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  • ASTROPHYSICS  (4)
  • 1
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    On the origin of the diffuse x ray background (1991)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The first measurement is reported of the intensity and spectrum of the diffuse x ray background in the 0.16 to 3.5 keV band which is free from contamination by sources with fluxes greater than approx. 6 x 10(exp -14) erg/sq cm/s. This result was made possible by the development of a number of techniques for reducing cosmic ray contamination and instrumental artifacts in the data collected by the Einstein Observatory imaging proportional counter. The analysis of the background data reveals a mean absolute intensity for the emission I sub x(0.16 to 3.5 keV) approx. = 5.6 x 10(exp -8) erg/sq cm/s/sr. The intensity is dependent on galactic longitude even when only high galactic data are used, allowing the setting of a lower limit of 20 pct. on the galactic contribution to the mean emission band. The spectrum of the total background is consistent with a power law of slope similar to 0.7 between 0.16 and 3.5 keV with evidence for a steep rise toward lower energies. Preliminary evidence is also reported for the association of faint radio sources with peaks in the arcminute scale fluctuations of the diffuse x ray surface brightness distribution and then some implications are considered of these results.
    Keywords: ASTROPHYSICS
    Type: NAS-NRC, High-Energy Astrophysics. American and Soviet Perspectives; p 174-191
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    NASA TECHNICAL REPORTS
  • 2
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    The progenitors and products of supernovae (1987)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Much of the recent radio and X-ray observational work relevant to the questions of the progenitor populations and explosion products of supernovae is reviewed. Several illustrative examples are given of how X-ray data on shell-type supernova remnants, coupled with analytic and numerical hydrodynamic models, can constrain the mass and evolutionary state of the stellar precursor. The population of Crab-like remnants is examined, pointing out the restrictions imposed on explosion models by the statistics of collapsed remnant cores.
    Keywords: ASTROPHYSICS
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    NASA TECHNICAL REPORTS
  • 3
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    The prevalence of supernova remnants among unidentified Galactic radio sources (1989)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Nine Galactic radio sources were mapped to identify new Crab-like and composite supernova remnants. The sources were selected on the basis of existing stringent upper limits on their hydrogen recombination line fluxes. One new Cracb-like remnant, one new composite remnant, at least one, and probably two, new shell-like remnants, and a compact H II region were found, along with the expected collection of extragalactic objects. The results suggest that there are several hundred SNRs in the Galaxy which are detectable with current instruments, but which have yet to be identified.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 341; 151-162
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    NASA TECHNICAL REPORTS
  • 4
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    The discovery of an X-ray selected, radio-loud quasar at z = 3.9 (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-08-27
    Description: About 600 weak X-ray sources from a data base of about 100,000 2-4sigma fluctuations derived from Einstein Observatory imaging proportional counter X-ray images are selected on the basis of a flux-limited catalog of radio sources in the northern sky. Optical spectroscopy of only six of these sources resulted in the discovery of a quasar with an emission-line redshift of 3.87. Subsequent VLA observations reveal the source to have a flat-spectrum radio core plus an unresolved radio lobe 2.5 arcsec away with a spectral index of 1.45. The lobe is connected to the core by a weak jet. The integrated flux density of the source at 20 cm is 0.66 Jy. The v magnitude of the quasar is 19.5, and the tentative X-ray sources has a very soft spectrum. The properties of this object are discussed in the context of known high-redshift radio sources and existing X-ray selected quasar samples, and the potential of the present discovery technique for examining the properties of very distant active galaxies is explored.
    Keywords: ASTROPHYSICS
    Type: Astronomical Journal (ISSN 0004-6256); 104; 2 Au
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