Modeling the Multiwavelength Variability of Mrk 335 Using Gaussian Processes

Abstract

The optical and UV variability of the majority of active galactic nuclei may be related to the reprocessing of rapidly changing X-ray emission from a more compact region near the central black hole. Such a reprocessing model would be characterized by lags between X-ray and optical/UV emission due to differences in light travel time. Observationally, however, such lag features have been difficult to detect due to gaps in the lightcurves introduced through factors such as source visibility or limited telescope time. In this work, Gaussian process regression is employed to interpolate the gaps in the Swift X-ray and UV lightcurves of the narrow-line Seyfert 1 galaxy Mrk 335. In a simulation study of five commonly employed analytic Gaussian process kernels, we conclude that the Matern 1 2 and rational quadratic kernels yield the most well-specified models for the X-ray and UVW2 bands of Mrk 335. In analyzing the structure functions of the Gaussian process lightcurves, we obtain a broken power law with a break point at 125 days in the UVW2 band. In the X-ray band, the structure function of the Gaussian process lightcurve is consistent with a power law in the case of the rational quadratic kernel while a broken power law with a break point at 66 days is obtained from the Matern 1 2 kernel. The subsequent cross-correlation analysis is consistent with previous studies and furthermore shows tentative evidence for a broad X-ray-UV lag feature of up to 30 days in the lag-frequency spectrum where the significance of the lag depends on the choice of Gaussian process kernel.Unified Astronomy Thesaurus concepts: Accretion (14); Galaxy accretion disks (562); Active galaxies (17); Gaussian Processes regression (1930); Bayesian statistics (1900); Galaxy nuclei (609)

Frequency-resolved lags in UV/optical continuum reverberation mapping

“…In the UV many of the lags outside the lowest frequency are consistent with zero. This is similar to the findings of Griffiths et al (2021) who look at the lag between X-rays and UVW2 in Mrk 335, only finding tentative evidence for non-zero lags in the lowest frequency bins.…”

“…However, there has not been a study of the cross-spectrum and frequency-resolved lags in AGN light curves across the full UV/optical range. The only previous attempt compared the X-ray and UV light curves in Mrk 335, and only saw tentative lags on long timescales, with all values consistent with zero within 2σ (Griffiths et al 2021).…”

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

“…More recently, Gaussian process regression (GPR) has grown in popularity and has shown success in modeling the underlying probability distribution of sparse light curves of asteroids (Willecke Lindberg et al 2021), AGN (Kelly et al 2014;Wilkins 2019;Griffiths et al 2021), and stars (Brewer & Stello 2009;Czekala et al 2017;McAllister et al 2017). Continuous realizations of the light curve can then be generated after modeling the observed variability, allowing for a probabilistic treatment of data generated in the gaps.…”

Effect of non-resonant background on the extraction of Raman signals from CARS spectra using deep neural networks

“…In particular, it has successfully modelled 1D time series and spectral data and learned kernels having an extractable power spectral density. 55 Further, nonstationary kernels achieved via input warping 44 can also be useful for modelling the nonstationary behaviour of intensity as a function of Raman shi.…”