Correlated X-ray/ultraviolet/optical variability and the nature of accretion disc in the bare Seyfert 1 galaxy Fairall 9

Pal, Main; Dewangan, G. C.; Connolly, S.; Misra, Ranjeev

doi:10.1093/mnras/stw3173

Cited by 25 publications

(23 citation statements)

References 63 publications

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“…In such cases, available light curves to date can not be used for the analysis due to jet dominated emission. We used JAVELIN code (Zu et al 2011) to estimate the lag following the procedures described in and Pal et al (2017). We found time-lag of ∼ 3-day and ∼ 16-day for UVW1 compared to Xrays (see Fig.…”

Section: Timing Analysismentioning

confidence: 99%

Strong Soft X-Ray Excess in 2015 XMM-Newton Observations of BL Lac OJ 287

Pal

Kushwaha

Dewangan

et al. 2020

ApJ

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We report a strong soft X-ray excess in the BL-Lacartae γ-ray blazar OJ 287 during the long exposure in May 2015, amongst two of the latest XMM-Newton observations performed in May 2015 and 2018. In case of May 2015 observation, a logparabola model fits the EPIC-pn data well while a logparabola plus powerlaw describes the overall simultaneous optical to X-ray spectra, suggesting the excess as the synchrotron tail. This interpretation, however, is inconsistent with the observed spectral break between near-infrared and optical spectra, attributed to standard disk around a supermassive black hole (SMBH). Based on this, we considered two commonly invoked accretion disk based models in AGNs to explain the soft excess: the cool Comptonization component in the accretion disk and the blurred reflection from the partially ionized accretion disk. We found that both cool Comptonization and blurred reflection models provide equally good fit to the data and favor a super-heavy SMBH of mass ∼ 10 10 M ⊙ . Further investigation of about a month long simultaneous X-ray and UV pointing observations revealed a delayed UV emission with respect to the 1.5-10 keV band, favoring X-ray reprocessing phenomenon as the dominant mechanism. The results suggest that the soft excess is probably caused by strong light bending close to the SMBH. The detected soft excess in 2015 data and its disappearance in 2018 data is also consistent with the presence of accretion disk emission, inferred from the NIR-optical spectral break between

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Section: Timing Analysismentioning

confidence: 99%

Strong Soft X-Ray Excess in 2015 XMM-Newton Observations of BL Lac OJ 287

Pal

Kushwaha

Dewangan

et al. 2020

ApJ

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“…This is the equivalent to the disks being too big (the lag too large) by a factor of 1.6 based on the observed flux compared to the accretion disk model. More recently, observations of NGC2617 (Shappee et al 2014), NGC3516 (Noda et al 2016), NGC6814 (Troyer et al 2016), Fairall9 (Pal et al 2017), Ark120 (Gliozzi et al 2017), and a sample of 21 AGNs in the Swift archive (Buisson et al 2017) all find lags that are longer than expected for a standard thin disk. Both Pan-STARRS and the Dark Energy Survey (DES) are obtaining light curves of quasars in multiple photometric bands, allowing for determination of the average sizes from a large number of objects (Jiang et al 2017;Mudd et al 2017).…”

Section: Introductionmentioning

confidence: 97%

Accretion Disk Reverberation with Hubble Space Telescope Observations of NGC 4593: Evidence for Diffuse Continuum Lags

Cackett

Chiang

McHardy

et al. 2018

ApJ

133

186

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The Seyfert 1 galaxy NGC 4593 was monitored spectroscopically with the Hubble Space Telescope as part of a reverberation mapping campaign that also included Swift, Kepler, and ground-based photometric monitoring. During 2016 July 12-August 6, we obtained 26 spectra across a nearly continuous wavelength range of ∼1150-10000 Å. These were combined with Swift data to produce a UV/optical "lag spectrum," which shows the interband lag relative to the Swift UVW2 band as a function of wavelength. The broad shape of the lag spectrum appears to follow the τ ∝ λ 4/3 relation seen previously in photometric interband lag measurements of other active galactic nuclei (AGNs). This shape is consistent with the standard thin disk model, but the magnitude of the lags implies a disk that is a factor of ∼3 larger than predicted, again consistent with what has been previously seen in other AGNs. In all cases these large disk sizes, which are also implied by independent gravitational microlensing of higher-mass AGNs, cannot be simply reconciled with the standard model. However, the most striking feature in this higher-resolution lag spectrum is a clear excess around the 3646 Å Balmer jump. This strongly suggests that diffuse emission from gas in the much larger broad-line region (BLR) must also contribute significantly to the interband lags. While the relative contributions of the disk and BLR cannot be uniquely determined in these initial measurements, it is clear that both will need to be considered to comprehensively model and understand AGN lag spectra.

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“…There are a number of possible explanations for this increased lag, including that the lag corresponds to the thermal timescale due to the thermal reverberation from a significantly hot disc with low accretion rate (Kammoun et al 2019;Sun et al 2018), hot accretion flow with a disc truncation (Noda et al 2016), very large area of the reprocessing site (Pal et al 2017;Pal and Naik 2018), non-blackbody nature of the emerging disc spectra due to the low atmospheric density (Hall et al 2018). Other potential explanations include that the X-rays do not directly illuminate the outer disc but are first reprocessed by, and scattered through, the scattering atmosphere (Narayan 1996), the inflated inner edge of the accretion disc, which introduces an additional lag (Gardener and Done 2017).…”

Section: Introductionmentioning

confidence: 99%

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

Pahari

McHardy

Vincentelli

et al. 2020

Monthly Notices of the Royal Astronomical Society

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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.

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Correlated X-ray/ultraviolet/optical variability and the nature of accretion disc in the bare Seyfert 1 galaxy Fairall 9

Cited by 25 publications

References 63 publications

Strong Soft X-Ray Excess in 2015 XMM-Newton Observations of BL Lac OJ 287

Strong Soft X-Ray Excess in 2015 XMM-Newton Observations of BL Lac OJ 287

Accretion Disk Reverberation with Hubble Space Telescope Observations of NGC 4593: Evidence for Diffuse Continuum Lags

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

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