Constraints on models for the high- and low-energy X-ray backgrounds

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The high-energy X-ray background most likely results from unresolved sources, since the model in which the background results from a smooth hot intergalactic medium at semi-relativistic temperatures is ruled out by the COBE measurements. Models in which the high- and low-energy backgrounds are produced by sources are constrained by general arguments based on energetics. In addition, the properties of the sources which produce the low-energy background, and of those producing the high-energy background if the spectrum of these sources extrapolates to low energies, are constrained by the flux and isotropy limits of the Einstein deep survey. The application of the energy, flux, and isotropy constraints depend on the cosmological model, that is, on whether the universe is flat and matter dominated, open, or flat and dominated by a cosmological constant. The flux and isotropy arguments depend directly on the cosmological model, and the energy arguments are indirectly tied to the cosmological model through the Hubble constant. These constraints are discussed and applied to particular models to determine which models are viable sources of the high- and low-energy backgrounds in different cosmological models. Predictions of the models are discussed, as are the constraints which will result from the ROSAT deep survey. Two of the three models considered have difficulty producing the high-energy X-ray background in a flat, matter-dominated universe. The massive black hole model is able to account for the observed characteristics of the high-energy X-ray background in a flat matter dominated universe, but the massive X-ray binary and supernovae models are inconsistent with the observations. In an open universe, or a flat universe dominated by a cosmological constant, both the massive black hole model and the supernovae model are consistent with the constraints and could produce the high-energy background. The low-energy background could be produced by either massive black holes, or supernovae explosions in young galaxies, in any cosmological model. The massive X-ray binary model is only marginally acceptable as a source of the low-energy background and is unlikely to be the source of the high-energy background.

Original languageEnglish (US)
Pages (from-to)37-51
Number of pages15
JournalAstrophysical Journal
Issue number1
StatePublished - Sep 20 1991

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


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