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NGC 5548 was recently monitored intensively from NIR to X-rays as part of the STORM campaign. Its disc emission was found to lag behind the observed X-rays, while the measured time lag was increasing with wavelength. These results are consistent with the assumption that short-term variability in AGN emission is driven by the X-ray illumination of the accretion disc. In this work, we studied the power spectrum of UV/optical and X-ray emission of NGC 5548, using the data of the STORM campaign as well as previous Swift data, in order to investigate the relation between the UV/optical and X-ray variability and to examine its consistency with the above picture. We demonstrate that even the power spectrum results are compatible with a standard disc being illuminated by X-rays, with low accretion rates, but the details are not entirely consistent with the results from the modelling of the 'τ versus λ' relation. The differences indicate that the inner disc might be covered by a 'warm corona' which does not allow the detection of UV/optical emission from the inner disc. Finally, we found strong evidence that the UV emission of NGC 5548 is not stationary. [ABSTRACT FROM AUTHOR]

Context. The hard X-ray emission of active galactic nuclei (AGN), and in particular, the reflection component, is shaped by the innermost and outer regions of the galactic nucleus. Aims. Our main goal is to investigate the variation of the Compton hump amongst a population of sources and correlate it with other spectral properties to constrain the source geometry. Methods. We studied the NuSTAR hard X-ray spectra of a sample of 83 AGN and performed a detailed spectral analysis of each of them. Based on their spectral shape, we divided the sample into five categories and also studied their stacked spectra. Results. We found a stronger reflection in mildly obscured sources, which verifies the results reported in previous works. In addition, the reflection behaviour, and probably origin, varies with absorption. The accretion disc seems to be the main reflector in unabsorbed sources. A clumpy torus seems to produce most of the reflection in obscured sources. The filling factor of the clouds surrounding the active nucleus is a key parameter that drives the appearance of AGN. Finally, we found that the Fe line and the Compton hump are roughly correlated, as expected. [ABSTRACT FROM AUTHOR]