X-ray Line Emitting Objects in XMM-Newton Observations: the Tip of the Iceberg

We present preliminary results from a novel search for X-ray Line Emitting Objects (XLEOs) in XMM-Newton images. Three sources have been detected in a test-run analysis of 13 XMM-Newton observations. The three objects found are most likely extremely absorbed AGN characterized by a column density NH~10^24cm^-2. Their redshift has been directly determined from the X-ray data, by interpreting the detected emission line as the 6.4 keV Fe line. The measured equivalent width of the X-ray line is, in all three cases, several keV. This pilot study demonstrates the success of our search method and implies that a large sample of XLEOs can be obtained from the public XMM-Newton data archive.Comment: 10 pages, 3 figures, accepted for publication in ApJ Letter

A deep Chandra observation of the interacting star-forming galaxy Arp 299

We present results from a 90 ks Chandra ACIS-S observation of the X-ray luminous interacting galaxy system Arp 299 (NGC 3690/IC 694). We detect 25 discrete X-ray sources with luminosities above 4.0x10^38 erg s^-1 covering the entire Ultra Luminous X-ray source (ULX) regime. Based on the hard X-ray spectra of the non-nuclear discrete sources identified in Arp 299, and their association with young, actively star-forming region of Arp 299 we identify them as HMXBs. We find in total 20 off-nuclear sources with luminosities above the ULX limit, 14 of which are point-like sources. Furthermore we observe a marginally significant deficit in the number of ULXs, with respect to the number expected from scaling relations of X-ray binaries with the star formation rate (SFR). Although the high metalicity of the galaxy could result in lower ULX numbers, the good agreement between the observed total X-ray luminosity of ULXs, and that expected from the relevant scaling relation indicates that this deficit could be the result of confusion effects. The integrated spectrum of the galaxy shows the presence of a hot gaseous component with kT = 0.72+-0.03 keV, contributing 20% of the soft (0.1-2.0 keV) unabsorbed luminosity of the galaxy. A plume of soft X-ray emission in the west of the galaxy indicates a large scale outflow. We find that the AGN in NGC 3690 contributes only 22% of the observed broad-band X-ray luminosity of Arp 299.Comment: 20 pages, 14 figures, 9 tables. Accepted for publication in MNRA

GALEX measurements of the Big Blue Bump as a tool to study bolometric corrections in AGNs

Active Galactic Nuclei emit over the entire electromagnetic spectrum with the peak of the accretion disk emission in the far-UV, a wavelength range historically difficult to investigate. We use here the GALEX (Galaxy Evolution Explorer) Near-UV and Far-UV measurements (complemented with optical data from Sloan Digital Sky Survey (SDSS) and XMM-Newton X-ray spectra) of a sample of 83 X-ray selected type 1 AGN extracted from the XMM-Newton Bright Serendipitous Survey to study their spectral energy distribution (SED) in the optical, Near and Far-UV and X-ray energy bands. We have constrained the luminosity of the accretion disk emission component and calculated the hard X-ray bolometric corrections for a significant sample of AGN spanning a large range in properties (z, L(x)).Comment: 2 pages, 2 figures, To appear in refereed Proceedings of "X-ray Astronomy 2009: Present Status, Multi-Wavelength Approach and Future Perspectives", Bologna, Italy, September 7-11, 2009, AIP, eds. A. Comastri, M. Cappi, and L. Angelin

The role of relativistic jets in the heaviest and most active supermassive black holes at high redshift

In powerful radio-quiet active galactic nuclei (AGN), black holes heavier than one billion solar masses form at a redshift ~1.5-2. Supermassive black holes in jetted radio-loud AGN seems to form earlier, at a redshift close to 4. The ratio of active radio-loud to radio-quiet AGN hosting heavy black holes is therefore a rather a strong function of redshift. We report on some recent evidence supporting this conclusion, gathered from the Burst Alert Telescope (BAT, onboard Swift) and by the Large Area Telescope (LAT, onboard Fermi). We suggest that the more frequent occurrence of relativistic jets in the most massive black holes at high redshifts, compared to later times, could be due to the average black hole spin being greater in the distant past, or else to the jet helping a fast accretion rate (or some combination of the two scenarios). We emphasize that the large total accretion efficiency of rapidly spinning black holes inhibits a fast growth, unless a large fraction of the available gravitational energy of the accreted mass is not converted into radiation, but used to form and maintain a powerful jet.Comment: 6 pages, 3 figures, accepted for publication in MNRAS, main journa

A FIRST DETERMINATION OF THE SURFACE DENSITY OF GALAXY CLUSTERS AT VERY LOW X--RAY FLUXES

We present the first results of a serendipitous search for clusters of galaxies in deep ROSAT-PSPC pointed observations at high galactic latitude. The survey is being carried out using a Wavelet based Detection Algorithm which is not biased against extended, low surface brightness sources. A new flux--diameter limited sample of 10 cluster candidates has been created from $\rm\sim 3 \, deg^2$ surveyed area. Preliminary CCD observations have revealed that a large fraction of these candidates correspond to a visible enhancement in the galaxy surface density, and several others have been identified from other surveys. We believe these sources to be either low--moderate redshift groups or intermediate to high redshift clusters. We show X-ray and optical images of some of the clusters identified to date. We present, for the first time, the derived number density of the galaxy clusters to a flux limit of $\rm 1\cdot 10^{-14} erg cm^{-2} s^{-1}$ (0.5--2.0 keV). This extends the $\log N$--$\log S$ of previous cluster surveys by more than one decade in flux. Results are compared to theoretical predictions for cluster number counts.Comment: uuencoded compressed Postscript, 7 pages including 4 figures. Accepted for publication in Ap. J. Letters

The REX survey: a search for Radio Emitting X-ray sources

We present the scientific goals, the strategy and the first results of the REX project, an effort aimed at creating a sizable and statistically complete sample of Radio Emitting X-ray sources (REX) using the available data from a VLA survey and the ROSAT PSPC archive. Through a positional cross-correlation of the two data sets we have derived a sample of about 1600 REX. Among the 393 REX identified so far a high fraction is represented by AGNs, typically radio loud QSOs and BL Lacs. The remaining sources are galaxies, typically radio galaxies isolated or in cluster. Thanks to the low flux limits in the radio and in the X-ray band and the large area of sky covered by the survey, we intend to derive a new complete and unbiased sample of BL Lacs which will contain both ``RBL'' and ``XBL'' type objects. In this way, the apparent dichotomy resulting from the current samples of BL Lacs will be directly analyzed in a unique sample. Moreover, the high number of BL Lacs expected in the REX sample (about 200) will allow an accurate estimate of their statistical properties. To date, we have discovered 15 new BL Lacs and 11 BL Lac candidates with optical properties intermediate between those of a typical elliptical galaxy and those of a typical BL Lac object. These objects could harbour weak sources of non-thermal continuum in their nuclei and, if confirmed, they could represent the faint tail of the BL Lac population. The existence of such ``weak'' BL Lacs is matter of discussion in recent literature and could lead to a re-assessment of the defining criteria of a BL Lac and, consequently, to a revision of their cosmological and statistical properties.Comment: 30 pages, 13 figures, accepted for publication to Ap

Emission Line AGNs from the REX survey: Results from optical spectroscopy

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.Comment: 27 pages. To be published in Astronomy and Astrophysics, Supplement Series. Better quality figures can be asked to the autho