Showing papers by "A. C. Fabian published in 1979"

Einstein observations of the X-ray structure of Centaurus A: evidence for the radio-lobe energy source.

Abstract: The X-ray source at the center of the radio galaxy Centaurus A has been resolved into the following components with the imaging detectors on board the Einstein X-ray Observatory: (1) a point source coincident with the infrared nucleus; (2) diffuse X-ray emission coinciding with the inner radio lobes; (3) a 4-arcmin extended region of emission about the nucleus; and (4) an X-ray jet between the nucleus and the NE inner radio lobe. The 2 x 10 to the 39th ergs/s detected from the radio lobes probably arises from inverse Compton scattering of the microwave background. The average magnetic field in the SW lobe is determined to be not less than 4 microgauss. The extended region may be due to emission by a cloud of hot gas, cosmic-ray scattering, or stellar sources. The jet provides strong evidence for the continuous resupply of energy to the lobes from the nucleus.

High-resolution X-ray observations of the Cassiopeia A supernova remnant with the Einstein Observatory

Abstract: Cas A was observed with the imaging detectors on the Einstein X-ray Observatory. The mass of the expanding shell due to the interaction of the blast wave and the ambient medium is determined. This indicates that Cas A is probably not in the free expansion phase, but has not yet reached the adiabatic phase of expansion. Detailed comparison of X-ray, optical, and radio images shows various degrees of correlation, indicating that several processes for emission are present. An upper limit of 1,500,000 K is established for any stellar remnant that is below the expected temperature of a neutron star by a factor of about 5. The total mass of the SNR is found to be 10-30 solar masses

On the detection of large-scale inhomogeneities in the Universe

Abstract: THE detection of large-scale inhomogeneities in the Universe has proceeded along a number of fronts. The observed spatial distribution of galaxies indicates clumping of matter on length scales up to ∼30 Mpc (ref. 1). Limits on fine-scale temperature fluctuations in the microwave background2 constrain mass concentrations at the epoch of recombination, and later3,4. Neither of these methods is particularly sensitive to large-scale low-density contrast (δρ/ρ ≪ 1), perturbations at the current epoch (that is, masses ≫ 1019 M⊙ on a scale ≳1,000 Mpc), although in principle the distribution of discrete radio sources on the sky may be investigated for such effects (see for example ref. 5). We show here that measurements of the isotropy of the X-ray background provide a sensitive means of detecting such large-scale inhomogeneities within Z ∼ 5.

Large-scale structure of X-ray clusters of galaxies

Abstract: Observations from the A-2 experiment on HEAO-1 are used to search for very large-scale structure (exceeding a degree) in 40 X-ray sources in clusters of galaxies. Significant evidence for extension is found only in the relatively nearby Perseus and Virgo clusters. For the remainder of the sources the results place stringent limits on the flux in any very large component.