A complete X-ray sample of the high latitude sky from HEAO-1 A-2: log N lo S and luminosity functions

An experiment was performed in which a complete X-ray survey of the 8.2 steradians of the sky at galactic latitudes where the absolute value of b is 20 deg down to a limiting sensitivity of 3.1 x ten to the minus 11th power ergs/sq cm sec in the 2-10 keV band. Of the 85 detected sources 17 were identified with galactic objects, 61 were identified with extragalactic objects, and 7 remain unidentified. The log N - log S relation for the non-galactic objects is well fit by the Euclidean relationship. The X-ray spectra of these objects were used to construct log N - log S in physical units. The complete sample of identified sources was used to construct X-ray luminosity functions, using the absolute maximum likelihood method, for clusters galaxies and active galactic nuclei

Statistical properties of local active galactic nuclei inferred from the RXTE 3-20 keV all-sky survey

We compiled a sample of 95 AGNs serendipitously detected in the 3-20 keV band at Galactic latitude |b|>10 during the RXTE slew survey (XSS, Revnivtsev et al.), and utilize it to study the statistical properties of the local population of AGNs, including X-ray luminosity function and absorption distribution. We find that among low X-ray luminosity (Lx < 10^43.5 erg/s) AGNs, the ratio of absorbed (characterized by intrinsic absorption in the range 10^22 cm^-2 < NH < 10^24 cm^-2) and unabsorbed (NH < 10^22 cm^-2) objects is 2:1, while this ratio drops to less than 1:5 for higher luminosity AGNs. The summed X-ray output of AGNs with Lx > 10^41 erg/s estimated here is smaller than the earlier estimated total X-ray volume emissivity in the local Universe, suggesting that a comparable X-ray flux may be produced together by lower luminosity AGNs, non-active galaxies and clusters of galaxies. Finally, we present a sample of 35 AGN candidates, composed of the unidentified XSS sources.Comment: 15 pages, 12 figures. A&A 423, 469. Corrected typos in Table

The BeppoSAX view of the hard X-ray background

First results on a medium-deep X-ray survey in the "new" 5-10 keV band carried out with the MECS detectors onboard BeppoSAX are presented. The High Energy Llarge Area Survey (HELLAS) is aimed to directly explore a band where the energy density of the X-ray background is more than twice than that in the soft (0.5-2.0 keV) band. The optical identification follow-up of the first ten HELLAS hard X-ray sources indicate that Active Galactic Nuclei are the dominant population at 5-10 keV fluxes of the order of 10e-13 cgs. We discuss the implications of these findings for the AGN synthesis models for the XRB.Comment: 6 pages, 4 figures, uses psfig.sty. Accepted for publication in Advances in Space Research, Proceedings of the 32nd Scientific Assembly of COSPA

Investigating the origins of the CMB-XRB cross correlation

Recently, we presented evidence for a cross-correlation of the WMAP satellite map of the cosmic microwave background (CMB) and the HEAO1 satellite map of the hard X-ray background (XRB) with a dimensionless amplitude of 0.14 +- 0.05 normalized to the product of the rms fluctuations of the CMB and XRB (Boughn & Crittenden, 2004). Such a correlation is expected in a universe dominated by a cosmological constant via the integrated Sachs-Wolfe (ISW) effect and the level of the correlation observed is consistent with that predicted by the currently favored Lambda cold dark matter model of the universe. Since this offers independent confirmation of the cosmological model, it is important to verify the origin of the correlation. Here we explore in detail some possible foreground sources of the correlation. The present evidence all supports an ISW origin.Comment: 8 pages, 7 eps figure

Probing the unified model in NGC 7314

We present a study of the complex absorbed X-ray spectrum of the Narrow Line Seyfert 1 galaxy NGC 7314. We collected available public X-ray data from the archives of XMM-Newton, Suzaku, and ASCA. The spectra were analyzed using the fitting package SPEX. We find evidence of intrinsic neutral and ionized absorption in the XMM-Newton EPIC-pn spectrum. The ionized gas presents three significantly distinct ionization phases, although its kinematic properties could not be disentangled. At least two of these phases are also detected in the RGS spectrum, although with less significance due to the low statistics. The ASCA and Suzaku spectra show larger neutral absorption but no ionized gas signatures. The Fe Kalpha emission line is detected in all the observations and, additionally, Fe XXVI in the EPIC-pn spectrum, and Fe Kbeta in the Suzaku XIS spectrum. Using this observational evidence we construct a consistent picture of the geometry of the system in the context of the unified model of active galactic nuclei. The different observational properties are thus interpreted as clouds of neutral gas moving across our line of sight, which would be grazing a clumpy dusty torus.Comment: 9 pages, 8 figures. Accepted for publication in Astronomy and Astrophysic

Broadband X-ray spectrum of GRS 1734-292, a luminous Seyfert 1 galaxy behind the Galactic Center

Based on a deep survey of the Galactic Center region performed with the INTEGRAL observatory, we measured for the first time the hard X-ray (20-200 keV) spectrum of the Seyfert 1 galaxy GRS 1734-292 located in the direction of the Galactic Center. We extended the spectrum to lower energies using archival GRANAT and ASCA observations. The broadband X-ray spectrum is similar to those of other nearby luminous AGNs, having a power law shape without cutoff up to at least 100 keV.Comment: 4 pages, 3 figures. Accepted for publication in A&A Letter

Large-scale variations of the cosmic X-ray background and the X-ray emissivity of the local Universe

We study the cosmic X-ray background (CXB) intensity variations on large angular scales using slew data of the RXTE observatory. We detect intensity variations up to ~2% on angular scales of 20--40deg. These variations are partly correlated with the local large-scale structure, which allowed us to estimate the emissivity of the local Universe in the energy band 2--10 keV at 9+/-4 x 10^{38} ers/sec/Mpc^{3}. The spectral energy distribution of the large-angular-scale variations is hard and is compatible with that of the CXB, which implies that normal galaxies and clusters of galaxies, whose spectra are typically much softer, do not contribute more than 15% to the total X-ray emissivity of the local Universe. Most of the observed CXB anisotropy (after exclusion of point sources with fluxes >10^{-11} erg/s/cm^2) can be attributed to low-luminosity AGNsComment: 12 pages, 9 figures, Submitted to A&

The Lx-T and Lx-sigma Relationships for Galaxy Clusters Revisited

The relationships between the X-ray determined bolometric luminosity Lx, the temperature T of the intracluster gas, and the optical measured velocity dispersion sigma of the cluster galaxies are updated for galaxy clusters using the largest sample of 256 clusters drawn from literature. The newly established relationships, based on the doubly weighted orthogonal distance regression (ODR) method, are justified by both their self-consistency and co-consistency, which can then be used to test the theoretical models of cluster formation and evolution. The observationally determined Lx-T and Lx-sigma relationships, $L_x\propto T^{2.72\pm0.05}\propto \sigma^{5.24\pm0.29}$, are marginally consistent with those predicted in the scenario that both intracluster gas and galaxies are in isothermal and hydrostatic equilibrium with the underlying gravitational potential of clusters. A comparison between these observed and predicted Lx-T relationships also suggests that the mean cluster baryon fraction fb remains approximately constant among different clusters, $f_b\approx0.17$, which gives rise to a low-mass density universe of $\Omega_m\approx0.3$.Comment: 34 pages, 7 figures, 2 tables, accepted for publication in Ap

The origin of the iron lines in NGC 7213

The analysis of a simultaneous XMM-Newton/BeppoSAX plus three previous BeppoSAX observations revealed that NGC 7213 is a rather peculiar Seyfert 1. No significant Compton reflection component was observed, while an iron line complex, best explained in terms of three narrow lines, is clearly apparent in the data. Due to the absence of the reflection component, the neutral iron line is likely not produced in a Compton-thick material, but current data do not allow to choose between a Compton-thin torus and the BLR. The two ionized iron lines from \ion{Fe}{xxv} and \ion{Fe}{xxvi} may be produced in a photoionized gas with a column density of a few 10$^{23}$ cm$^{-2}$, in analogy with the case of NGC 5506.Comment: 4 pages, 4 figures, accepted for publication in A&A Letter

An XMM-Newton view of the `bare' nucleus of Fairall 9

We present the spectral results from a 130 ks observation, obtained from the X-ray Multi-Mirror Mission-Newton (XMM-Newton) observatory, of the type I Seyfert galaxy Fairall 9. An X-ray hardness-ratio analysis of the light-curves, reveals a `softer-when-brighter' behaviour which is typical for radio-quiet type I Seyfert galaxies. Moreover, we analyse the high spectral-resolution data of the reflection grating spectrometer and we did not find any significant evidence supporting the presence of warm-absorber in the low X-ray energy part of the source's spectrum. This means that the central nucleus of Fairall 9 is `clean' and thus its X-ray spectral properties probe directly the physical conditions of the central engine. The overall X-ray spectrum in the 0.5-10 keV energy-range, derived from the EPIC data, can be modelled by a relativistically blurred disc-reflection model. This spectral model yields for Fairall 9 an intermediate black-hole best-fit spin parameter of $\alpha=0.39^{+0.48}_{-0.30}$.Comment: Accepted for publication in MNRAS. The paper contains 11 figures and 1 tabl