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On Uncertainties in Cross-Correlation Lags and the Reality of Wavelength-Dependent Continuum Lags in Active Galactic Nuclei

7 Pith papers cite this work. Polarity classification is still indexing.

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abstract

We describe a model-independent method of assessing the uncertainties in cross-correlation lags determined from AGN light curves, and use this method to investigate the reality of lags between UV and optical continuum variations in well-studied AGNs. Our results confirm the existence of such lags in NGC 7469. We find that the continuum variations at 1825 A, 4845 A, and 6962 A follow those at 1315A by 0.22^{+0.12}_{-0.13} days, 1.25^{+0.48}_{-0.35} days, and 1.84^{+0.93}_{-0.94} days, respectively, based on the centroids of the cross-correlation functions; the error intervals quoted correspond to 68% confidence levels, and each of these lags is greater than zero at no less than 97% confidence. We do not find statistically significant interband continuum lags in NGC 5548, NGC 3783, or Fairall 9. Wavelength-dependent continuum lags may be marginally detected in the case of NGC 4151. However, on the basis of theoretical considerations, wavelength-dependent continuum lags in sources other than NGC 7469 are not expected to have been detectable in previous experiments. We also confirm the existence of a statistically significant lag between X-ray and UV continuum variations in the blazar PKS 2155-304.

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2026 7

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UNVERDICTED 7

representative citing papers

Radiation-pressure instability is an artifact of constant-$\alpha$ closure

astro-ph.HE · 2026-06-30 · unverdicted · novelty 5.0

Requiring thermal stability and single-valuedness in the thin-disk Ṁ-Σ plane produces a viscosity law α(X) with X = P_gas/P_rad that eliminates the radiation-pressure dominated instability while preserving the effective-temperature profile.

Time lags as proxy of spectral evolution in gamma-ray bursts

astro-ph.HE · 2026-06-09 · unverdicted · novelty 5.0

Time lags between energy bands serve as proxies for spectral evolution in GRBs, with positive lags tracing prompt emission softening and negative lags indicating a new delayed high-energy component.

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