X-ray quasars and the X-ray background

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چکیده ندارد.

The X-ray Background and the Deep X-ray Surveys

The deep X-ray surveys performed by the two major X-ray observatories on flight, Chandra and XMM, are being resolving the bulk of the cosmic X-ray background (XRB) in the 2–10 keV energy band, where the sky flux is dominated by extragalactic emission. Although the actual fraction depends on the absolute sky flux, which is measured with an uncertainty of ∼ 40%, most of the XRB is already resolve...

X-Ray Background Fluctuations

Minor Ha activity, consisting of small brightenings and small, surgelike spikes, was observed to take place above an active center at the solar limb in good time-association with small fluctuations in the soft X-ray background flux, suggesting that even small dynamical events seen optically are associated with coronal heating. The ratio of Ha flux to soft X-ray flux in some of the surges was ap...

The X–ray Background: Observations

X–ray Emission from the First Quasars

It is currently unknown whether the Universe was reionized by quasars or stars at z ∼ > 5. We point out that quasars can be best distinguished from stellar systems by their X-ray emission. Based on a simple hierarchical CDM model, we predict the number counts and X-ray fluxes of quasars at high redshifts. The model is consistent with available data on the luminosity function of high-redshift qu...