Recent intense X-ray and UV monitoring campaigns with Swift have detected clear UV lags behind X-ray in several local active galactic nuclei (AGNs). The UV to X-ray lags are often larger (by a factor up to ~ 20) than expected if the UV variation is simply due to the X-ray reprocessing. We previously developed a model in which the UV/optical variations are attributed to disk turbulences, and the effect of large-scale turbulence is considered. Our model, which overcomes many severe challenges to the reprocessing scheme, can well explain the observed variations in NGC 5548, particularly the correlations and lags among the UV/optical bands. In this work, assuming the corona heating is associated with turbulences in the inner accretion disk, we extend our study to model the correlations and lags between the X-ray and UV/optical bands. We find that our model, without the need of light echoing, can well reproduce the observed UV to X-ray lags and the optical to UV lags simultaneously in four local Seyfert galaxies, including NGC 4151, NGC 4395, NGC 4593, and NGC 5548. In our scenario, relatively larger UV to X-ray lag is expected for AGN with smaller innermost disk radius and thus more compact corona. Interestingly, for these Seyfert galaxies studied in this work, sources with relatively larger UV to X-ray lags do have broader Fe Ka lines, indicative of relativistic broadening due to more compact corona and smaller innermost disk radius. If confirmed with more X-ray and UV monitoring campaigns, this interesting discovery would provide a new probe to the inner disk/corona.

https://iopscience.iop.org/article/10.3847/1538-4357/ab7991/pdf

EUCLIA. II. On the Puzzling Large UV to X-Ray Lags in Seyfert Galaxies

Optical Fe II emission is a strong feature in quasar spectra originating in the broad-line region (BLR). The difficulty in understanding the complex Fe II pseudo-continuum has led us to search for other reliable, simpler ionic species such as Ca II. In this first part of the series, we confirm the strong correlation between the strengths of two emission features, the optical Fe II and the NIR Ca II, both from observations and photoionization modelling. With the inclusion of an up-to-date compilation of observations with both optical Fe II and NIR Ca II measurements, we span a wider and more extended parameter space and confirm the common origin of these two spectral features with our photoionization models using CLOUDY. Taking into account the effect of dust into our modelling, we constrain the BLR parameter space (primarily, in terms of the ionization parameter and local cloud density) as a function of the strengths of Fe II and Ca II emission.

The CaFe Project: Optical Fe II and Near-Infrared Ca II triplet emission in active galaxies: (I) Photoionization modelling

Optical Fe II emission is a strong feature of quasar spectra originating in the broad-line regions (BLRs). The difficulty in understanding the complex Fe II pseudo-continuum has led us in search of other reliable, simpler ionic species such as Ca II. In this first part of the series, we confirm the strong correlation between the strengths of two emission features, the optical Fe II and the NIR Ca II, both from observations and photoionization modelling. With the inclusion of an up-to-date compilation of observations with both optical Fe II and NIR Ca II measurements, we span a wider and more extended parameter space and confirm the common origin of these two species with our photoionization models using CLOUDY. Taking into account the effect of dust into our modelling, we retrieve the log U - log n parameter space as a function of the strengths of Fe II and Ca II emission. Incorporating a broad range of metallicity and extended cloud columns we reinstate this correlation and explain the emission from the strong Fe II emitting Narrow-Line Seyfert 1 galaxies (NLS1s).

Optical Fe II and Near-Infrared Ca II triplet emission in active galaxies: (I) Photoionization modelling

The study of the broad-line region (BLR) using reverberation mapping has allowed us to establish an empirical relation between the size of this line-emitting region and the continuum luminosity that drives the line emission (i.e., the R Hβ − L5100 relation). To realize its full potential, the intrinsic scatter in the R Hβ − L5100 relation needs to be understood better. The mass accretion rate (or equivalently the Eddington ratio) plays a key role in addressing this problem. On the other hand, the Eigenvector 1 schema has helped to reveal an almost clear connection between the Eddington ratio and the strength of the optical Fe II emission that originates from the BLR. This article aims to reveal the connection between theoretical entities, such as the ionization parameter (U) and cloud mean density (nH) of the BLR, with physical observables obtained directly from the spectra, such as optical Fe II strength (R FeII ) that has shown immense potential to trace the accretion rate. We utilize the photoionization code CLOUDY and perform a suite of models to reveal the physical conditions in the low-ionization, dust-free, line-emitting BLR. The key here is the focus on the recovery of the equivalent widths (EWs) for the two low-ionization emission lines—Hβ and the optical Fe II—in addition to the ratio of their EWs, i.e., R FeII . We compare the spectral energy distributions, I Zw 1 and NGC 5548, of prototypical Population A and Population B sources, respectively, in this study. The results from the photoionization modeling are then combined with the existing reverberation-mapped sources with observed R FeII estimates taken from the literature, thus allowing us to assess our analytical formulation to tie together the aforementioned quantities. The recovery of the correct physical conditions in the BLR then suggests that—the BLR “sees” only a very small fraction (∼1–10%) of the original ionizing continuum.

Parameterizing the AGN Radius–Luminosity Relation from the Eigenvector 1 Viewpoint

Context. We present the results of the reverberation monitoring of the MgII broad line and FeII pseudocontinuum for the luminous quasar CTS C30.10 (z = 0.90052) with the Southern African Large Telescope in 2012-2021. Aims. We aimed at disentangling the MgII and UV FeII variability and the first measurement of UV FeII time delay for a distant quasar. Methods. We used several methods for the time-delay measurements and determined the FeII and MgII time delays. We also performed a wavelength-resolved time delay study for a combination of MgII and FeII in the 2700 - 2900 Å rest-frame wavelength range. Results. We obtain a time delay for MgII of 275 . 5 + 12 . 4 − 19 . 5 days in the rest frame, and we have two possible solutions of 270 . 0 + 13 . 8 − 25 . 3 days and 180 . 3 + 26 . 6 − 30 . 0 in the rest frame for FeII. Combining this result with the old measurement of FeII UV time delay for NGC 5548, we discuss for first time the radius-luminosity relation for UV FeII with the slope consistent with 0 . 5 within the uncertainties. Conclusions. Because the FeII time delay has a shorter time-delay component but the lines are narrower than MgII, we propose that the line-delay measurement is biased toward the part of the broad line region (BLR) facing the observer. The bulk of the Fe II emission may arise from the more distant BLR region, however, the region that is shielded from the observer. disks – quasars: emission lines – quasars: individual: CTS C30.10 – Techniques: spectroscopic, photometric

https://www.aanda.org/articles/aa/pdf/forth/aa43194-22.pdf

Wavelength-resolved reverberation mapping of quasar CTS C30.10: Dissecting MgII and FeII emission regions

Anomalous broad-line region responses to continuum variability in active galactic nuclei - I. Hβ variability

In the standard AGN reverberation-mapping model variations in broad-line region (BLR) fluxes are predicted from optical continuum variability (taken as a proxy for variations in the ionizing continuum) convolved with an impulse function that depends on the geometry of the emitting and reprocessing regions. However, it has long been known that BLR variability can deviate from these predictions. We analyze extensive long-term H$\beta$ and continuum monitoring of NGC 5548 and a large sample of high-quality H$\beta$ light curves of other AGNs to investigate the frequency and characteristics of anomalous responses of the BLR. Anomalies are very common and probably occur in every object. Onsets can be on a timescale only slightly longer than the light-crossing time and durations are of the order of the characteristic timescale of variability of the optical continuum to several times longer. Anomalies are larger when NGC 5548 is in a low state, but otherwise there is no correlation with continuum variability. There is abundant evidence for the optical continuum of AGNs varying independently of the higher-energy continua and this is sufficient to explain the anomalous responses. There are good reasons for believing that the frequent lack of correlation between different spectral regions is due to anisotropic and non-axisymmetric emission. Rapid changes in line profiles and velocity-dependent lags are consistent with this. Motion of compact absorbing clouds across the line of sight is another possible cause of anomalies. The prevalence of anomalies needs to be taken into account when planning reverberation-mapping campaigns.

Julia N. Deffner

Papers

Anomalous broad-line region responses to continuum variability in active galactic nuclei - I. Hβ variability

Anomalous Broad-Line Region Responses to Continuum Variability in Active Galactic Nuclei