxies with the Rossi X-ray timing explorer
Timing studies of Seyfert galaxies with the Rossi X-ray timing explorer
Previous studies of the X-ray variability power spectra of active galactic nuclei (AGN) on time-scales of hours to days revealed striking similarities to the timing properties of black hole X-ray binary systems (XRBs) on much shorter time-scales (< 1 s). The unique capabilities of the Rossi X-ray Timing Explorer (RXTE) mission allow us to sample AGN lightcurves over a far greater range of time-scales than before, enabling us to compare the broadband power spectrum of AGN with that of XRBs. Here we present the results of an RXTE program to monitor 4 Seyfert galaxies (NGC 4051, MCG-6-30-15, NGC 5506 and NGC 5548) to measure their power spectra from 10-8 Hz to 10-2 Hz.
We use RXTE long-look observations to show that the power spectra of our sample are intrinsically non-stationary, in that their RMS variability scales with local mean flux. We show that this relation also applies to the black hole XRB Cygnus X-1 and the accreting millisecond pulsar SAX J1808.4-3658 and is highly linear, implying that it is intrinsic to the red-noise variability process which dominates the X-ray lightcurves of accreting compact objects. The scaling of RMS variability with flux occurs on all measured time-scales, posing problems for models where lightcurves are made from small building blocks, such as conventional shot-noise models. We suggest that the lightcurves are built from the top down, out of large flaring events which break up into self-similar structure on smaller scales.
Discrete sampling of lightcurves causes distortion in the observed power spectrum due to red-noise leak and aliaising effects. We develop a Monte Carlo technique, based on the 'response method' of Done et al. (1992), to robustly estimate the shape of the underlying broadband power spectrum. We apply this technique to our data, and data obtained from a separate program to monitor the Seyfert galaxy NGC 3516. We find that the broad-band power spectra of MCG-6-30-15, NGC 5506 and NGC 3516 flatten significantly at low frequencies, and that this flattening can be well fitted by a high-frequency break mode analogous to the shape of the high-frequency power spectrum of Cygnus X-1.
University of Southampton
Uttley, Philip
9a24b878-479e-4e22-a981-a421e82df2fa
2000
Uttley, Philip
9a24b878-479e-4e22-a981-a421e82df2fa
Uttley, Philip
(2000)
Timing studies of Seyfert galaxies with the Rossi X-ray timing explorer.
University of Southampton, Doctoral Thesis.
Record type:
Thesis
(Doctoral)
Abstract
Previous studies of the X-ray variability power spectra of active galactic nuclei (AGN) on time-scales of hours to days revealed striking similarities to the timing properties of black hole X-ray binary systems (XRBs) on much shorter time-scales (< 1 s). The unique capabilities of the Rossi X-ray Timing Explorer (RXTE) mission allow us to sample AGN lightcurves over a far greater range of time-scales than before, enabling us to compare the broadband power spectrum of AGN with that of XRBs. Here we present the results of an RXTE program to monitor 4 Seyfert galaxies (NGC 4051, MCG-6-30-15, NGC 5506 and NGC 5548) to measure their power spectra from 10-8 Hz to 10-2 Hz.
We use RXTE long-look observations to show that the power spectra of our sample are intrinsically non-stationary, in that their RMS variability scales with local mean flux. We show that this relation also applies to the black hole XRB Cygnus X-1 and the accreting millisecond pulsar SAX J1808.4-3658 and is highly linear, implying that it is intrinsic to the red-noise variability process which dominates the X-ray lightcurves of accreting compact objects. The scaling of RMS variability with flux occurs on all measured time-scales, posing problems for models where lightcurves are made from small building blocks, such as conventional shot-noise models. We suggest that the lightcurves are built from the top down, out of large flaring events which break up into self-similar structure on smaller scales.
Discrete sampling of lightcurves causes distortion in the observed power spectrum due to red-noise leak and aliaising effects. We develop a Monte Carlo technique, based on the 'response method' of Done et al. (1992), to robustly estimate the shape of the underlying broadband power spectrum. We apply this technique to our data, and data obtained from a separate program to monitor the Seyfert galaxy NGC 3516. We find that the broad-band power spectra of MCG-6-30-15, NGC 5506 and NGC 3516 flatten significantly at low frequencies, and that this flattening can be well fitted by a high-frequency break mode analogous to the shape of the high-frequency power spectrum of Cygnus X-1.
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Published date: 2000
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Local EPrints ID: 467027
URI: http://eprints.soton.ac.uk/id/eprint/467027
PURE UUID: e9c605d3-af5a-4f26-8a95-f12f5bd4ed24
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Date deposited: 05 Jul 2022 08:09
Last modified: 16 Mar 2024 20:56
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Author:
Philip Uttley
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