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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 andXMM–Newton observations, we cannot infer the possible location of the obscuring material causing the observed variability. In the 6–7 keV range, theXMM–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

According to the latest versions of synthesis modeling of the Cosmic X-ray Background, Compton-thick AGN should represent ~50 % of the total absorbed AGN population. However, despite their importance in the cosmological context, only a few dozens of Compton-thick AGN have been found and studied so far. We will briefly review this topic and discuss the improvement in this field offered by the Simbol-X mission with its leap in sensitivity (E>10 keV) of more than a factor 500 with respect to previous X-ray missions.

We analyze the ROSAT Deep Cluster Survey (RDCS) to derive cosmological constraints from the evolution of the cluster X-ray luminosity distribution. The sample contains 103 galaxy clusters out to z=0.85 and flux-limit Flim=3 10^{-14} cgs (RDCS-3) in the [0.5-2.0] keV energy band, with a high-z extension containing four clusters at 0.901 10^{-14} cgs (RDCS-1). Model predictions for the cluster mass function are converted into the X-ray luminosity function in two steps. First we convert mass into intra-cluster gas temperature by assuming hydrostatic equilibrium. Then temperature is converted into X-ray luminosity by using the most recent data on the Lx-T relation for nearby and distant clusters. These include the Chandra data for seven distant clusters at 0.57, Comment: 10 pages, 4 figures, to appear in Astrophysical Journal

With its large collection area, broad-band energy coverage from optical/NIR (0.3 to 2.2 micron) to soft/hard X-ray (0.1-600 keV), all-sky monitoring capability, and on-board follow-up, the proposed Energetic X-ray Imaging Survey Telescope mission (EXIST, see L. Natalucci contribution at this conference) has been designed to properly tackle the study of the AGN phenomenon and the role that SMBH play in the Universe. In particular EXIST will carry out an unprecedented survey above 10 keV (a factor ~20 increase in hard X-ray sensitivity compared to current and prior X-ray missions) of SMBH activity, not just in space but also in time and over a significant expanded energy range; this strategy will overcome previous selection biases, will break the "multi-wavelength" identification bottleneck and will dramatically increase the number of AGN detected above 10 keV that are amenable to detailed follow-up studies (~50000 AGN are expected). We discuss here on few selected AGN science topics enabled by the unique combination of EXIST's instruments. In particular EXIST will enable major progress in understanding: i) when and where SMBH are active in the Universe (by revealing and measuring heavily obscured accretion in the local - z, 6 pages, 2 figures. Proc. of Workshop "The Extreme sky: Sampling the Universe above 10 keV", Otranto (Lecce) Italy, October 13-17, 2009 Proceedings of Science, http://pos.sissa.it. Submitted version

[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. [Methods]: The 2XMM catalogue has been compiled from a new processing of the XMM-Newton EPIC camera data. The main features of the processing pipeline are described in detail. [Results]: The catalogue, the largest ever made at X-ray wavelengths, contains 246 897 detections drawn from 3491 public XMM-Newton observations over a 7-year interval, which relate to 191 870 unique sources. The catalogue fields cover a sky area of more than 500 deg2. The non-overlapping sky area is ∼360 deg2 (∼1% of the sky) as many regions of the sky are observed more than once by XMM-Newton. The catalogue probes a large sky area at the flux limit where the bulk of the objects that contribute to the X-ray background lie and provides a major resource for generating large, well-defined X-ray selected source samples, studying the X-ray source population and identifying rare object types. The main characteristics of the catalogue are presented, including its photometric and astrometric properties., M. Ceballos, F. Carrera and X. Barcons acknowledge financial support by the Spanish Ministerio de Educacion y Ciencia under projects ESP2003-00812 and ESP2006-13608-C02-01. The French teams are grateful to CNES for supporting this activity. In Germany the XMM-Newton project is supported by the Bundesministerium für Wirtschaft und Technologie/Deutsches Zentrum für Luft und Raumfahrt e.V. (DLR) and the Max Planck Society. Part of this work was supported by the DLR project numbers 50 OX 0201, 50 OX 0001, and 50 OG 0502. The Italian team acknowledges financial support from the Agenzia Spaziale Italiana (ASI), the Ministero dell’ Istruzione, Università e Ricerca (MIUR) and the Istituto Nazionale di Astrofisica (INAF) over the last years; they are currently supported by the grant PRIN-MIUR 2006-02-5203 and by the ASI grants n.I/088/06/0 and n.I/023/05/0. UK authors thank STFC for financial support.

[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. [Methods]: The 2XMM catalogue has been compiled from a new processing of the XMM-Newton EPIC camera data. The main features of the processing pipeline are described in detail. [Results]: The catalogue, the largest ever made at X-ray wavelengths, contains 246 897 detections drawn from 3491 public XMM-Newton observations over a 7-year interval, which relate to 191 870 unique sources. The catalogue fields cover a sky area of more than 500 deg2. The non-overlapping sky area is ∼360 deg2 (∼1% of the sky) as many regions of the sky are observed more than once by XMM-Newton. The catalogue probes a large sky area at the flux limit where the bulk of the objects that contribute to the X-ray background lie and provides a major resource for generating large, well-defined X-ray selected source samples, studying the X-ray source population and identifying rare object types. The main characteristics of the catalogue are presented, including its photometric and astrometric properties. M. Ceballos, F. Carrera and X. Barcons acknowledge financial support by the Spanish Ministerio de Educacion y Ciencia under projects ESP2003-00812 and ESP2006-13608-C02-01. The French teams are grateful to CNES for supporting this activity. In Germany the XMM-Newton project is supported by the Bundesministerium für Wirtschaft und Technologie/Deutsches Zentrum für Luft und Raumfahrt e.V. (DLR) and the Max Planck Society. Part of this work was supported by the DLR project numbers 50 OX 0201, 50 OX 0001, and 50 OG 0502. The Italian team acknowledges financial support from the Agenzia Spaziale Italiana (ASI), the Ministero dell’ Istruzione, Università e Ricerca (MIUR) and the Istituto Nazionale di Astrofisica (INAF) over the last years; they are currently supported by the grant PRIN-MIUR 2006-02-5203 and by the ASI grants n.I/088/06/0 and n.I/023/05/0. UK authors thank STFC for financial support.

We present observations in the 0.1-100 keV spectral band of 8 Seyfert 2 galaxies, obtained by means of BeppoSAX. These sources were selected according to their [OIII] optical emission line flux, to avoid biases against obscuration on the pc scale. All sources were detected. All of them are weak X-ray emitters, and most of them are characterized by prominent iron lines at 6.4-7 keV (EW > 500 eV) and by a flat continuum, indicative of heavy obscuration along our line of sight (N_H > 10^25 cm^-2 in most cases). These results 1) provide further evidence in favor of the unified scenario, and 2) indicate that the average obscuration of type 2 AGNs is very likely much higher than deduced by former X-ray surveys. These findings have important implications for the synthesis of the X-ray background., 15 pages, 7 figs. Accepted for publication by A&A. Typos in tables corrected. Fig. 5 modified

[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-2s-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 2$]]> mag) dramatically increases going from the 0.5-4.5 keV sample (%) to the 4.5-7.5 keV sample (%). 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. A.C., R.D.C., T.M., and P.S. acknowledge financial support from the MIUR, grant PRIN-MUR 2006-02-5203 and from the Italian Space Agency (ASI), grants n. I/088/06/0 and n. I/023/05/0.

[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-2s-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 2$]]> mag) dramatically increases going from the 0.5-4.5 keV sample (%) to the 4.5-7.5 keV sample (%). 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., A.C., R.D.C., T.M., and P.S. acknowledge financial support from the MIUR, grant PRIN-MUR 2006-02-5203 and from the Italian Space Agency (ASI), grants n. I/088/06/0 and n. I/023/05/0.

[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 have studied the X-ray source counts in four energy bands: soft (0.5-2 keV), hard (2-10 keV), XID (0.5-4.5 keV) and ultra-hard (4.5-7.5 keV) in order to evaluate the contribution of sources at different fluxes to the X-ray background. We have also studied the angular clustering of X-ray sources in those bands. [Methods]: AXIS (An XMM-Newton International Survey) is a survey of 36 high Galactic latitude XMM-Newton observations covering 4.8 deg2 in the Northern sky and containing 1433 serendipitous X-ray sources detected with 5-σ significance. This survey has similar depth to the XMM-Newton catalogues and therefore serves as a pathfinder to explore their possibilities. We have combined this survey with shallower and deeper surveys, and fitted the source counts with a Maximum Likelihood technique. Using only AXIS sources we have studied the angular correlation using a novel robust technique. [Results]: Our source counts results are compatible with most previous samples in the soft, XID, ultra-hard and hard bands. We have improved on previous results in the hard band. The fractions of the XRB resolved in the surveys used in this work are 87%, 85%, 60% and 25% in the soft, hard, XID and ultra-hard bands, respectively. Extrapolation of our source counts to zero flux is not sufficient to saturate the XRB intensity. Only galaxies and/or absorbed AGN could contribute the remaining unresolved XRB intensity. Our results are compatible, within the errors, with recent revisions of the XRB intensity in the soft and hard bands. The maximum fractional contribution to the XRB comes from fluxes within about a decade of the break in the source counts (∼10-14 cgs), reaching ∼50% of the total in the soft and hard bands. Angular clustering (widely distributed over the sky and not confined to a few deep fields) is detected at 99-99.9% significance in the soft and XID bands, with no detection in the hard and ultra-hard band (probably due to the smaller number of sources). We cannot confirm the detection of significantly stronger clustering in the hard-spectrum hard sources. [Conclusions]: Medium depth surveys such as AXIS are essential to determine the evolution of the X-ray emission in the Universe below 10 keV. © ESO 2007. Financial support for this work was provided by the Spanish Ministerio de Educación y Ciencia under projects ESP2003-00812 and ESP2006-13608-C02-01. This research has made use of the USNO-A2.0 catalogue, maintained at the U.S. Naval Observatory. SM, MP, MW, JT and SR acknowledge financial support for this research from PPARC. RDC and TM received partial financial support from the Italian Space Agency under contract ASI-INAF n. I/023/05/0.

[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 have studied the X-ray source counts in four energy bands: soft (0.5-2 keV), hard (2-10 keV), XID (0.5-4.5 keV) and ultra-hard (4.5-7.5 keV) in order to evaluate the contribution of sources at different fluxes to the X-ray background. We have also studied the angular clustering of X-ray sources in those bands. [Methods]: AXIS (An XMM-Newton International Survey) is a survey of 36 high Galactic latitude XMM-Newton observations covering 4.8 deg2 in the Northern sky and containing 1433 serendipitous X-ray sources detected with 5-σ significance. This survey has similar depth to the XMM-Newton catalogues and therefore serves as a pathfinder to explore their possibilities. We have combined this survey with shallower and deeper surveys, and fitted the source counts with a Maximum Likelihood technique. Using only AXIS sources we have studied the angular correlation using a novel robust technique. [Results]: Our source counts results are compatible with most previous samples in the soft, XID, ultra-hard and hard bands. We have improved on previous results in the hard band. The fractions of the XRB resolved in the surveys used in this work are 87%, 85%, 60% and 25% in the soft, hard, XID and ultra-hard bands, respectively. Extrapolation of our source counts to zero flux is not sufficient to saturate the XRB intensity. Only galaxies and/or absorbed AGN could contribute the remaining unresolved XRB intensity. Our results are compatible, within the errors, with recent revisions of the XRB intensity in the soft and hard bands. The maximum fractional contribution to the XRB comes from fluxes within about a decade of the break in the source counts (∼10-14 cgs), reaching ∼50% of the total in the soft and hard bands. Angular clustering (widely distributed over the sky and not confined to a few deep fields) is detected at 99-99.9% significance in the soft and XID bands, with no detection in the hard and ultra-hard band (probably due to the smaller number of sources). We cannot confirm the detection of significantly stronger clustering in the hard-spectrum hard sources. [Conclusions]: Medium depth surveys such as AXIS are essential to determine the evolution of the X-ray emission in the Universe below 10 keV. © ESO 2007., Financial support for this work was provided by the Spanish Ministerio de Educación y Ciencia under projects ESP2003-00812 and ESP2006-13608-C02-01. This research has made use of the USNO-A2.0 catalogue, maintained at the U.S. Naval Observatory. SM, MP, MW, JT and SR acknowledge financial support for this research from PPARC. RDC and TM received partial financial support from the Italian Space Agency under contract ASI-INAF n. I/023/05/0.

We summarize here the current status of the XMM BSS: a large (about 1000 sources) sample of bright serendipitous XMM sources at high galactic latitude (|b| > 20 deg)., Comment: On the behalf of the XMM-Newton Survey Science Centre (SSC) CONSORTIUM, 4 pages, 1 figure, Presented at AGN05: Inflows, Outflows and Reprocessing around black holes, Como (Italy), 11-14 June 2002. To appear in the Proceedings

Using a long (=150 ksec), broad-band (0.1--40 keV) BeppoSAX observation of the merging starburst system Arp 299 (=IC 694 + NGC 3690) we found the first unambiguous evidence of the presence of a deeply buried (N_H = 2.5E24 cm-2) AGN having an intrinsic luminosity of L(0.5-100 keV) = 1.9E43 cgs. The X-ray spectral properties of this AGN are discussed in detail as well as the thermal component detected at soft X-ray energies which, most likely, is associated with the starburst., 4 pages, 2 figures, Latex manuscript, Accepted for publication in Astrophysical Journal - Letters Edition

We present preliminary results of XMM-Newton observations of 5 Ultra-luminous Infrared Galaxies (ULIRGs), part of a mini-survey program dedicated to 10 ULIRGs selected from the bright IRAS sample. For 3 of them (IRAS 20551-4250, IRAS 19254-7245 and Mkn 231) we find strong evidence for the presence of a hidden AGN, while for two others (IRAS 20110-4156 IRAS 22491-1808) the S/N ratio of the data does not allow us to be conclusive. In particular, we have detected a strong Fe-K line in the X-ray spectra of IRAS19254-7245, with an equivalent width (~2 keV) suggestive that most of the energy source in this object is due to a deeply buried AGN., Comment: 4 pages, 3 figures, Latex manuscript, Proc. Symnposium ``New Visions of the X-ray Universe in the XMM-Newton and Chandra Era", 26-30 November 2001, ESTEC, The Netherlands

We study the cosmological evolution of BL Lac objects by applying the Ve/Va analysis to a new sample of 55 objects, presented for the first time in this paper. This sample has been selected from the 239 sources with the brightest X-ray flux (>=4×10-13 ergs s-1 cm-2) and relatively bright optical counterparts (B

We present the first results on the identifications of a medium sensitivity survey (X-ray flux limit 2 × 10-14 erg cm-2s-1 in the 0.5-4.5 keV band) at high galactic latitude (|b| > 20°) 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 deg2 (source density 113±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 ∼ 1.8 and z ∼ 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., XB, FJC, MTC and SM acknowledge financial support by the Spanish MCYT under project AYA2000-1690. RDC and TM acknowledge partial financial support by the Italian Space Agency (ASI) and by the MURST (Cofin00-32-36). This project was supported by the DLR under grants 50 OR 9908 0 (GPS) and 50 OX 9801 3 (HB).

We present the results obtained with BeppoSAX observations of the three Composite Seyfert/star-forming galaxies: IRAS 20051-1117, IRAS 04392-0123 and IRAS 01072+4954. These sources belong to an enigmatic class of X-ray sources detected in the ROSAT All-Sky Survey (Moran et al. 1996) which is composed of 6 low redshift galaxies. Their optical spectra are dominated by the features of HII galaxies while their X-ray luminosities (< 10^{42} ergs/s) are typical of Seyfert galaxies. IRAS 20051-1117 shows a 2-10 keV spectrum well described by a power-law with photon index = 1.9 and low intrinsic absorption. This result, the ratio Flux(2-10 keV)/Flux([OIII]) and the significant X-ray variability detected, clearly rule out a Compton thick nature of this source. IRAS 04392-0123 and IRAS 01072+4954, instead, have a BeppoSAX flux a factor of ~ 50-80 smaller than in the previous ROSAT observations, resulting in poor statistics, that prevents detailed modeling., 4 pages, 2 figures. To appear in "Carnegie Observatories Astrophysics Series, Vol. 1: Coevolution of Black Holes and Galaxies," ed. L. C. Ho (Pasadena: Carnegie Observatories, http://www.ociw.edu/ociw/symposia/series/symposium1/proceedings.html)

We report here preliminary results from a survey of nearby Seyfert galaxies using the EPIC CCDs on board XMM-Newton. The total sample consists of 28 Seyfert galaxies, and constitute a well-defined, complete (B 0 deg.) hemisphere. The survey has been initiated in June, 2001, and we report here the results for the 6 objects analyzed so far, namely: NGC3185, NGC3486, NGC3941, NGC4138, NGC4565, and NGC5033. The main goal of this survey is to obtain a better and unbiased understanding of the ``typical'' Seyfert X-ray spectrum (e.g. the distribution of their absorption column density) in the local Universe. This is crucial to verify the predictions and, thus, to validate unified models, and is a fundamental parameter of synthesis models for the X-ray background. A companion poster (paper II: L. Foschini et al., these proceedings) illustrates how this survey will also allow a comprehensive spectral study of the brightest (highest-luminosity) off-nuclear sources in the galaxies., 4 pages, included 6 figures, to appear in the Proceedings of the Symposium "New Visions of the X-ray Universe in the XMM-Newton and Chandra Era", 26-30 November 2001, ESTEC, The Netherlands

The XMM-Newton Survey Science Center is constructing a large (~1000 sources) and complete sample of bright serendipitous XMM-Newton sources at high galactic latitude, so as to allow both the discovery of sources of high individual interest as well as statistical population studies. The sample, known as ``The XMM-Newton Bright Serendipitous Source Sample" (XMM-Newton BSS), has a flux limit of ~10^(-13) cgs in the 0.5--4.5 keV energy band and will be fundamental in complementing other medium and deep survey programs (having fluxes 10 to 100 times fainter) in order to: a) characterize the X-ray sky and its constituents, b) understand the evolution of the population selected and c) define statistical identification procedures to select rare and interesting populations of X-ray sources (e.g. high z clusters of galaxies, BL Lacs, type 2 QSOs, etc..). We discuss here the scientific rationale and the details of the project and we present some preliminary results., Comment: 8 pages, 5 figures, Latex manuscript, Proc. Symnposium ``New Visions of the X-ray Universe in the XMM-Newton and Chandra Era", 26-30 November 2001, ESTEC, The Netherlands

We study the cosmological evolution of BL Lac objects by applying the Ve/Va analysis to a new sample of 55 objects presented for the first time in this paper. This sample has been selected from the 239 sources with the brightest X-ray flux (>4X10^-13 erg s^-1 cm^-2) and relatively bright optical counterpart (B, Accepted for publication in Part 1 of The Astrophysical Journal

We present BeppoSAX observations of the Southern S1 region in the European Large Area ISO Survey (ELAIS). These observations cover an area of ~1.7 sq. deg. and reach an on-axis (~0.7 sq. deg) 2-10 keV (HX) sensitivity of ~10E-13 cgs. This is the first HX analysis of an ISOCAM survey. We detect 9 sources with a signal to noise ratio SNR_HX>3, 4 additional sources with a 1.3 to 10 keV (T) SNR_T>3 and 2 additional sources which appear to be associated with QSOs with SNR_T>2.9. The number densities of the SNR_HX>3 sources are consistent with the ASCA and BeppoSAX logN-logS functions. Six BeppoSAX sources have reliable ISOCAM 15 micron counterparts within ~60 arcsec. All these ISOCAM sources have optical counterparts of R, 27 pages (draft format), 10 figures, ApJ, in press (May 20 edition)