Swift monitoring of NGC 4151 with an∼6hr sampling over a total of 69 days in early 2016 is used to construct light curves covering five bands in the X-rays (0.3-50keV) and six in the ultraviolet (UV)/optical (1900-5500Å). The three hardest X-ray bands (>2.5keV) are all strongly correlated with no measurable interband lag,while the two softer bands show lower variability and weaker correlations. The UV/optical bands are significantly correlated with the X-rays, lagging ∼3-4days behind the hard X-rays. The variability within the UV/optical bands is also strongly correlated, with the UV appearing to lead the optical by ∼0.5-1days. This combination of 3day lags between the X-rays and UV and 1day lags within the UV/optical appears to rule out the "lamp-post" reprocessing model in which a hot, X-ray emitting corona directly illuminates the accretion disk, which then reprocesses the energy in the UV/optical. Instead, these results appear consistent with the Gardner & Done picture in which two separate reprocessings occur: first, emission from the corona illuminates an extreme-UV-emitting toroidal component that shields the disk from the corona; this then heats the extreme-UV component,which illuminates the disk and drives its variability.

The new multi-wavelength monitoring campaign on NGC 5548 shows clearly that the variability of the UV/optical lightcurves lags by progressively longer times at longer wavelengths, as expected from reprocessing of an optically thick disk, but that the timescales are longer than expected for a standard Shakura-Sunyaev accretion disc. We build a full spectraltiming reprocessing model to simulate the UV/optical lightcurves of NGC 5548. We show that disc reprocessing of the observed hard X-ray lightcurve produces optical lightcurves with too much fast variability as well as too short a lag time. Supressing the fast variability requires an intervening structure preventing the hard X-rays from illuminating the disc. We propose this is the disc itself, perhaps due to atomic processes in the UV lifting the photosphere, increasing the scale-height, making it less dense and less able to thermalise, so that it radiates low temperature Comptonised emission as required to produce the soft X-ray excess. The outer edge of the puffed-up Comptonised disc region emits FUV flux, and can illuminate the outer thin blackbody disc but while this gives reprocessed variable emission which is much closer to the observed UV and optical lightcurves, the light travel lags are still too short to match the data. We reverse engineer a solution to match the observations and find that the luminosity and temperature of the lagged emission is not consistent with material at the light travel lag distance responding to the irradiating flux (either FUV or X-ray) from the AGN. We conclude that the UV/optical lags of NGC 5548 are not the light travel time from X-ray reprocessing, nor the light travel time from FUV reprocessing, but instead could be the timescale for the outer blackbody disc vertical structure to respond to the changing FUV illumination.

We model the ultraviolet spectra of the Seyfert 1 galaxy NGC 5548 obtained with the Hubble Space Telescope during the 6 month reverberation mapping campaign in 2014. Our model of the emission from NGC 5548 corrects for overlying absorption and deblends the individual emission lines. Using the modeled spectra, we measure the response to continuum variations for the deblended and absorption-corrected individual broad emission lines, the velocity-dependent profiles of Lyα and C iv, and the narrow and broad intrinsic absorption features. We find that the time lags for the corrected emission lines are comparable to those for the original data. The velocity-binned lag profiles of Lyα and C iv have a double-peaked structure indicative of a truncated Keplerian disk. The narrow absorption lines show a delayed response to continuum variations corresponding to recombination in gas with a density of ∼105 cm−3. The high-ionization narrow absorption lines decorrelate from continuum variations during the same period as the broad emission lines. Analyzing the response of these absorption lines during this period shows that the ionizing flux is diminished in strength relative to the far-ultraviolet continuum. The broad absorption lines associated with the X-ray obscurer decrease in strength during this same time interval. The appearance of X-ray obscuration in ∼2012 corresponds with an increase in the luminosity of NGC 5548 following an extended low state. We suggest that the obscurer is a disk wind triggered by the brightening of NGC 5548 following the decrease in size of the broad-line region during the preceding low-luminosity state.

The detection of several radio-loud narrow-line Seyfert 1 (NLS1) galaxies by the Fermi Gamma-Ray Space Telescope hints at the existence of a rare, new class of γ-ray emitting active galactic nuclei with low black hole masses. Like flat spectrum radio quasars (FSRQs), their γ-ray emission is thought to be produced via the external Compton mechanism whereby relativistic jet electrons upscatter a photon field external to the jet, e.g. from the accretion disc, broad line region (BLR) and dusty torus, to higher energies. Here we study the origin of the γ-ray emission in the lowest-redshift candidate among the currently-known γ-ray emitting NLS1s, 1H 0323+342, and take a new approach. We observationally constrain the external photon field using quasisimultaneous near-IR, optical and X-ray spectroscopy. Applying a one-zone leptonic jet model, we simulate the range of jet parameters for which this photon field, when Compton scattered to higher energies, can explain the γ-ray emission. We find that the site of the γ-ray emission lies well within the BLR and that the seed photons mainly originate from the accretion disc. The jet power that we determine, 1.0 × 10 45 erg s −1 , is approximately half the accretion disc luminosity. We show that this object is not simply a low-mass FSRQ, its jet is intrinsically less powerful than predicted by scaling a typical FSRQ jet by black hole mass and accretion rate. That γ-ray emitting NLS1s appear to host underpowered jets may go some way to explaining why so few have been detected to date.

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