Evidence for variability time-scale-dependent UV/X-ray delay in Seyfert 1 AGN NGC 7469

Mayukh Pahari*, Ian M. McHardy, Federico Vincentelli, Edward M. Cackett, Bradley M. Peterson, Michael R. Goad, Kayhan Gültekin, Keith Horne

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

27 Citations (Scopus)
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Abstract

Using a month-long X-ray light curve from RXTE/PCA and 1.5 month-long UV continuum light curves from IUE spectra in 1220-1970 Å, we performed a detailed time-lag study of the Seyfert 1 galaxy NGC 7469. Our cross-correlation analysis confirms previous results showing that the X-rays are delayed relative to the UV continuum at 1315 Å by 3.49 ± 0.22 d, which is possibly caused by either propagating fluctuation or variable Comptonization. However, if variations slower than 5 d are removed from the X-ray light curve, the UV variations then lag behind the X-ray variations by 0.37 ± 0.14 d, consistent with reprocessing of the X-rays by a surrounding accretion disc. A very similar reverberation delay is observed between Swift/XRT X-ray and Swift/UVOT UVW2, U light curves. Continuum light curves extracted from the Swift/GRISM spectra show delays with respect to X-rays consistent with reverberation. Separating the UV continuum variations faster and slower than 5 d, the slow variations at 1825 Å lag those at 1315 Å by 0.29 ± 0.06 d, while the fast variations are coincident (0.04 ± 0.12 d). The UV/optical continuum reverberation lag from IUE, Swift, and other optical telescopes at different wavelengths are consistent with the relationship: τ ∝  λ4/3, predicted for the standard accretion disc theory while the best-fitting X-ray delay from RXTE and Swift/XRT shows a negative X-ray offset of ∼0.38 d from the standard disc delay prediction.

Original languageEnglish
Pages (from-to)4057-4068
Number of pages12
JournalMonthly Notices of the Royal Astronomical Society
Volume494
Issue number3
Early online date21 Apr 2020
DOIs
Publication statusPublished - May 2020

Keywords

  • Accretion, accretion discs
  • Black hole physics
  • Galaxies: individual: NGC 7469
  • Galaxies: Seyfert
  • X-rays: galaxies

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