The anisotropy of the diffuse cosmic X-ray background

From the new data of the 2–60 keV diffuse X-ray background from HEAO-1 A2, model galactic component is subtracted to give the cosmic component. The greater intensity in the northern galactic hemipshere is shown to be probably due to the motion of the Sun relative to the background (the Compton-Getting effect). The derived degree of anisotropy is δ = (0.45 ± 0.18)% and the velocity is V = (397 ± 159) km/s. These values are consistent with the known anisotropy in the microwave background.     

The cosmic microwave background may be produced by particle decay in steady-state cosmology

A theory of electron impact polarization observed in a direction normal to the direction of incident electron was developed by Percival and Seaton. Chambe and Hénoux modified the expression for Stokes parameterQ so that the polarization in a direction making an angle θ with the direction of impact electron could be calculated. A limitation to the idea of Chambe and Hénoux has been discussed.     

Boltzmann approach to the large-angle cosmic X-ray background fluctuations

Large-angle fluctuations in the cosmic X-ray background are investigated by a new formalism with a simple model of the X-ray sources. Our method is formulated from the Boltzmann equation and a simple extension of the work by Lahav et al. to be applicable to a hyperbolic (open) universe. The low multipole fluctuations due to the source clustering are analysed in various cosmological models in both numerical and analytic ways. The fluctuations strongly depend on the X-ray source evolution model, as pointed out previously. It turns out that the nearby ( z  ≲ 0.1) sources are the dominant contributors to the large-angle fluctuations. If these nearby sources are removed in an observed X-ray map, the dipole (low multipole) moment of the fluctuation drastically decreases. In this case the Compton–Getting effect of an observer's motion can be a dominant contribution to the dipole fluctuation. This feature of fluctuation, relating to the matter power spectrum, is discussed.     

Measurements of the cosmic X-ray background of the Universe and the MVN experiment

The paper is devoted to studying the cosmic X-ray background (CXB) of the Universe in the energy range 1–100 keV and to the prospects for its investigation by means of the projected MVN (Monitor Vsego Neba) experiment. The nature of the CXB and its use for studying the cosmological evolution of black holes are briefly discussed. The bulk of the paper is devoted to the methods of CXB measurements, from the first pioneering rocket and balloon-borne experiments to the measurements made with latest-generation orbital X-ray observatories. Particular attention is given to the problems of allowance for the contribution of background events to the measurements with X-ray and hard X-ray instruments.     

The diffuse cosmic X-ray background spectrum in the 2–10 keV energy range

We report a measurement of the background spectrum based on 10000 counts observed in the energy range 2–10 keV. The rocketborne detector system was optimised for cosmic ray noise rejection. A best fit power law spectrum $$\frac{{dN}}{{dE}} = 16E^{ - 1.8} photons{\text{ }}cm^{ - 2} s^{ - 1} sr^{ - 1} keV^{ - 1} .$$ resulted from the analysis. At 10 keV this result is consistent with recently assessed higher energy data. We show therefore that the change in spectral index between 5 and 50 ke V is approximately ?0.2.     

Analysis of the cosmic radio background in the domain of spatial frequencies

Since extra-Galactic radio sources are distributed unevenly over the celestial sphere, accumulated experimental data in the domain of spatial frequencies are used. The author was unable to explain discrepancies between experimental and model spectra by errors of calculation or experiment. A possible explanation is the presence of Galactic fluctuations in the cosmic radio background. Translated from Astrofizika, Vol. 43, No. 3, pp. 451-462, July–September, 2000.     

Wavelet domain Bayesian denoising of string signal in the cosmic microwave background

An algorithm is proposed for denoising the signal induced by cosmic strings in the cosmic microwave background. A Bayesian approach is taken, based on modelling the string signal in the wavelet domain with generalized Gaussian distributions. Good performance of the algorithm is demonstrated by simulated experiments at arcminute resolution under noise conditions including primary and secondary cosmic microwave background anisotropies, as well as instrumental noise.     

Earth X-ray albedo for cosmic X-ray background radiation in the 1–1000 keV band

We present calculations of the reflection of the cosmic X-ray background (CXB) by the Earth's atmosphere in the 1–1000 keV energy range. The calculations include Compton scattering and X-ray fluorescent emission and are based on a realistic chemical composition of the atmosphere. Such calculations are relevant for CXB studies using the Earth as an obscuring screen (as was recently done by INTEGRAL ). The Earth's reflectivity is further compared with that of the Sun and the Moon – the two other objects in the Solar system subtending a large solid angle on the sky, as needed for CXB studies.     

The interrelationship between cosmic dust and the microwave background

Attention is given to the radiation of microwaves by charged dust in space. Presently-used particle distributions do not restrict the presence in space of large numbers of small (r<10^–6 cm) silicate grains, but it is shown that such densities (10^–25–10^–26 g cm^–3) of small grains would produce a microwave background with an energy density of the same order of magnitude as the energy density of the (presumed) cosmological 3 K background. Limits set by the isotropy of the latter are: (HI clouds)10^–26, (Galactic plane)10^–30, (Halo)10^–32, (Local Group)10^–34 g cm^–3. These limits imply that either there is a cutoff in particle distributions atr10^–6 cm, or that the density of silicate grains in space has been generally overestimated, or that cosmic rays have broken up a lot of grains so that they now form a population of grains of very small size (10^–7 cm) which are difficult to detect by conventional methods. One way to look for the latter population is by studying expected distortions of the 3 K spectrum to the short wavelength side of the portion hitherto observed (grains may have a size distribution able to give an approximate black-body curve for radiation from larger grains of 10^–6 cm size), and by testing the effective energy density of the 3 K field in other galaxies.     

The dipole anisotropy of the cosmic microwave background radiation

We review the prediction, discovery and precise measurements of CMB Dipole Anisotropy, a field in which Dennis Sciama has provided important initial insight.     

The shape of the diffuse cosmic X-ray spectrum

Recent work by Dyer and Morfill has shown that satellite measurements of the diffuse cosmic X-ray spectrum made with crystal scintillators may include errors due to radioactive spallation products formed in the detector by inner belt and cosmic ray protons.

An estimate is made of the magnitude of this source of background for the various experimental situations and it is shown that apparent features at 40 keV and 1 MeV are likely to be due to radioactive decays in the instruments. A review is made of experiments covering the range 1 keV-100 MeV in order to ascertain whether a single exponent spectrum is capable of fitting the experimental results. The astrophysical implications of such a spectrum are briefly considered.

Suggestions are made for the location and correction for background of future experiments.

     

Polarization of the cosmic background radiation and secondary ionization of the cosmic medium

We discuss the properties of the cosmic background polarization as predicted by secondary ionization models, and the prospects for the determination of reheating parameters from forthcoming space experiments.     

Intergalactic shock acceleration and the cosmic gamma-ray background

We investigate numerically the contribution to the cosmic gamma-ray background from cosmic-ray ions and electrons accelerated at intergalactic shocks associated with cosmological structure formation. We show that the kinetic energy of accretion flows in the low-redshift intergalactic medium is thermalized primarily through moderately strong shocks, which allow for an efficient conversion of shock ram pressure into cosmic-ray pressure. Cosmic rays accelerated at these shocks produce a diffuse gamma-ray flux which is dominated by inverse Compton emission from electrons scattering off cosmic microwave background photons. Decay of neutral π mesons generated in p–p inelastic collisions of the ionic cosmic-ray component with the thermal gas contribute about 30 per cent of the computed emission. Based on experimental upper limits on the photon flux above 100 MeV from nearby clusters we constrain the efficiency of conversion of shock ram pressure into relativistic CR electrons to  ≲1 per cent  . Thus, we find that cosmic rays of cosmological origin can generate an overall significant fraction of order 20 per cent and no more than 30 per cent of the measured gamma-ray background.