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The remarkable X-ray variability of IRAS 13224–3809 – I. The variability process

The remarkable X-ray variability of IRAS 13224–3809 – I. The variability process
The remarkable X-ray variability of IRAS 13224–3809 – I. The variability process
We present a detailed X-ray timing analysis of the highly variable narrow-line Seyfert 1 (NLS1) galaxy IRAS 13224–3809. The source was recently monitored for 1.5 Ms with XMM–Newton, which, combined with 500 ks archival data, makes this the best-studied NLS1 galaxy in X-rays to date. We apply standard time- and Fourier-domain techniques in order to understand the underlying variability process. The source flux is not distributed lognormally, as expected for all types of accreting sources. The first non-linear rms–flux relation for any accreting source in any waveband is found, with rms ∝ flux2/3. The light curves exhibit significant strong non-stationarity, in addition to that caused by the rms–flux relation, and are fractionally more variable at lower source flux. The power spectrum is estimated down to ∼10−7 Hz and consists of multiple peaked components: a low-frequency break at ∼10−5 Hz, with slope α < 1 down to low frequencies, and an additional component breaking at ∼10−3 Hz. Using the high-frequency break, we estimate the black hole mass MBH=[0.5−−2]×106M⊙ and mass accretion rate in Eddington units, m˙Edd≳1⁠. The broad-band power spectral density (PSD) and accretion rate make IRAS 13224–3809 a likely analogue of very high/intermediate-state black hole X-ray binaries. The non-stationarity is manifest in the PSD with the normalization of the peaked components increasing with decreasing source flux, as well as the low-frequency peak moving to higher frequencies. We also detect a narrow coherent feature in the soft-band PSD at 7 × 10−4 Hz; modelled with a Lorentzian the feature has Q ∼ 8 and an rms ∼3 per cent. We discuss the implication of these results for accretion of matter on to black holes.
0035-8711
2088-2106
Alston, W.N.
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Fabian, A.C.
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Buisson, D.J.K.
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Kara, E.
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Parker, M.L.
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Lohfink, A.M.
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Uttley, P.
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Wilkins, D.R.
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Pinto, C.
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De Marco, B.
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Cackett, E.M.
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Middleton, M.J.
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Walton, D.J.
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Reynolds, C.S.
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Jiang, J.
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Gallo, L.C.
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Zogbhi, A.
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Miniutti, G.
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Dovciak, M.
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Young, A.J.
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Alston, W.N.
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Fabian, A.C.
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Buisson, D.J.K.
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Kara, E.
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Parker, M.L.
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Lohfink, A.M.
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Uttley, P.
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Wilkins, D.R.
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Pinto, C.
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De Marco, B.
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Cackett, E.M.
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Middleton, M.J.
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Walton, D.J.
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Reynolds, C.S.
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Jiang, J.
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Gallo, L.C.
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Zogbhi, A.
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Miniutti, G.
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Dovciak, M.
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Young, A.J.
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Alston, W.N., Fabian, A.C., Buisson, D.J.K., Kara, E., Parker, M.L., Lohfink, A.M., Uttley, P., Wilkins, D.R., Pinto, C., De Marco, B., Cackett, E.M., Middleton, M.J., Walton, D.J., Reynolds, C.S., Jiang, J., Gallo, L.C., Zogbhi, A., Miniutti, G., Dovciak, M. and Young, A.J. (2019) The remarkable X-ray variability of IRAS 13224–3809 – I. The variability process. Monthly Notices of the Royal Astronomical Society, 482 (2), 2088-2106. (doi:10.1093/mnras/sty2527).

Record type: Article

Abstract

We present a detailed X-ray timing analysis of the highly variable narrow-line Seyfert 1 (NLS1) galaxy IRAS 13224–3809. The source was recently monitored for 1.5 Ms with XMM–Newton, which, combined with 500 ks archival data, makes this the best-studied NLS1 galaxy in X-rays to date. We apply standard time- and Fourier-domain techniques in order to understand the underlying variability process. The source flux is not distributed lognormally, as expected for all types of accreting sources. The first non-linear rms–flux relation for any accreting source in any waveband is found, with rms ∝ flux2/3. The light curves exhibit significant strong non-stationarity, in addition to that caused by the rms–flux relation, and are fractionally more variable at lower source flux. The power spectrum is estimated down to ∼10−7 Hz and consists of multiple peaked components: a low-frequency break at ∼10−5 Hz, with slope α < 1 down to low frequencies, and an additional component breaking at ∼10−3 Hz. Using the high-frequency break, we estimate the black hole mass MBH=[0.5−−2]×106M⊙ and mass accretion rate in Eddington units, m˙Edd≳1⁠. The broad-band power spectral density (PSD) and accretion rate make IRAS 13224–3809 a likely analogue of very high/intermediate-state black hole X-ray binaries. The non-stationarity is manifest in the PSD with the normalization of the peaked components increasing with decreasing source flux, as well as the low-frequency peak moving to higher frequencies. We also detect a narrow coherent feature in the soft-band PSD at 7 × 10−4 Hz; modelled with a Lorentzian the feature has Q ∼ 8 and an rms ∼3 per cent. We discuss the implication of these results for accretion of matter on to black holes.

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The remarkable X-ray variability of IRAS 13224-3809-I. The variability process - Accepted Manuscript
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Accepted/In Press date: 13 September 2018
e-pub ahead of print date: 14 September 2018
Published date: January 2019

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Local EPrints ID: 427883
URI: https://eprints.soton.ac.uk/id/eprint/427883
ISSN: 0035-8711
PURE UUID: 59a4507e-8b8c-4d74-aafa-986e292b9f34

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Date deposited: 01 Feb 2019 17:30
Last modified: 13 Mar 2019 17:36

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Contributors

Author: W.N. Alston
Author: A.C. Fabian
Author: D.J.K. Buisson
Author: E. Kara
Author: M.L. Parker
Author: A.M. Lohfink
Author: P. Uttley
Author: D.R. Wilkins
Author: C. Pinto
Author: B. De Marco
Author: E.M. Cackett
Author: M.J. Middleton
Author: D.J. Walton
Author: C.S. Reynolds
Author: J. Jiang
Author: L.C. Gallo
Author: A. Zogbhi
Author: G. Miniutti
Author: M. Dovciak
Author: A.J. Young

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