Timescale-dependent X-ray to UV time lags of NGC 4593 using high-intensity XMM-Newton observations with Swift and AstroSat

Abstract

We present a 140ks observation of NGC 4593 with XMM-Newton providing simultaneous and continuous PN X-ray and OM UV (UVW1 2910Å) lightcurves which sample short-timescale variations better than previous observations. These observations were simultaneous with 22d of Swift X-ray and UV/optical monitoring, reported previously, and 4d of AstroSat X-ray (SXT), far (FUV 1541Å), and near (NUV 2632Å) UV allowing lag measurements between them and the highly-sampled XMM. From the XMM we find that UVW1 lags behind the X-rays by 29.5$\pm$1.3ks, $\sim$half the lag previously determined from the Swift monitoring. Re-examination of the \textit{Swift} data reveals a bimodal lag distribution, with evidence for both the long and short lags. However if we detrend the Swift lightcurves by LOWESS filtering with a 5d width, only the shorter lag (23.8$\pm$21.2ks) remains. The NUV observations, compared to PN and SXT, confirm the $\sim$30ks lag found by XMM and, after 4d filtering is applied to remove the long-timescale component, the FUV shows a lag of $\sim$23ks. The resultant new UVW1, FUV, and NUV lag spectrum extends to the X-ray band without requiring additional X-ray to UV lag offset, which if the UV arises from reprocessing of X-rays, implies direct illumination of the reprocessor. By referencing previous Swift and HST lag measurements, we obtain an X-ray to optical lag spectrum which agrees with a model using the KYNreverb disc-reprocessing code, assuming the accepted mass of $7.63\times 10^6{M}_{\odot }$ and a spin approaching maximum. Previously noted lag contribution from the BLR in the Balmer and Paschen continua are still prominent.

arXiv comment13 pages, 23 figures

References in corpus (31)

• The Man Behind the Curtain: X-rays Drive the UV through NIR Variability in the 2013 AGN Outburst in NGC 2617
• On Uncertainties in Cross-Correlation Lags and the Reality of Wavelength-Dependent Continuum Lags in Active Galactic Nuclei
• Reverberation Measurements of the Inner Radius of the Dust Torus in Nearby Seyfert 1 Galaxies
• Investigating a Fluctuating-accretion Model for the Spectral-timing Properties of Accreting Black Hole Systems
• Is Quasar Optical Variability a Damped Random Walk?
• 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
• The Sizes of the X-ray and Optical Emission Regions of RXJ1131-1231
• In-orbit Calibrations of the Ultra-Violet Imaging Telescope
• On the Reliability of Cross Correlation Function Lag Determinations in Active Galactic Nuclei
• The First Swift Intensive AGN Accretion Disk Reverberation Mapping Survey
• Swift monitoring of NGC 5548: X-ray reprocessing and short term UV/optical variability
• Accretion disk reverberation with Hubble Space Telescope observations of NGC 4593: evidence for diffuse continuum lags
• The Variable Diffuse Continuum Emission of Broad Line Clouds
• Additional Calibration of the Ultra-Violet Imaging Telescope on board AstroSat
• Correlated long-term optical and X-ray variations in NGC 5548
• Modelling the broad Fe Kα reverberation in the AGN NGC 4151
• The Structure of the X-ray and Optical Emitting Regions of the Lensed Quasar Q 2237+0305
• The origin of the UV/optical lags in NGC 5548
• X-ray/UV/optical variability of NGC 4593 with Swift: Reprocessing of X-rays by an extended reprocessor
• General relativistic modelling of the negative reverberation X-ray time delays in AGN
• New constraints on the continuum-emission mechanism of AGN: Intensive monitoring of NGC 7469 in the X-ray and ultraviolet
• Quantifying the impact of variable BLR diffuse continuum contributions on measured continuum inter-band delays
• Long term optical and X-ray variability of the Seyfert galaxy Markarian 79
• Correlation and time delays of the X-ray and optical emission of the Seyfert Galaxy NGC3783
• Twelve years of X-ray and optical variability in the Seyfert galaxy NGC 4051
• UV/optical disk thermal reverberation in AGN: an in-depth study with an analytic prescription for the time-lag spectra
• On the multi-wavelength variability of Mrk 110: Two components acting at different timescales
• Correlated X-ray/Ultraviolet/Optical variability in the very low mass AGN NGC 4395
• Evidence for variability timescale dependent UV/X-ray delay in Seyfert 1 AGN NGC 7469
• The luminosity-dependent contribution from the broad line region to the wavelength-dependent lags in Mrk 110

Cited by in corpus (1)

• Contrasting X-ray/UV time-lags in Seyfert 1 galaxies NGC 4593 and NGC 7469 using AstroSat observations