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

Abstract

Using a month-long X-ray lightcurve from $RXTE$/PCA and 1.5 month long UV continuum lightcurves from $IUE$ spectra in 1220$-$1970 $\mathring{A}$, 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 $\mathring{A}$ by 3.49 $\pm$ 0.22 days which is possibly caused by either propagating fluctuation or variable comptonisation. However, if variations slower than 5 days are removed from the X-ray lightcurve, the UV variations then lag behind the X-rays variations by 0.37$\pm$0.14 day, 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 lightcurves. Continuum lightcurves 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 days, the slow variations at 1825 $\mathring{A}$ lag those at 1315 $\mathring{A}$ by $0.29\pm 0.06$ day, while the fast variations are coincident ($0.04\pm 0.12$ day). The UV/optical continuum reverberation lag from $IUE$, $Swift$ and other optical telescopes at different wavelengths are consistent with the relationship: $\tau \propto {\lambda }^{4/3}$, predicted for the standard accretion disc theory while the best-fit X-ray delay from $RXTE$ and $Swift$/XRT shows a negative X-ray offset of $\sim$0.38 days from the standard disc delay prediction.

13 pages, 9 figures, 1 table, accepted for publication in MNRAS

References in corpus (11)

• The AGN Black Hole Mass Database
• Space Telescope and Optical Reverberation Mapping Project. II. Swift and HST Reverberation Mapping of the Accretion Disk of NGC 5548
• Testing thermal reprocessing in AGN accretion discs
• Quasar Accretion Disks Are Strongly Inhomogeneous
• Swift monitoring of NGC 5548: X-ray reprocessing and short term UV/optical variability
• Correlated X-ray/Optical Variability in the Quasar MR2251-178
• Space Telescope and Optical Reverberation Mapping Project VI: reverberating Disk Models for NGC 5548
• Reverberation Mapping of the Seyfert 1 Galaxy NGC 7469
• A hard look at thermal reverberation and optical/UV lags in NGC 5548
• Correlated X-ray and Optical Variability in Mkn 509
• Correlated X-ray/UV/optical variability and the nature of accretion disc in the bare Seyfert 1 galaxy Fairall~9

Cited by in corpus (11)

• Modeling the UV/optical continuum time-lags in AGN
• On the multi-wavelength variability of Mrk 110: Two components acting at different timescales
• Reverberation Mapping Measurements of Black Hole Masses and Broad-Line Region Kinematics in Mrk 817 and NGC 7469
• Revisiting UV/optical continuum time lags in AGN
• The luminosity-dependent contribution from the broad line region to the wavelength-dependent lags in Mrk 110
• Broadband X-ray/UV/optical time-resolved spectroscopy of NGC 5548: The origin of the UV/optical variability in active galactic nuclei
• Contrasting X-ray/UV time-lags in Seyfert 1 galaxies NGC 4593 and NGC 7469 using AstroSat observations
• AGN Light Echoes and the Accretion Disc Self-Gravity Limit
• The Relation between X-ray and Ultraviolet Variability of Quasars
• The evolution of the UV/optical lag spectrum of NGC 7469 seen by the Liverpool Telescope
• Timescale-dependent X-ray to UV time lags of NGC 4593 using high-intensity XMM-Newton observations with Swift and AstroSat