相关论文: The colours of the X-ray background

We summarise our recent work on the faint galaxy contribution to the cosmic X-ray background (XRB). At bright X-ray fluxes (in the ROSAT pass band), broad line QSOs dominate the X-ray source population, but at fainter fluxes there is…

Models for the origin of the hard X-ray background have suggested that sources with the most accretion activity lie hidden in highly obscured AGN. We report on our study of hard, serendipitous sources in the fields of Chandra clusters with…

Multiwavelength observations of the hard X-ray selected sources discovered by BeppoSAX, Chandra and XMM-Newton surveys have significantly improved our knowledge of the AGN population. The increasing number of X-ray obscured AGN so far…

XMM-Newton spectra of five red, 2MASS AGN, selected from a sample observed by Chandra to be relatively X-ray bright and to cover a range of hardness ratios, confirm the presence of substantial absorbing material in three sources with…

The cosmic X-ray background (CXB), which peaks at an energy of ~30 keV, is produced primarily by emission from accreting supermassive black holes (SMBHs). The CXB therefore serves as a constraint on the integrated SMBH growth in the…

We analyze 18 sources that were found to show interesting properties of periodicity, very soft spectra and/or large long-term variability in X-rays in our project of classification of sources from the 2XMMi-DR3 catalog but were poorly…

We present our first results from 130 ks of X-ray observations obtained with the Advanced CCD Imaging Spectrometer on the Chandra X-ray Observatory. We reach a flux of 2 X 10^(-16) erg s^(-1) cm^(-2) in the 0.5-2 keV soft band and 2 X…

Our goal is to probe the populations of obscured and unobscured AGN investigating their optical-IR and X-ray properties as a function of X-ray flux, luminosity and redshift within a hard X-ray selected sample of 136 X-ray sources in the XMM…

The X-ray Background (XRB) probably originates from the integrated X-ray emission of active galactic nuclei (AGN). Modelling of its flat spectrum implies considerable absorption in most AGN. Compton down-scattering means that sources in…

We present results of an extensive study of the X-ray spectral properties of sources detected in the RIXOS survey, that is nearly complete down to a flux limit of 3e-14 cgs (0.5-2 keV). We show that for X-ray surveys containing sources with…

We report on the results of a detailed analysis of the X-ray spectral properties of a large sample of sources detected serendipitously with the XMM-Newton observatory in 25 selected fields. The survey covers a total solid angle of ~3.5 deg2…

We review the current understanding of the diffuse gamma-ray background (DGRB). The DGRB is what remains of the total measured gamma-ray emission after the subtraction of the resolved sources and of the diffuse Galactic foregrounds. It is…

The cores of active galactic nuclei (AGN) harbor some of the most extreme conditions of matter and energy in the Universe. One of the major goals of high-energy astrophysics is to probe these extreme environments in the vicinity of…

Deep X-ray surveys have shown that the cosmic X-ray background (XRB) is largely due to accretion onto supermassive black holes, integrated over cosmic time. However, the characteristic hard spectrum of the XRB can only be explained if most…

The cosmic X-ray background (CXB) is dominated by the obscured and unobscured coronal light of active galactic nuclei (AGN). At energies below 10 keV, the CXB can be well explained by models taking into account the known AGN and the…

We identify sources with extremely hard X-ray spectra (i.e., with photon indices of Gamma<0.6 in the 13 sq. deg. NuSTAR serendipitous survey, to search for the most highly obscured AGNs detected at >10 keV. Eight extreme NuSTAR sources are…

The X-ray sky is not as well known as is sometimes thought. We report on our search of minority populations (Kim & Elvis 1999). One of the most intriguing is that of `blank field sources', i.e. bright ROSAT sources (F(X)>1e-13 erg/cm2/s)…

We present the first results of ChaMP X-ray source properties obtained from the initial sample of 62 observations. The data have been uniformly reduced and analyzed with techniques specifically developed for the ChaMP and then validated by…

We discuss the constraints on the AGN evolution from the cosmic X-ray background and source counts. A synthesis model to fit the X-ray background is presented. In the model, the spectrum of type 2 AGN has been modeled including Compton…

For the low density filamentary and sheet-like structures in the warm ($\sim 10^4$ to $\sim 10^6$ K) IGM predicted by numerical simulations the resonant line scattering of X-ray background (XRB) photons by He and H-like ions of heavy…