Multiwavelength power-spectrum analysis of NGC 5548

Abstract

NGC 5548 was recently monitored intensively from NIR to X-rays as part of the STORM campaign. Its disc emission was found to lag behind the observed X-rays, while the measured time lag was increasing with wavelength. These results are consistent with the assumption that short term variability in AGN emission is driven by the X-ray illumination of the accretion disc. In this work, we studied the power spectrum of UV/optical and X-ray emission of NGC 5548, using the data of the STORM campaign as well as previous Swift data, in order to investigate the relation between the UV/optical and X-ray variability and to examine its consistency with the above picture. We demonstrate that even the power spectrum results are compatible with a standard disc being illuminated by X-rays, with low accretion rates, but the details are not entirely consistent with the results from the modelling of the "τ vs λ" relation. The differences indicate that the inner disc might be covered by a "warm corona" which does not allow the detection of UV/optical emission from the inner disc. Finally, we found strong evidence that the UV emission of NGC 5548 is not stationary.

11 pages, 7 figures, in press by MNRAS

References in corpus (12)

• 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
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• A fast and long-lived outflow from the supermassive black hole in NGC 5548
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• Swift monitoring of NGC 5548: X-ray reprocessing and short term UV/optical variability
• Space Telescope and Optical Reverberation Mapping Project VI: reverberating Disk Models for NGC 5548
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• Corona-Heated Accretion-disk Reprocessing (CHAR): A Physical Model to Decipher the Melody of AGN UV/optical Twinkling
• A hard look at thermal reverberation and optical/UV lags in NGC 5548
• A deep X-ray view of the bare AGN Ark120. V. Spin determination from disc-Comptonisation efficiency method
• X-ray, UV and optical time delays in the bright Seyfert galaxy Ark 120 with co-ordinated Swift and ground-based observations

Cited by in corpus (13)

• Modeling the UV/optical continuum time-lags in AGN
• UV/optical disk thermal reverberation in AGN: an in-depth study with an analytic prescription for the time-lag spectra
• Frequency-resolved lags in UV/optical continuum reverberation mapping
• A physical model for the broadband energy spectrum of X-ray illuminated accretion discs: fitting the spectral energy distribution of NGC 5548
• Self-lensing flares from black hole binaries II: observing black hole shadows via light-curve tomography
• Explaining the moderate UV/X-ray correlation in AGN
• Revisiting UV/optical continuum time lags in AGN
• A physical model for the UV/optical power spectra of AGN
• X-ray/UVOIR Frequency-resolved Time Lag Analysis of Mrk 335 Reveals Accretion Disk Reprocessing
• Broadband X-ray/UV/optical time-resolved spectroscopy of NGC 5548: The origin of the UV/optical variability in active galactic nuclei
• X-ray illuminated accretion discs and quasar microlensing disc sizes
• X-ray reverberation modelling of the continuum, optical/UV time-lags in quasars
• The first X-ray look at SMSS J114447.77-430859.3: the most luminous quasar in the last 9 Gyr