X-ray Reverberation Mapping of Ark 564 using Gaussian Process Regression

Collin D. Lewin, Erin Kara, Daniel R. Wilkins, Guglielmo Mastroserio, Javier A. García, Rachel Zhang, William Alston, Riley M. Connors, Thomas Dauser, Andy C. Fabian, Adam Ingram, Jiachen Jiang, Anne M. Lohfink, Matteo Lucchini, Christopher S. Reynolds, Francesco Tombesi, Michiel van der Klis, Jingyi Wang

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Ark 564 is an extreme high-Eddington Narrow-line Seyfert 1 galaxy, known for being one of the brightest, most rapidly variable soft X-ray AGN, and for having one of the lowest temperature coronae. Here we present a 410-ks NuSTAR observation and two 115-ks XMM-Newton observations of this unique source, which reveal a very strong, relativistically broadened iron line. We compute the Fourier-resolved time lags by first using Gaussian processes to interpolate the NuSTAR gaps, implementing the first employment of multi-task learning for application in AGN timing. By fitting simultaneously the time lags and the flux spectra with the relativistic reverberation model RELTRANS, we constrain the mass at $2.3^{+2.6}_{-1.3} \times 10^6M_\odot$, although additional components are required to describe the prominent soft excess in this source. These results motivate future combinations of machine learning, Fourier-resolved timing, and the development of reverberation models.
Original languageUndefined/Unknown
JournalAstrophysical Journal Letters
Publication statusPublished - 11 Nov 2022


  • astro-ph.HE

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