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XMM‐Newton, a European Space Agency observatory, has been observing the X‐ray, ultra‐violet, and optical sky for 23 years. During this time, astronomy has evolved from mainly studying single sources to populations and from a single wavelength, to multi‐wavelength/messenger data. We are also moving into an era of time domain astronomy. New software and methods are required to accompany evolving astronomy and prepare for the next‐generation X‐ray observatory, Athena. Here we present XMM2ATHENA, a program funded by the European Union's Horizon 2020 research and innovation program. XMM2ATHENA builds on foundations laid by the XMM‐Newton Survey Science Centre (XMM‐SSC), including key members of this consortium and the Athena Science ground segment, along with members of the X‐ray community. The project is developing and testing new methods and software to allow the community to follow the X‐ray transient sky in quasi‐real time, identify multi‐wavelength/messenger counterparts of XMM‐Newton sources and determine their nature using machine learning. We detail here the first milestone delivery of the project, a new online, sensitivity estimator. We also outline other products, including the forthcoming innovative stacking procedure and detection algorithms, to detect the faintest sources. These tools will then be adapted for Athena and the newly detected/identified sources will enhance preparation for observing the Athena X‐ray sky. [ABSTRACT FROM AUTHOR]

A complete census of active galactic nuclei (AGNs) is a prerequisite for understanding the growth of supermassive black holes across cosmic time. A significant challenge towards this goal is the whereabouts of heavily obscured AGN that remain uncertain. This paper sets new constraints on the demographics of this population by developing a methodology that combines X-ray spectral information with priors derived from multiwavelength observations. We select X-ray AGN in the Chandra COSMOS Legacy survey and fit their |$2.2\!-\!500\, \mu \mathrm{m}$| spectral energy distributions with galaxy and AGN templates to determine the mid-infrared (⁠|$6\, \mu \mathrm{m}$|⁠) luminosity of the AGN component. Empirical correlations between X-ray and |$6\, \mu \mathrm{m}$| luminosities are then adopted to infer the intrinsic accretion luminosity at X-rays for individual AGN. This is used as prior information in our Bayesian X-ray spectral analysis to estimate physical properties, such as line-of-sight obscuration. Our approach breaks the degeneracies between accretion luminosity and obscuration that affect X-ray spectral analysis, particularly for the most heavily obscured (Compton-Thick) AGN with low photon counts X-ray spectra. The X-ray spectral results are then combined with the selection function of the Chandra COSMOS Legacy survey to derive the AGN space density and a Compton-Thick fraction of |$21.0^{+16.1}_{-9.9}{{\ \rm per\ cent}}$| at redshifts z < 0.5. At higher redshift, our analysis suggests upper limits to the Compton-Thick AGN fraction of |$\lesssim 40{{\ \rm per\ cent}}$|⁠. These estimates are at the low end of the range of values determined in the literature and underline the importance of multiwavelength approaches for tackling the challenge of heavily obscured AGN demographics. [ABSTRACT FROM AUTHOR]

In this paper we explore the scientific synergies between Athena and some of the key multi-messenger facilities that should be operative concurrently with Athena. These facilities include LIGO A+, Advanced Virgo+ and future detectors for ground-based observation of gravitational waves (GW), LISA for space-based observations of GW, IceCube and KM3NeT for neutrino observations, and CTA for very high energy observations. These science themes encompass pressing issues in astrophysics, cosmology and fundamental physics such as: the central engine and jet physics in compact binary mergers, accretion processes and jet physics in Super-Massive Binary Black Holes (SMBBHs) and in compact stellar binaries, the equation of state of neutron stars, cosmic accelerators and the origin of Cosmic Rays (CRs), the origin of intermediate and high-Z elements in the Universe, the Cosmic distance scale and tests of General Relativity and the Standard Model. Observational strategies for implementing the identified science topics are also discussed. A significant part of the sources targeted by multi-messenger facilities is of transient nature. We have thus also discussed the synergy of Athena with wide-field high-energy facilities, taking THESEUS as a case study for transient discovery. This discussion covers all the Athena science goals that rely on follow-up observations of high-energy transients identified by external observatories, and includes also topics that are not based on multi-messenger observations, such as the search for missing baryons or the observation of early star populations and metal enrichment at the cosmic dawn with Gamma-Ray Bursts (GRBs). [ABSTRACT FROM AUTHOR]

We present a statistical analysis of the optical properties of an X-ray-selected Type 1 active galactic nucleus (AGN) sample, using high signal-to-noise ratio (S/N>20) spectra of the counterparts of the ROSAT /2RXS sources in the footprint of the SDSS-IV/SPIDERS (Spectroscopic IDentification of eROSITA Sources) programme. The final sample contains 2100 sources. It significantly extends the redshift and luminosity ranges (z  ∼ 0.01–0.80 and |$L_{\rm 0.1\!-\!2.4 \, keV} \sim \rm 2.0 \times 10^{41}\!-\!1.0 \times 10^{46} \, \, erg \, s^{-1}$|⁠) used so far in this kind of analysis. By means of a principal component analysis, we derive eigenvector (EV) 1 and 2 in an eleven-dimensional optical and X-ray parameter space, which are consistent with previous results. The validity of the correlations of the Eddington ratio L/L Edd with EV1 and the black hole mass with EV2 is strongly confirmed. These results imply that L/L Edd and black hole mass are related to the diversity of the optical properties of Type 1 AGNs. Investigating the relation of the width and asymmetry of H  β and the relative strength of the iron emission |$r_{\rm Fe\, \small{II}}$|⁠ , we show that our analysis supports the presence of a distinct kinematic region: the very broad line region. Furthermore, comparing sources with a red-asymmetric broad H  β emission line to sources for which it is blue asymmetric, we find an intriguing difference in the correlation of the |$\rm Fe\, \small{II}$| and the continuum emission strengths. We show that this contrasting behaviour is consistent with a flattened, stratified model of the broad-line region, in which the |$\rm Fe\, \small{II}$| -emitting region is shielded from the central source. [ABSTRACT FROM AUTHOR]

NGC 3147 has been considered the best case of a true type 2 AGN: an unobscured AGN, based on the unabsorbed compact X-ray continuum, which lacks a broad-line region (BLR). However, the very low luminosity of NGC 3147 implies a compact BLR, which produces very broad lines, hard to detect against the dominant background host galaxy. Narrow (0.1 arcsec × 0.1 arcsec) slit HST spectroscopy allowed us to exclude most of the host galaxy light, and revealed an H  α line with an extremely broad base (FWZI |${\sim }27\, 000$| km s−1). The line profile shows a steep cut-off blue wing and an extended red wing, which match the signature of a mildly relativistic thin accretion disc line profile. It is indeed well fit with a nearly face on thin disc, at i ∼ 23°, with an inner radius at 77 ± 15 r g, which matches the prediction of |$62^{+18}_{-14}$| r g from the R BLR– L 1/2 relation. This result questions the very existence of true type 2 AGN. Moreover, the detection of a thin disc, which extends below 100 r g in an L / L Edd ∼ 10−4 system, contradicts the current view of the accretion flow configuration at extremely low accretion rates. [ABSTRACT FROM AUTHOR]

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We present the first NuSTAR observation of a 'true' type 2 Seyfert galaxy. The 3-40 keV X-ray spectrum of NGC 3147 is characterized by a simple power-law, with a standard Γ ~ 1.7 and an iron emission line, with no need for any further component up to ~40 keV. These spectral properties, together with significant variability on time-scales as short as weeks (as shown in a 2014 Swift monitoring campaign), strongly support an unobscured line of sight for this source. An alternative scenario in terms of a Compton-thick source is strongly disfavoured, requiring an exceptional geometrical configuration, whereas a large fraction of the solid angle to the source is filled by a highly ionized gas, whose reprocessed emission would dominate the observed luminosity. Moreover, in this scenario, the implied intrinsic X-ray luminosity of the source would be much larger than the value predicted by other luminosity proxies, like the [O III]λ5007 emission-line extinction-corrected luminosity. Therefore, we confirm with high confidence that NGC 3147 is a true type 2 Seyfert galaxy, intrinsically characterized by the absence of a broad-line region. [ABSTRACT FROM AUTHOR]

In this paper, the dependence of the broad Fe Kα line on the physical parameters of AGN, such as the black hole mass MBH, accretion rate (equivalently represented by Eddington ratio λEdd) and optical classification is investigated by applying the X-ray spectra stacking method to a large sample of AGN which have well measured optical parameters. A broad-line feature is detected (>3σ) in the stacked spectra of the high λEdd sub-sample (log λEdd > −0.9). The profile of the broad line can be well fitted with relativistic broad-line model, with the line energy consistent with highly ionized Fe Kα line (i.e. Fe xxvi). A model consisting of multiple narrow lines cannot be ruled out, however. We found hints that the Fe K line becomes broader as the λEdd increases. No broad-line feature is shown in the sub-sample of broad-line Seyfert 1 (BLS1) galaxies and in the full sample, while a broad line might be present, though at low significance, in the sub-sample of narrow-line Seyfert 1 (NLS1) galaxies. We find no strong dependence of the broad line on black hole masses. Our results indicate that the detection/properties of the broad Fe Kα line may strongly depend on λEdd, which can be explained if the ionization state and/or truncation radius of the accretion disc changes with λEdd. The non-detection of the broad line in the BLS1 sub-sample can be explained if the average equivalent width of the relativistic Fe Kα line is weak or/and the fraction of sources with relativistic Fe Kα line is small in BLS1 galaxies. [ABSTRACT FROM AUTHOR]

ABSTRACT We present the results of a campaign of simultaneous X-ray and optical observations of 'true' type 2 Seyfert galaxies candidates, i.e. active galactic nuclei without a broad-line region (BLR). Out of the initial sample composed of eight sources, one object, IC 1631, was found to be a misclassified starburst galaxy, another, Q2130−431, does show broad optical lines, while other two, IRAS 01428−0404 and NGC 4698, are very likely absorbed by Compton-thick gas along the line of sight. Therefore, these four sources are not unabsorbed Seyfert 2s as previously suggested in the literature. On the other hand, we confirm that NGC 3147, NGC 3660 and Q2131−427 belong to the class of true type 2 Seyfert galaxies, since they do not show any evidence for a broad component of the optical lines nor for obscuration in their X-ray spectra. These three sources have low accretion rates ( [ABSTRACT FROM AUTHOR]