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The ASTRI Mini-Array is a next-generation system of nine imaging atmospheric Cherenkov telescopes that is going to be built at the Observatorio del Teidesite. After a first phase, in which the instrument will be operated as an experiment prioritizing a schedule of primary science cases, an observatory phase is foreseen in which other significant targets will be pointed. We focus on the observational feasibility of extragalactic sources and on astrophysical processes that best complement and expand the ASTRI Mini-Array core science, presenting the most relevant examples that are at reach of detection over long-term time scales and whose observation can provide breakthrough achievements in the very-high energy extragalactic science. Such examples cover a wide range of γ-ray emitters, including the study of AGN low states in the multi-TeV energy range, the possible detection of Seyfert galaxies with long exposures and the searches of dark matter lines above 10 TeV. Simulations of the presented objects show that the instrument performance will be competitive at multi-TeV energies with respect to current arrays of Cherenkov telescopes.

The ASTRI (Astrofisica con Specchi a Tecnologia Replicante Italiana) Project led by the Italian National Institute for Astrophysics (INAF) is developing and will deploy at the Observatorio del Teidea mini-array (ASTRI Mini-Array) composed of nine telescopes similar to the small-size dual-mirror Schwarzschild-Couder telescope (ASTRI-Horn) currently operating on the slopes of Mt. Etna in Sicily. The ASTRI Mini-Array will surpass the current Cherenkov telescope array differential sensitivity above a few tera-electronvolt (TeV), extending the energy band well above hundreds of TeV. This will allow us to explore a new window of the electromagnetic spectrum, by convolving the sensitivity performance with excellent angular and energy resolution figures. In this paper we describe the Core Science that we will address during the first four years of operation, providing examples of the breakthrough results that we will obtain when dealing with current open questions, such as the acceleration of cosmic rays, cosmology and fundamental physics and the new window, for the TeV energy band, of the time-domain astrophysics.

We discuss a long Suzaku observation of IRAS 19254-7245 (also known as the Superantennae), one of the brightest and well studied Ultra Luminous Infrared Galaxies in the local Universe. This long observation provided the first detection of IRAS 19254-7245 above 10 keV, and a measurement of a 15–30 keV flux of ~$5\times 10^{-12}$erg cm-2s-1. The detection above 10 keV has allowed us to determine, for the first time, the intrinsic luminosity of the AGN hosted in IRAS 19254-7245, which is strongly absorbed ($N_\mathrm{H}\sim 3\times10^{24}$cm-2) and has an intrinsic luminosity ($L(2-10$keV) ~$3\times 10^{44}$erg s-1) in the QSO regime. The 2–10 keV spectrum of IRAS 19254-7245 is remarkably hard ($\Gamma\sim 1.2$), and presents a strong iron line ($EW \sim 0.7$keV), clearly suggesting that below 10 keV we observe only reprocessed radiation. Since the energy of the Fe K emission is found to be ~6.7 keV, consistent with He-like Fe, and its EW is too high to be explained by a starburst-dominated scenario, we suggest that the 2–10 keV emission of IRAS 19254-7245 is dominated by reflection/scattering from highly ionized matter. Within this latter scenario, we found that the photon index of the illuminating source is $\Gamma=1.87^{+0.11}_{-0.28}$, in excellent agreement with the mean value found for radio quiet unobscured AGN.

Aims. Pointed observations with XMM-Newton provide the basis for creating catalogues of X-ray sources detected serendipitously in each field. This paper describes the creation and characteristics of the 2XMM catalogue.

Aims. To study the cosmological evolution of active galactic nuclei (AGN) is one of the main goals of X-ray surveys. To accurately determine the intrinsic (before absorption) X-ray luminosity function, it is essential to constrain the evolutionary properties of AGN and therefore the history of the formation of supermassive black holes with cosmic time.

Aims. We investigate here the X-ray luminosity function (XLF) of absorbed (NHbetween 4 $\times$1021and 1024cm-2) and unabsorbed (NH< 4 $\times$1021cm-2) AGN, the fraction of absorbed AGN as a function of LX(and z), the intrinsic NHdistribution of the AGN population, and the XLF of Compton thick (NH> 1024cm-2) AGN.

Aims.We present the optical classification and redshift of 348 X-ray selected sources from the XMM-NewtonBright Serendipitous Survey (XBS), which contains a total of 400 objects (identification level = 87%). About 240 are new identifications. In particular, we discuss in detail the classification criteria adopted for the active galactic nuclei (AGNs) population.

Aims.X-ray sources at intermediate fluxes (a few $\times$10-14erg cm-2s-1) with a sky density of ~100 deg-2are responsible for a significant fraction of the cosmic X-ray background at various energies below 10 keV. The aim of this paper is to provide an unbiased and quantitative description of the X-ray source population at these fluxes and in various X-ray energy bands.

Context.Optical follow-up of X-ray selected sources finds a significant fraction of “optically dull” sources characterized by optical spectra without obvious signature of AGN activity. In many cases, however, the presence of an AGN is inferred from other diagnostics (e.g. the X-ray properties). Understanding and accounting for this “elusiveness” is mandatory for a reliable study of the AGN physical and statistical properties.

Context.Recent results have revised upwards the total X-ray background (XRB) intensity below ~10 keV, therefore an accurate determination of the source counts is needed. There are also contradictory results on the clustering of X-ray selected sources.

Aims.We aim to test a method of efficiently selecting X-ray obscured AGN in the 2XMM-NewtonEPIC Serendipitous Source Catalogue.

Context.The comparison of observed counts in a given sky direction with predictions by Galactic models yields constraints on the spatial distribution and the stellar birthrate of young stellar populations. The XMM-Newton Bright Serendipitous Survey (XBSS) is an unbiased survey that includes a total of 58 stellar sources selected in the 0.5–4.5 keV energy band, having a limiting sensitivity of 10-2cnt s-1and covering an area of 28.10 sq deg.

We present the XMM-Newton and the optical-VLT spectra along with the optical and the near-infrared photometric data of one of the brightest X-ray ($F_{2{-}10~\rm keV}\sim10^{-13}$erg s-1cm-2) extremely red objects ($R-K\ge5$) discovered so far. The source, XBS J0216-0435, belongs to the XMM-Newton Bright Serendipitous Surveyand it has extreme X-ray-to-optical (~220) and X-ray-to-near-infrared (~60) flux ratios. Thanks to its brightness, the X-ray statistics are good enough for an accurate spectral analysis by which the presence of an X-ray obscured ($N_{\rm H}>10^{22}$cm-2) QSO ($L_{2{-}10~\rm keV}=4\times10^{45}$erg s-1) is determined. A statistically significant (~99%) excess around 2 keV in the observed-frame suggests the presence of an emission line. By assuming that this feature corresponds to the iron Kαline at 6.4 keV, a first estimate of the redshift of the source is derived ($z_{\rm X}\sim2$). The presence of a high redshift QSO2 has been finally confirmed through dedicated VLT optical spectroscopic observations ($z_{\rm O}=1.985\pm0.002$). This result yields to an optical validation of a new X-ray Line Emitting Object (XLEO) for which the redshift has been firstly derived from the X-ray data. XBS J0216-0435 can be considered one of the few examples of X-ray obscured QSO2 at high redshift for which a detailed X-ray and optical spectral analysis has been possible. The spectral energy distribution from radio to X-rays is also presented. Finally from the near-infrared data the luminosity and the stellar mass of the host galaxy has been estimated finding a new example of the coexistence at high-zbetween massive galaxies and powerful QSOs.

Results obtained from an X-ray spectral survey of nearby Seyfert galaxies using XMM–Newtonare reported. The sample was optically selected, well defined, complete in Bmagnitude, and distance limited: it consists of the nearest ($D \la22$Mpc) 27 Seyfert galaxies (9 of type 1, 18 of type 2) taken from the Ho et al. (1997a, ApJS, 112, 315) sample. This is one of the largest atlases of hard X-ray spectra of low-luminosity active galaxies ever assembled. All nuclear sources except two Seyfert 2s are detected between 2 and 10 keV, half for the first time ever, and average spectra are obtained for all of them. Nuclear luminosities reach values down to 1038erg s-1. The shape of the distribution of X-ray parameters is affected by the presence of Compton-thick objects ($\ga$30% among type 2s). The latter have been identified either directly from their intense FeK line and flat X-ray spectra, or indirectly with flux diagnostic diagrams which use isotropic indicators. After taking into account these highly absorbed sources, we find that (i) the intrinsic X-ray spectral properties (i.e., spectral shapes and luminosities above 2 keV) are consistent between type 1 and type 2 Seyferts, as expected from “unified models”; (ii) Seyfert galaxies as a whole are distributed fairly continuously over the entire range of NH, between 1020and 1025cm-2; and (iii) while Seyfert 1s tend to have lower NHand Seyfert 2s tend to have the highest, we find 30% and 10% exceptions, respectively. Overall the sample is of sufficient quality to well represent the average intrinsic X-ray spectral properties of nearby active galactic nuclei, including a proper estimate of the distribution of their absorbing columns. Finally, we conclude that, with the exception of a few cases, the present study agrees with predictions of unified models of Seyfert galaxies, and extends their validity down to very low luminosities.

This paper presents the X-ray spectroscopy of an X-ray selected sample of 25 radio-loud (RL) AGNs extracted from the XMM-NewtonBright Serendipitous Survey (XBSS). The main goal of the work is to assess and study the origin of the X-ray spectral differences usually observed between radio-loud and radio-quiet (RQ) AGNs. To this end, a comparison sample of 53 RQ AGNs has been also extracted from the same XBSS sample and studied together with the sample of RL AGNs. Since there are many claims in the literature that RL AGNs have, on average, a flatter spectral index when compared to the RQ AGNs, we have focused the analysis on the distribution of the X-ray spectral indices of the power-law component that models the large majority of the spectra in both samples. We find that the mean X-ray energy spectral index is very similar in the 2 samples and close to $\alpha_{\rm X}\sim1$. However, the intrinsic distribution of the spectral indices is significantly broader in the sample of RL AGNs. In order to investigate the origin of this difference, we have divided the RL AGNs into blazars (i.e. BL Lac objects and FSRQs) and “non-blazars” (i.e. radiogalaxies and SSRQs), on the basis of the available optical and radio information. Although the number of sources is small, we find strong evidence that the broad distribution observed in the RL AGN sample is mainly due to the presence of the blazars. Furthermore, within the blazar class we have found a link between the X-ray spectral index and the value of the radio-to-X-ray spectral index ($\alpha_{\rm RX}$) suggesting that the observed X-ray emission is directly connected to the emission of the relativistic jet. This trend is not observed among the “non-blazars” RL AGNs. This favours the hypothesis that, in these latter sources, the X-ray emission is not significantly influenced by the jet emission and it has probably an origin similar to the RQ AGNs. Overall, the results presented here indicate that the observed distribution of the X-ray spectral indices in a given sample of RL AGNs is strongly dependent on the amount of relativistic beaming present in the selected sources, i.e. on the relative fraction of blazars and “non-blazars”.

We present here “The XMM-Newton Bright Serendipitous Survey”, composed of two flux-limited samples: the XMM-Newton Bright Source Sample (BSS, hereafter) and the XMM-Newton “Hard” Bright Source Sample (HBSS, hereafter) having a flux limit of $f_x\simeq 7 \times 10^{-14}$erg cm-2s-1in the 0.5-4.5 keV and 4.5-7.5 keV energy band, respectively. After discussing the main goals of this project and the survey strategy, we present the basic data on a complete sample of 400 X-ray sources (389 of them belong to the BSS, 67 to the HBSS with 56 X-ray sources in common) derived from the analysis of 237 suitable XMM-Newton fields (211 for the HBSS). At the flux limit of the survey we cover a survey area of 28.10 (25.17 for the HBSS) sq. deg. The extragalactic number-flux relationships (in the 0.5-4.5 keV and in the 4.5-7.5 keV energy bands) are in good agreement with previous and new results making us confident about the correctness of data selection and analysis. Up to now ${\sim} 71$% (${\sim} 90$%) of the sources have been spectroscopically identified making the BSS (HBSS) the sample with the highest number of identified XMM-Newton sources published so far. At the X-ray flux limits of the sources studied here we found that: a) the optical counterpart in the majority (${\sim} 90$%) of cases has a magnitude brighter than the POSS II limit ($R \sim 21^{\rm mag}$); b) the majority of the objects identified so far are broad line AGN both in the BSS and in the HBSS. No obvious trend of the source spectra (as deduced from the Hardness Ratios analysis) as a function of the count rate is measured and the average spectra of the “extragalactic” population corresponds to a (0.5-4.5 keV) energy spectral index of ${\sim} 0.8$(${\sim} 0.64$) for the BSS (HBSS) sample. Based on the hardness ratios we infer that about 13% (40%) of the sources in the BSS (HBSS) sample are described by an energy spectral index flatter than that of the cosmic X-ray background. Based on previous X-ray spectral results on a small subsample of objects we speculate that all these sources are indeed absorbed AGN with the NHranging from a few times 1021up to few times 1023cm-2. We do not find strong evidence that the 4.5-7.5 keV survey is sampling a completely different source population if compared with the 0.5-4.5 keV survey; rather we find that, as expected from the CXB synthesis models, the hard survey is simply picking up a larger fraction of absorbed AGN. At the flux limit of the HBSS sample we measure surface densities of optically type 1 and type 2 AGN of $1.63\pm 0.25$deg-2and $0.83\pm 0.18$deg-2, respectively; optically type 2 AGN represent $34\pm 9\%$of the total AGN population. Finally, we have found a clear separation, in the hardness ratio diagram and in the (hardness ratio) vs. (X-ray to optical flux ratio) diagram, between Galactic “coronal emitting” stars and extragalactic sources. The information and “calibration” reported in this paper will make the existing and incoming XMM-Newton catalogs a unique resource for astrophysical studies.

The Early Data Release of the Sloan Digital Sky Survey (SDSS) contains 150 Narrow–Line Seyfert 1 (NLS1) galaxies, most of them previously unknown. We present here the study of the X-ray emission from two of these active galaxies (SDSS J030639.57+000343.2 and SDSS J141519.50-003021.6), based upon XMM-Newtonobservations. The spectral and timing characteristics of the two sources are presented and compared to the typical properties of known NLS1 galaxies. We found that these two NLS1 are within the dispersion range of the typical values of this class of AGN, although with some interesting features that deserve further studies.

We report the discovery of a Compton-thick AGN and of intense star-formation activity in the nucleus and disk, respectively, of the nearly edge-on superwind galaxy NGC 4666. Spatially unresolved emission is detected by BeppoSAXonly at energies <10 keV, whereas spatially resolved emission from the whole disk is detected by XMM-Newton. A prominent ($EW \sim 1{-}2$keV) emission line at ~6.4 keV is detected by both instruments. From the XMM-Newtondata alone the line is spectrally localized at $E \simeq 6.42 \pm 0.03$keV, and seems to be spatially concentrated in the nuclear region of NGC 4666. This, together with the presence of a flat ($\Gamma\sim 1.3$) continuum in the nuclear region, suggests the existence of a strongly absorbed (i.e., Compton-thick) AGN, whose intrinsic 2–10 keV luminosity is estimated to be $L_{2{-}10} \ga2 \times 10^{41}$erg s-1. At energies $\la$1 keV the integrated (BeppoSAX) spectrum is dominated by a ~0.25 keV thermal gas component distributed throughout the disk (resolved by XMM-Newton). At energies ~2–10 keV, the integrated spectrum is dominated by a steep ($\Gamma\ga2$) power-law (PL) component. The latter emission is likely due to unresolved sources with luminosity $L \sim 10^{38}{-}10^{39}$erg s-1that are most likely accreting binaries (with BH masses ≤8 $M_\odot$). Such binaries, which are known to dominate the X-ray point-source luminosity in nearby star-forming galaxies, have $\Gamma\sim 2$PL spectra in the relevant energy range. A $\Gamma\sim 1.8$PL contribution from Compton scattering of (the radio-emitting) relativistic electrons by the ambient FIR photons may add a truly diffuse component to the 2–10 keV emission.

We discuss XMM-Newtonand BeppoSAX observations of MKN 231, the lowest-redshift Broad Absorption Line (BAL) QSO known so far and one of the best-studied Ultra Luminous Infrared Galaxies. By combining the XMM-Newtonspectral resolution and the high-energy bandpass of BeppoSAX we have been able to study in more detail than previously possible its 0.2–50 keV spectral properties. The BeppoSAX PDS data unveiled, for the first time, a highly absorbed ($N_{\rm H}\sim 2\times 10^{24}$cm-2) power-law component. We find that: a) below 10 keV we are seeing only reprocessed radiation through reflection and/or scattering; b) the intrinsic 2–10 keV luminosity of MKN 231 is $ 1^{+1.0}_{-0.5} \times 10^{44}$erg s-1, i.e. more than an order of magnitude greater than previous measurements; c) the starburst activity significantly contributes to the soft ($E<2$keV) X-ray emission.

Based on recent work on spectral decomposition of the emission of star-forming galaxies, we assess whether the integrated 2-10 keV emission from high-mass X-ray binaries (HMXBs), $L_{2-10}^{\rm HMXB}$, can be used as a reliable estimator of ongoing star formation rate (SFR). Using a sample of 46 local ($z \la0.1$) star-forming galaxies, and spectral modeling of ASCA, BeppoSAX, and XMM-Newton data, we demonstrate the existence of a linear SFR– $L_{2-10}^ {\rm HMXB}$relation which holds over ~5 decades in X-ray luminosity and SFR. The total 2-10 keV luminosity is nota precise SFRindicator because at low SFR(i.e., in normal and moderately-starbursting galaxies) it is substantially affected by the emission of low-mass X-ray binaries, which do not trace the current SFRdue to their long evolution lifetimes, while at very high SFR(i.e., for very luminous FIR-selected galaxies) it is frequently affected by the presence of strongly obscured AGNs. The availability of purely SB-powered galaxies – whose 2-10 keV emission is mainly due to HMXBs – allows us to properly calibrate the SFR– $L_{2-10}^{\rm HMXB}$relation. The SFR– $L_{2-10}^{\rm HMXB}$relation holds also for distant ($z \sim 1$) galaxies in the HubbleDeep Field North sample, for which we lack spectral information, but whose SFRcan be estimated from deep radio data. If confirmed by more detailed observations, it may be possible to use the deduced relation to identify distant galaxies that are X-ray overluminous for their (independently estimated) SFR, and are therefore likely to hide strongly absorbed AGNs.

XMM-Newtonobservations are presented for the $z=0.83$cluster of galaxies MS 1054-0321, the highest redshift cluster in the EinsteinExtended Medium Sensitivity Survey (EMSS). The temperature inferred by the XMM-Newtondata, $T=7.2^{+0.7}_{-0.6}$keV, is much lower than the temperature previously reported from ASCA data, $T=12.3^{+3.1}_{-2.2}$keV (Donahue et al. 1998), and a little lower than the Chandra temperature, $T=10.4^{+1.7}_{-1.5}$keV, determined by Jeltema et al. 2001. The discrepancy between the newly derived temperature and the previously derived temperatures is discussed in detail. If one allows the column density to be a free parameter, then the best fit temperature becomes $T=8.6^{+1.2}_{-1.1}$keV, and the best fit column density becomes $N_{\rm H}=1.33^{+0.15}_{-0.14}\times10^{20}$atoms cm-2. The iron line is well detected in the XMM-Newtonspectrum with a value for the abundance of $Z=0.33^{+0.19}_{-0.18}~Z_{\odot}$, in very good agreement with previous determinations. The derived XMM X-ray luminosity for the overall cluster in the 2–10 keV energy band is $L_{\rm X}=(3.81\pm0.19) \times10^{44}~h^{-2}$erg s-1while the bolometric luminosity is $L_{\rm BOL}=(8.05\pm0.40) \times10^{44}~h^{-2}$erg s-1. The XMM-Newtondata confirm the substructure in the cluster X-ray morphology already seen by ROSAT and in much more detail by Chandra. We find that only two of the three clumps detected in the weak lensing mass reconstruction image are visible in X-rays, as already noted by [CITE]. The central weak lensing clump is coincident with the main cluster component and has a temperature $T=8.1^{+1.3}_{-1.2}$keV. The western weak lensing clump coincides with the western X-ray component which is much cooler with a temperature $T=5.6^{+0.8}_{-0.6}$keV. The optically measured velocity dispersion, obtained from 145 cluster redshifts, is consistent with the velocity dispersion expected from the $\sigma_{V}-T_{\rm X}$relationship once the XMM-Newtontemperature is used. MS 1054-0321 fits well in the $\sigma \propto T^{1/2}$correlation available in the literature and derived from information collected for all clusters at redshfits of $z\leq1.27$known today and with a measured X-ray temperature. The cluster temperature seems to be commensurate with the predictions from its X-ray luminosity from the $L_{\rm X}-T_{\rm X}$relation of local clusters. Given the newly determined temperature, MS 1054-0321 is no longer amongst the hottest clusters known.

This paper presents the analysis of a statistically complete sample of 28 serendipitous X-ray sources selected in 82 pointed XMM-Newtonfields down to a count-rate of 0.002 counts s-1(4.5–7.5 keV energy band). This is the first sample selected in this energy range to have complete spectroscopic identifications and redshift determinations for all the objects. Apart from one Galactic source (an interacting binary), all the objects are AGNs. Their optical and X-ray properties (derived from the spectral analysis of the XMM-EPIC data) are compared together. The good correlation between the optical spectral type and the X-ray absorption properties supports the AGN unified model. Only one object that does not fit the relation between optical and X-ray absorption is found, namely a Seyfert 1.9 with no evidence of obscuration in the X-ray band ($N_{\rm H}<1.3\times10^{20}$cm-2). In total, 7 sources out of 27 are heavily obscured in the X-ray ($N_{\rm H}>10^{22}$cm-2), corresponding to a surface density of 0.7 deg-2at the flux limit the sample ($4{-}7\times10^{-14}$erg s-1cm-2in the 4.5–7.5 keV energy band). Among these obscured objects, two sources show a large (intrinsic) luminosity ($L_{\rm{[2{-}10~keV]}}>10^{44}$erg s-1) and are thus classified as type 2 QSO. Finally, we have compared the fraction of X-ray absorbed AGNs (26%) with that predicted by the current XRB synthesis models at the flux limit of the survey. We find that the models significantly (~90% confidence level) over predict the fraction of absorbed AGNs thus confirming also in this hard energy band (4.5–7.5 keV) similar results recently obtained in the 2–10 keV band.

We discuss the X-ray, optical and radio properties of AX J0843+2942, a high luminosity Type 2 AGN found in the ASCA Hard Serendipitous Survey. The X-ray spectrum is best described by an absorbed power-law model with a photon index of $\Gamma = 1.72^{+0.3}_{-0.6}$and intrinsic absorbing column density of $N_{\rm H} = 1.44^{+0.33}_{-0.52} \times 10^{23}$cm-2. The intrinsic luminosity in the 0.5-10 keV energy band is $\simeq$$3\times 10^{45}$erg s-1, well within the range of quasar luminosities. AX J0843+2942, positionally coincident with the core of a triple and strong ($S_{\rm 1.4~GHz} \sim 1$Jy; $P_{\rm 1.4~GHz} \sim 9\times 10^{33}$erg s-1Hz-1) radio source, is spectroscopically identified with a Narrow Line object (intrinsic FWHMof all the permitted emission lines $\la$1200 km s-1) at $z=0.398$, having line features and ratios typical of Seyfert-2 like objects. The high X-ray luminosity, coupled with the high intrinsic absorption, the optical spectral properties and the radio power, allow us to propose AX J0843+2942 as a Radio-Loud “Type 2 QSO". A discussion of the SED of this object is presented here together with a comparison with the SED of Ultra Luminous Infrared Galaxies, other “Type 2 QSO" candidates from the literature, and “normal" Radio-Quiet and Radio-Loud QSOs.

We have performed a detailed analysis of 3 optically normal galaxies extracted from the XMM Bright Serendipitous Source Sample. Thanks to the good statistics of the XMM-Newtondata, we have unveiled the presence of an AGN in all of them. In particular, we detect both X-ray obscured ($N_{\rm H}>10^{22}$cm-2) and unobscured ($N_{\rm H}<10^{22}$cm-2) AGNs with intrinsic 2–10 keV luminosities in the range between 1042–1043erg s-1. We find that the X-ray and optical properties of the sources discussed here could be explained assuming a standard AGN hosted by galaxies with magnitudes $M_R< M ^*$, taking properly into account the absorption associated with the AGN, the optical faintness of the nuclear emission with respect to the host galaxy, and the inadequate set-up and atmospheric conditions during the optical spectroscopic observations. Our new spectroscopic observations have revealed the expected AGN features also in the optical band. These results clearly show that optical spectroscopy sometimes can be inefficient in revealing the presence of an AGN, which instead is clearly found from an X-ray spectroscopic investigation. This remarks the importance of being careful in proposing the identification of X-ray sources (especially at faint fluxes) when only low quality optical spectra are in hand. This is particularly important for faint surveys (such as those with XMM-Newtonand Chandra), in which optically dull but X-ray active objects are being found in sizeable numbers.

We present the XMM-Newtonobservation of the merging system IRAS 19254-7245, also known as The Superantennae, whose southern nucleus is classified as a Seyfert 2 galaxy. The XMM-Newtondata have allowed us to perform a detailed X-ray imaging and spectral analysis of this system. We clearly detect, for the first time in this system, a strong ($EW \sim 1.4$keV) Fe emission line at $6.49\pm 0.1$keV (rest-frame). The X-ray spectrum requires a soft thermal component ($kT\sim0.9$keV; $L_{0.5-2}\sim 4\times10^{41}$erg s-1), likely associated with the starburst, and a hard power-law continuum above 2 keV (observed $L_{2-10}\sim 4\times10^{42}$erg s-1). We confirm the flatness of this latter component, already noted in previous ASCA data. This flatness, together with the detection of the strong Fe-Kaline and other broad band indicators, suggest the presence of a Compton-thick AGN with intrinsic luminosity ?1044erg s-1. We show that a Compton-thick model can perfectly reproduce the X-ray spectral properties of this object.

We present the results of TNG near-IR low resolution spectroscopy of two (S7F5_254 and S7F5_45) sources belonging to a complete sample of 15 EROs with K'$<18$and $R-K'$$>5$selected from the MUNICS Survey. Both the spectra show a sharp drop in the continuum which can be ascribed only to the Balmer break. This places them at 1.2 $

We present the results of the X-ray spectral analysis of the first deep X-ray survey with the XMM-Newton observatory during Performance Verification. The X-ray data of the Lockman Hole field and the derived cumulative source counts were reported by Hasinger et al. (2001). We restrict the analysis to the sample of 98 sources with more than 70 net counts (flux limit in the [0.5–7] keV band of $1.6 \times 10^{-15}$erg cm-2s-1) of which 61 have redshift identification. We find no correlation between the spectral index Γand the intrinsic absorption column density NHand, for both the Type-1 and Type-2 AGN populations, we obtain $\langle\Gamma\rangle \simeq 2$. The progressive hardening of the mean X-ray source spectrum with decreasing flux is essentially due to an increase in intrinsic absorption. The marked separation between the two AGN populations in several diagnostics diagrams, involving X-ray colour, X-ray flux, optical/near IR colour and optical brightness, is also a consequence of different absorption column densities and enables the classification of optically faint obscured AGN. The Type-2 and obscured AGN have weaker soft X-ray and optical fluxes and redder $R-K^\prime$colours. They follow the evolutionary tracks of their host galaxies in a color-redshift diagram. About 27% of the subsample with $R-K^\prime$colour are EROs ($R-K^\prime \geq 5$) and most of these 18 X-ray selected EROs contain an obscured AGN as revealed by their high X-ray-to-optical/near IR flux ratios. There are six sources in our sample with $L_{\rm X}[0.5{-}10]>10^{44}$erg s-1and $\log(N_{\rm H})>10^{22}$cm-2: which are likely Type-2 QSOs and we thus derive a density of ∼69 objects of this class per square degree.

We present the first results on the identifications of a medium sensitivity survey (X-ray flux limit $2\times 10^{-14}\, {\rm erg}\, {\rm cm}^{-2}\, {\rm s}^{-1}$in the 0.5–4.5 keV band) at high galactic latitude (${{\mid}b{\mid}}>20^{\circ}$) carried out with the XMM-Newton X-ray observatory within the AXIS observing programme. This study is being conducted as part of the XMM-Newton Survey Science Centre activities towards the identification of the sources in the X-ray serendipitous sky survey. The sample contains 29 X-ray sources in a solid angle of $0.26\deg^2$(source density $113\pm 21$sources $\deg^{-2}$), out of which 27 (93%) have been identified. The majority of the sources are broad-line AGN (19), followed by narrow emission line X-ray emitting galaxies (6, all of which turn out to be AGN), 1 nearby non-emission line galaxy (NGC 4291) and 1 active coronal star. Among the identified sources we find 2 broad-absorption line QSOs ($z\sim 1.8$and $z\sim 1.9$), which constitute ~10% of the AGN population at this flux level, similar to optically selected samples. Identifications of a further 10 X-ray sources fainter than our survey limit are also presented.

We discuss BeppoSAX observations and archive ASCA data of NGC 7679, a nearby, nearly face-on SB0 galaxy in which starburst and AGN activities coexist. The X-ray observations reveal a bright ($L_{0.1-50 \rm keV} \sim 2.9 \times 10^{43}$erg s-1) and variable source having a minimum observed doubling/halving time scale of ~10-20 ksec. A simple power law with photon index of $\Gamma \sim 1.75$and small absorption ($N_{\rm H} < 4\times 10^{20}$cm-2) can reproduce the NGC 7679 spectrum from 0.1 up to 50 keV. These X-ray properties are unambiguous signs of Seyfert 1 activity in the nucleus of NGC 7679. The starburst activity, revealed by the IR emission, optical spectroscopy and Hαimaging, and dominating in the optical and IR bands, is clearly overwhelmed by the AGN in the X-ray band. Although, at first glance, this is similar to what is observed in other starburst-AGN galaxies (e.g. NGC 6240, NGC 4945), most strikingly here and at odds with the above examples, the X-ray spectrum of NGC 7679 does not appear to be highly absorbed. The main peculiarity of objects like NGC 7679 is not the strength of their starburst but the apparent optical weakness of the Seyfert 1 nucleus when compared with its X-ray luminosity. To date NGC 7679 is one of the few Seyfert 1/Starburst composites for which the broad-band X-ray properties have been investigated in detail. The results presented here imply that optical and infrared spectroscopy could be highly inefficient in revealing the presence of an AGN in these kinds of objects, which instead is clearly revealed from X-ray spectroscopic and variability investigations.

We present 71 Emission Line objects selected from the REX survey. Except for 3 of them, for which the presence of an active nucleus is dubious, all these sources are Active Galactic Nuclei (QSOs, Seyfert galaxies, emission line radiogalaxies). In addition, we present the spectra of other 19 AGNs included in a preliminary version of the REX catalog but not in the final one. The majority (80) of the 90 sources presented in this paper is newly discovered. Finally, we present the general properties in the radio and in the X-ray band of all the AGNs discovered so far in the REX survey.

We have observed 28 sources selected from the 1Jy sample of BL Lac objects [(Stickel et al. 1991)] with the Very Large Array (VLA) in A, B and D configurations at 1.36, 1.66 and 4.85 GHz, and/or with the Westerbork Synthesis Radio Telescope (WSRT) at 1.40 GHz. In this paper we present high sensitivity images at arcsecond resolution of the 18 objects showing extended structure in our images, and of another source from the FIRST (Faint Images of the Radio Sky at Twenty-cm) survey [(Becker et al. 1995).] In general our high sensitivity images reveal an amount of extended emission larger than previously reported. In some objects the luminosity of the extended structure is comparable with that of FR II radio sources. A future paper will be devoted to the interpretation of these results.

The ASTRI Mini-Array (MA) is an INAF project to build and operate a facility to study astronomical sources emitting at very high-energy in the TeV spectral band. The ASTRI MA consists of a group of nine innovative Imaging Atmospheric Cherenkov telescopes. The telescopes will be installed at the Teide Astronomical Observatory of the Instituto de Astrofisica de Canarias (IAC) in Tenerife (Canary Islands, Spain) on the basis of a host agreement with INAF. Thanks to its expected overall performance, better than those of current Cherenkov telescopes' arrays for energies above ∼5 TeV and up to 100 TeV and beyond, the ASTRI MA will represent an important instrument to perform deep observations of the Galactic and extra-Galactic sky at these energies.

Context. Our knowledge of the properties of AGN, especially those of optical type-2 objects, is very incomplete. Because extragalactic source count distributions are dependent on the cosmological and statistical properties of AGN, they provide a direct method of investigating the underlying source populations.Aims. We aim to constrain the extragalactic source count distributions over a broad range of X-ray fluxes and in various energy bands to test whether the predictions from X-ray background synthesis models agree with the observational constraints provided by our measurements.Methods. We have used 1129 XMM-Newton observations at |b|>20?covering a total sky area of 132.3?deg2to compile the largest complete samples of X-ray selected objects to date both in the 0.5-1?keV, 1-2?keV, 2-4.5?keV, 4.5-10?keV bands employed in standard XMM-Newton data processing and in the 0.5-2?keV and 2-10?keV energy bands more usually considered in source count studies. Our survey includes in excess of 30?000?sources and spans fluxes from ~10-15to 10-12?erg?cm-2?s-1below 2?keV and from ~10-14to 10-12?erg?cm-2?s-1above 2?keV where the bulk of the cosmic X-ray background?energy density is produced.Results. The very large sample size we obtained means our results are not limited by cosmic variance or low counting statistics. A break in the source count distributions was detected in all energy bands except the 4.5-10?keV band. We find that an analytical model comprising 2?power-law components cannot adequately describe the curvature seen in the source count distributions. The shape of the logN(>S)?- logS is strongly dependent on the energy band with a general steepening apparent as we move to higher energies. This is due to the fact that non-AGN populations, comprised mainly of stars and clusters of galaxies, contribute up to 30% of the source population at energies <2?keV and at fluxes ?10-13?erg?cm-2?s-1, and these populations of objects have significantly flatter source count distributions than AGN. We find a substantial increase in the relative fraction of hard X-ray sources at higher energies, from ?55% below 2?keV to ?77% above 2?keV. However, the majority of sources detected above 4.5?keV still have significant flux below 2?keV. Comparison with predictions from the synthesis models suggest that the models might be overpredicting the number of faint absorbed AGN, which would call for fine adjustment of some model parameters such as the obscured to unobscured AGN?ratio and/or the distribution of column densities at intermediate obscuration.

Aims.We present the optical classification and redshift of 348 X-ray selected sources from the XMM-Newton Bright Serendipitous Survey (XBS), which contains a total of 400?objects (identification level?=?87%). About?240 are new identifications. In particular, we discuss in detail the classification criteria adopted for the active galactic nuclei (AGNs) population.Methods.By means of systematic spectroscopic campaigns using various telescopes and through the literature search, we have collected an optical spectrum for the large majority of the sources in the XBS survey and applied a well-defined classification ?flow chart?. Results.We find that the AGNs represent the most numerous population at the flux limit of the XBS survey (~10-13?erg?cm-2?s-1) constituting?80% of the XBS sources selected in the 0.5?4.5?keV energy band and?95% of the ?hard? (4.5?7.5?keV) selected objects. Galactic sources populate the 0.5?4.5?keV sample significantly?(17%) and only marginally?(3%) the 4.5?7.5?keV sample. The remaining sources in both samples are clusters/groups of galaxies and normal galaxies (i.e. probably not powered by an AGN). Furthermore, the percentage of type?2 AGNs (i.e. optically absorbed AGNs with AV>2?mag) dramatically increases going from the 0.5?4.5?keV sample (f=NAGN 2/NAGN=7%) to the 4.5?7.5?keV sample (f=32%). We finally propose two simple diagnostic plots that can be easily used to obtain the spectral classification for relatively low-redshift AGNs even if the quality of the spectrum is not good.

We present XMM-Newton data centered on one of the MUNICS Near Infrared Cluster Survey fields (S2F1) and we discuss the X-ray properties of the 6 X-ray emitting EROs found. For one of them we have already obtained the redshift using near-infrared spectroscopic data, while for the remaining 5 EROs the analysis is based on photometric redshifts. We find evidence for the presence of an X-ray obscured QSO in at least 5 out of the 6 X-ray emitting EROs. For these 5 objects we derive intrinsic (2–10 keV) luminosities in excess of 10$^{44}$ erg s$^{-1}$ and intrinsic column densities higher than 10$^{22}$ cm$^{-2}$. These values have been obtained through a basic X-ray spectral analysis for the three brightest sources and through the analysis of the hardness ratios for the remaining two. All of these 5 X-ray emitting EROs appear extended in the optical/near-infrared bands indicating that the host galaxy emission dominates at these wavelengths. This suggests that the hosted AGNs are likely to be absorbed also in the optical/near-infrared bands: i.e. they are likely X-ray obscured possible type 2 QSOs. For the remaining ERO the presence of an AGN is suggested both by its high 0.5–2 keV luminosity ($L_{0.5-2\rm keV}\sim10^{43}$ erg s$^{-1}$) and by its X-ray-to-optical flux ratio. In this case the quality of the present data prevents us from placing firm constraints on the AGN type hosted. Finally, the near-IR spectrum obtained for one of the 6 EROs classifies the host galaxy as an elliptical at $z\simeq1.7$ with a stellar mass well in excess of 10$^{11}$ $M_\odot$. This result corroborates the possible link between the QSO activity and the formation of massive spheroids.

We present BeppoSAX and XMM-Newton observations of Mrk 231. These observations and in particular the BeppoSAX PDS data allowed us to unveil, for the first time, the highly absorbed (NH∼2×1024 cm-2) AGN component. We find that: a) the AGN powering Mrk 231 has an intrinsic 2-10 keV luminosity of 1+1-0.5×1044 erg s-1; b) the strong starburst activity contributes significantly in the 0.1-10 keV energy range. We propose that the starburst activity strongly contributes to the far infrared luminosity of Mrk 231; this is also suggested by the multiwavelength properties of Mrk 231. [Copyright &y& Elsevier]

In this paper, we report the first results of a medium survey program conducted in the 2-10 keV energy band using data from the GIS2 instrument onboard the ASCAsatellite.

Context.X-ray surveys are a key instrument in the study of active galactic nuclei (AGN). Thanks to their penetrating ability, X-rays are able to map the innermost regions close to the central super massive black hole (SMBH) as well as to detect and characterize its emission up to high redshift.Aims.We present here a detailed X-ray spectral analysis of the AGN belonging to the XMM-Newton bright survey (XBS). The XBS is composed of two flux-limited samples selected in the complementary 0.5−4.5 and 4.5−7.5 keV energy bands and comprising more than 300 AGN up to redshift  ~2.4.Methods.We performed an X-ray analysis following two different approaches: by analyzing individually each AGN X-ray spectrum and by constructing average spectra for different AGN types.Results.From the individual analysis, we find that there seems to be an anti correlation between the spectral index and the sources’ hard X-ray luminosity, such that the average photon index for the higher luminosity sources (>1044erg s-1) is significantly (>2σ) flatter than the average for the lower luminosity sources. We also find that the intrinsic column density distribution agrees with AGN unified schemes, although a number of exceptions are found (3% of the whole sample), which are much more common among optically classified type 2 AGN. We also find that the so-called “soft-excess”, apart from the intrinsic absorption, constitutes the principal deviation from a power-law shape in AGN X-ray spectra and it clearly displays different characteristics, and likely a different origin, for unabsorbed and absorbed AGN. Regarding the shape of the average spectra, we find that it is best reproduced by a combination of an unabsorbed (absorbed) power law, a narrow Fe Kαemission line and a small (large) amount of reflection for unabsorbed (absorbed) sources. We do not significantly detect any relativistic contribution to the line emission and we compute an upper limit for its equivalent width (EW) of 230 eV at the 3σconfidence level. Finally, by dividing the type 1 AGN sample into high- and low-luminosity sources, we marginally detect a decrease in the narrow Fe Kαline EWand in the amount of reflection as the luminosity increases, the “so-called” Iwasawa-Taniguchi effect.

The Survey Science Centre of the XMM-Newton satellite released the first incremental version of the 2XMM catalogue in August 2008. Containing more than 220 000 X-ray sources, the 2XMMi was at that time the largest catalogue of X-ray sources ever published and thus constitutes an unprecedented resource for studying the high-energy properties of various classes of X-ray emitters such as AGN and stars. Thanks to the high throughput of the EPIC cameras on board XMM-Newton accurate positions, fluxes, and hardness ratios are available for a substantial fraction of the X-ray detections. The advent of the 7th release of the Sloan Digital Sky Survey offers the opportunity to cross-match two major surveys and extend the spectral energy distribution of many 2XMMi sources towards the optical bands. This implies building extensive homogeneous samples with a statistically controlled rate of spurious matches and completeness. We here present a cross-matching algorithm based on the classical likelihood ratio estimator. The method developed has the advantage of providing true probabilities of identifications without resorting to heavy Monte-Carlo simulations. Over 30,000 2XMMi sources have SDSS counterparts with individual probabilities of identification higher than 90%. At this threshold, the sample has only 2% spurious matches and contains 77% of all expected SDSS identifications. Using spectroscopic identifications from the SDSS DR7 catalogue supplemented by extraction from other catalogues, we build an identified sample from which the way the various classes of X-ray emitters gather in the multi dimensional parameter space can be analysed and later used to design a source classification scheme. We illustrate the interest of this clean source sample by investigating two scientific use cases. In the first example we show how these multi-wavelength data can be used to search for new QSO2s. Although no specific range of observed properties allows us to efficiently identify Compton Thick QSO2s, we show that the prospects are much better for Compton Thin AGN2 and discuss several possible multi-parameter selection strategies. In a second example, we confirm the hardening of the mean X-ray spectrum with increasing X-ray luminosity on a sample of over 500 X-ray active stars and reveal that on average X-ray active M stars display bluer g− rcolour indexes than less active ones. Although this catalogue of 2XMM-SDSS sources cannot be used directly for statistical studies, it nevertheless represents an excellent starting point to select well defined samples of X-ray-emitting objects.

Context.Obscured AGN are fundamental to understand the history of supermassive black hole growth and their influence on galaxy formation. However, the Compton-thick AGN (NH>  1024cm-2) population is basically unconstrained, with less than a few dozen confirmed Compton-thick AGN found and studied so far. A way to select heavily obscured AGN is to compare the X-ray emission below 10 keV (which is strongly depressed) with the emission from other bands that are less affected by the absorption, like the IR band. To this end, we have cross-correlated the 2XMM catalogue with the IRAS Point Source catalogue and, by using the X-ray to infrared flux ratio and X-ray colours, we selected a well defined sample of Compton-thick AGN candidates at z< 0.1.

Arp 299 is a powerful far-IR merging starburst system, composed of IC 694 and NGC 3690. Recent BeppoSAX observations clearly unveiled the presence of a strongly absorbed (NH≃2.5×1024 cm-2) AGN, but at the spatial resolution of BeppoSAX instruments the system was not resolved. Here we present the XMM-Newton observations of Arp 299, which allow us to disentangle the X-ray emission of the two merging galaxies. The detection in both spectra of a hard X-ray emission and of a strong line-like structure in the 6.4–6.7 keV energy range seems to suggest the presence of an AGN in both nuclei. This would be the second discovery of two AGNs in a merging system after NGC 6240 [ApJL 582 (2003) L15]. [Copyright &y& Elsevier]