Context. Active galactic nuclei (AGN) emit radiation over a wide range of wavelengths, with a peak of emission in the far-UV region of the electromagnetic spectrum, a spectral region that is historically difficult to observe. Aims. Using optical, GALEX UV, and XMM-Newton data we derive the spectral energy distribution (SED) from the optical/UV to X-ray regime of a sizeable sample of AGN. The principal motivation is to investigate the relationship between the optical/UV emission and the X-ray emission and provide bolometric corrections to the hard X-ray (2-10 keV) energy range, k bol , the latter being a fundamental parameter in current physical cosmology. Methods. We construct and study the X-ray to optical SED of a sample of 195 X-ray selected Type 1 AGN belonging to the XMM-Newton bright serendipitous survey (XBS). The optical-UV luminosity was computed using data from the Sloan Digital Sky Survey (SDSS), from our own dedicated optical spectroscopy and the satellite GALaxy evolution EXplorer (GALEX), while the X-ray luminosity was computed using XMM-Newton data. Because it covers a wide range of redshift (0.03 < z < ∼ 2.2), X-ray luminosities (41.8 < log L [2−10] keV < 45.5 erg/s) and because it is composed of "bright objects", this sample is ideal for this kind of investigation. Results. We confirm a highly significant correlation between the accretion disc luminosity L disc and the hard X-ray luminosity, where β = 1.18 ± 0.05. We find a very shallow dependence of k bol on the X-ray luminosity with respect to the broad distribution of values of k bol . We find a correlation between k bol and the hard X-ray photon index Γ 2−10 keV and a tight correlation between the optical-to-X-ray spectral index α ox and k bol , so we conclude that both Γ 2−10 keV and α ox can be used as a proxy for k bol .

We study the link between the X-ray emission in radio-quiet active galactic nuclei (AGN) and the accretion rate on the central supermassive black hole using a statistically well-defined and representative sample of 71 type 1 AGN extracted from the XMM-Newton Bright Serendipitous Survey. We search and quantify the statistical correlations between some fundamental parameters that characterize the X-ray emission, i.e. the X-ray spectral slope, , and the X-ray 'loudness', and the accretion rate, both absolute ( Ṁ) and normalized to the Eddington luminosity (Eddington ratio, λ). We parametrize the X-ray loudness using three different quantities: the bolometric correction K bol , the two-point spectral index α OX and the disc/corona luminosity ratio. We find that the X-ray spectral index depends on the normalized accretion rate while the 'X-ray loudness' depends on both the normalized and the absolute accretion rate. The dependence on the Eddington ratio, in particular, is probably induced by the -λ correlation. The two proxies usually adopted in the literature to quantify the X-ray loudness of an AGN, i.e. K bol and α OX , behave differently, with K bol being more sensitive to the Eddington ratio and α OX having a stronger dependence with the absolute accretion. The explanation of this result is likely related to the different sensitivity of the two parameters to the X-ray spectral index.

We present a detailed analysis of the X‐ray spectrum of the Seyfert 2 galaxy NGC 454E, belonging to the interacting system NGC 454. Observations performed with Suzaku, XMM–Newton and Swift allowed us to detect a dramatic change in the curvature of the 2–10 keV spectrum, revealing a significant variation of the absorbing column density along the line of sight (from ∼ 1 × 1024 cm−2 to ∼ 1 × 1023 cm−2). Consequently, we propose this source as a new member of the class of ‘changing look’ active galactic nuclei (AGN), i.e. AGN that have been observed both in Compton thin (NH= 1023  cm−2) and reflection‐dominated states (Compton thick, NH > 1024  cm−2). Due to the quite long time lag (six months) between the Suzaku and XMM–Newton observations, we cannot infer the possible location of the obscuring material causing the observed variability. In the 6–7 keV range, the XMM–Newton observation also shows a clear signature of the presence of an ionized absorber. Since this feature is not detected during the Suzaku observation (despite its detectability), the simplest interpretation is that the ionized absorber is also variable; its location is estimated to be within ∼ 10−3 pc from the central black hole, probably much closer in than the rather neutral absorber.

Aims. We derive masses of the central supermassive black hole (SMBH) and accretion rates for 154 type 1 AGN belonging to a well-defined X-ray-selected sample, the XMM-Newton serendipitous sample (XBS). Methods. We used the most recent "single-epoch" relations, based on Hβ and MgIIλ2798 Å emission lines, to derive the SMBH masses. We then used the bolometric luminosities, computed on the basis of an SED-fitting procedure, to calculate the accretion rates, both absolute and normalized to the Eddington luminosity (Eddington ratio). Results. The selected AGNs cover a range of masses from 10 7 to 10 10 M with a peak around 8 × 10 8 M and a range of accretion rates from 0.01 to ∼50 M /year (assuming an efficiency of 0.1), with a peak at ∼1 M /year. The values of Eddington ratio range from 0.001 to ∼0.5 and peak at 0.1.

We present the results of the analysis of the X-ray spectrum of the Seyfert 2 Mrk 348, observed by Suzaku and XMM-Newton. The overall spectrum of Mrk 348 can be described by a primary power law continuum seen through three layers of absorption, of which one is neutral and two are ionised. Comparing Suzaku (2008) and XMM-Newton (2002) observations we find variability of the X-ray spectral curvature. We suggest that the variability can be explained through the change of column density of both the neutral and one of the ionised absorbers, together with a variation of the ionisation level of the same absorber. We thus confirm one of the main features presented in past works, where intrinsic column density variability up to ∼ 10 23 cm −2 was observed on time scales of months. We also find that the photon index of the underlying power law continuum (Γ ∼ 1.8) is in agreement with the previous observations of this Seyfert 2.