X-Ray Reverberation Mapping of Ark 564 Using Gaussian Process Regression

Lewin, Collin; Kara, Erin; Wilkins, D. R.; Mastroserio, Guglielmo; Garcia, J. Rodriguez; Zhang, Rachel C.; Alston, W. N.; Connors, Riley; Dauser, Robert C.; Fabian, A. C.; Ingram, Adam; Jiang, Jiachen; Lohfink, A.; Lucchini, Matteo; Reynolds, C. S.; Tombesi, Francesco; Klis, M. van der; Wang, Jingyi

doi:10.3847/1538-4357/ac978f

Cited by 5 publications

(8 citation statements)

References 71 publications

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“…The difference in kernel form for modeling only these two bands could result from the higher signal-to-noise in these two bands as shown in Figure 1. These results are generally consistent with previous kernel comparisons for modeling AGN variability, as Wilkins (2019), Griffiths et al (2021), and Lewin et al (2022) all find the RQ and Matérn-1 2 kernels to perform statistically similar. Similar to the three aforementioned works, we find the SE kernel provides the poorest description of the observed light curves.…”

Section: Selecting the Kernel Functionsupporting

confidence: 89%

“…One must assume the data are normally distributed as well as a functional form for the kernel function, which we discuss in the following Sections (3.1 and 3.2, respectively). The choice of kernel function form has been found to impact the significance of lag recovery depending on the data sampling rate (Griffiths et al 2021;Lewin et al 2022). Each functional form has its own set of hyperparameters θ, each encoding a different aspect of the variability, such as length scales (timescales, in our case), amplitudes, etc.…”

Section: Fourier-resolved Timing Using Gpsmentioning

confidence: 99%

“…We consider the same three common forms for the kernel function as those assessed to describe AGN variability by Wilkins (2019), Griffiths et al (2021), and Lewin et al (2022): the squared exponential (SE), rational quadratic (RQ), and Matérn kernels. We refer to Wilkins (2019) for an introduction to these functional forms.…”

Section: Selecting the Kernel Functionmentioning

confidence: 99%

“…GPs have been shown to be successful in modeling AGN variability via the faithful reproduction of underlying autocorrelation functions (Wilkins 2019;Griffiths et al 2021). Most pertinent for this work is the efficacy of GPs in preserving phase/cross-correlation information between light curves: the recovery of time lags within a fractional error of a few percent has been shown using both simulations and real data (Wilkins 2019;Lewin et al 2022).…”

Section: Introductionmentioning

confidence: 97%

“…Many even questioned whether GPs would replace this fundamental ML architecture (MacKay 1998), given the more interpretable nature of GPs (e.g., the kernel/ covariance function hyperparameters in a GP correspond to intuitive properties of the data, such as variability length scales and amplitudes). In the astrophysics community, the use of GPs has been growing in popularity for regression applications to sparse light curves of asteroids (Willecke Lindberg et al 2021), stars (Brewer & Stello 2009;Czekala et al 2017), and AGNs (Kelly et al 2014;Wilkins 2019;Griffiths et al 2021;Lewin et al 2022), and for generative modeling (e.g., quasar spectra; Eilers et al 2022). GPs have been shown to be successful in modeling AGN variability via the faithful reproduction of underlying autocorrelation functions (Wilkins 2019;Griffiths et al 2021).…”

Section: Introductionmentioning

confidence: 99%

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X-Ray/UVOIR Frequency-resolved Time Lag Analysis of Mrk 335 Reveals Accretion Disk Reprocessing

Lewin,

Kara,

Cackett

et al. 2023

ApJ

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UV and optical continuum reverberation mapping is a powerful tool for probing the accretion disk and inner broad-line region. However, recent reverberation mapping campaigns in the X-ray, UV, and optical have found lags consistently longer than those expected from the standard disk reprocessing picture. The largest discrepancy to date was recently reported in Mrk 335, where UV/optical lags are up to 12 times longer than expected. Here, we perform a frequency-resolved time lag analysis of Mrk 335, using Gaussian processes to account for irregular sampling. For the first time, we compare the Fourier frequency-resolved lags directly to those computed using the popular interpolated cross-correlation function method applied to both the original and detrended light curves. We show that the anticipated disk reverberation lags are recovered by the Fourier lags when zeroing in on the short-timescale variability. This suggests that a separate variability component is present on long timescales. If this separate component is modeled as reverberation from another region beyond the accretion disk, we constrain a size scale of roughly 15 lt-days from the central black hole. This is consistent with the size of the broad-line region inferred from Hβ reverberation lags. We also find tentative evidence for a soft X-ray lag, which we propose may be due to light travel time delays between the hard X-ray corona and distant photoionized gas that dominates the soft X-ray spectrum below 2 keV.

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Section: Selecting the Kernel Functionsupporting

confidence: 89%

Section: Fourier-resolved Timing Using Gpsmentioning

confidence: 99%

Section: Selecting the Kernel Functionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

X-Ray/UVOIR Frequency-resolved Time Lag Analysis of Mrk 335 Reveals Accretion Disk Reprocessing

Lewin,

Kara,

Cackett

et al. 2023

ApJ

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A theoretical Fourier-transformation model for the formation of X-ray time lags from black hole accretion discs

Mahapol,

Becker

2024

Monthly Notices of the Royal Astronomical Society

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X-ray emission from active galactic nuclei (AGNs) often displays complex and rapid variability, which may provide a glimpse into the detailed thermal and dynamical structure of the accreting gas near the event horizon of the central black hole. The observed variability can be analyzed using Fourier transforms of the light curves in multiple energy channels, which can be used to generate Fourier phase lags, corresponding to lags in the time domain. The X-ray time lags may be either soft lags or hard lags, depending on whether the variability in the hard energy channel precedes that in the soft channel or vice versa. The physical explanation for the observed X-ray time lags from AGNs has been puzzling, and several scenarios have been proposed. In this paper, we explore the hypothesis that the X-ray time lags are produced as a result of the reprocessing of iron L-line and K-line seed photons generated via fluorescence, which is driven by a variable incident radiation field. The seed photons are reprocessed by a combination of thermal and bulk Comptonization and spatial reverberation. We assume that the inner region of the accretion flow can be approximated as a hot, geometrically thick ADAF disc. The outer radius of the ADAF region is equal to the shock formation radius, which is located just outside the centrifugal barrier. The time-dependent radiative transfer in the disc is analyzed using a Fourier-transformed, vertically-averaged transport equation in cylindrical coordinates. We demonstrate that the new model can successfully reproduce the complex X-ray variability data for the Seyfert 1 galaxies 1H 0707-495 and Ark 564.

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The high energy X-ray probe (HEX-P): probing the physics of the X-ray corona in active galactic nuclei

Kammoun,

Lohfink,

Masterson

et al. 2024

Front. Astron. Space Sci.

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The hard X-ray emission in active galactic nuclei (AGN) and black hole X-ray binaries is thought to be produced by a hot cloud of electrons referred to as the corona. This emission, commonly described by a power law with a high-energy cutoff, is suggestive of Comptonization by thermal electrons. While several hypotheses have been proposed to explain the origin, geometry, and composition of the corona, we still lack a clear understanding of this fundamental component. NuSTAR has been playing a key role improving our knowledge of X-ray coronæ thanks to its unprecedented sensitivity above 10 keV. However, these constraints are limited to bright, nearby sources. The High Energy X-ray Probe (HEX-P) is a probe-class mission concept combining high spatial resolution X-ray imaging and broad spectral coverage (0.2–80 keV) with a sensitivity superior to current facilities. In this paper, we highlight the major role that HEX-P will play in further advancing our insights of X-ray coronæ notably in AGN. We demonstrate how HEX-P will measure key properties and track the temporal evolution of coronæ in unobscured AGN. This will allow us to determine their electron distribution and test the dominant emission mechanisms. Furthermore, we show how HEX-P will accurately estimate the coronal properties of obscured AGN in the local Universe, helping address fundamental questions about AGN unification. In addition, HEX-P will characterize coronæ in a large sample of luminous quasars at cosmological redshifts for the first time and track the evolution of coronæ in transient systems in real time. We also demonstrate how HEX-P will enable estimating the coronal geometry using spectral-timing techniques. HEX-P will thus be essential to understand the evolution and growth of black holes over a broad range of mass, distance, and luminosity, and will help uncover the black holes’ role in shaping the Universe.

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X-Ray Reverberation Mapping of Ark 564 Using Gaussian Process Regression

Cited by 5 publications

References 71 publications

X-Ray/UVOIR Frequency-resolved Time Lag Analysis of Mrk 335 Reveals Accretion Disk Reprocessing

X-Ray/UVOIR Frequency-resolved Time Lag Analysis of Mrk 335 Reveals Accretion Disk Reprocessing

A theoretical Fourier-transformation model for the formation of X-ray time lags from black hole accretion discs

The high energy X-ray probe (HEX-P): probing the physics of the X-ray corona in active galactic nuclei

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