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  • 1
    Electronic Resource
    Electronic Resource
    Hubble space telescope observations of AGN's in the ultraviolet: BL Lac and Q2345+007 (1996)
    Springer
    Astrophysics and space science 240 (1996), S. 295-303 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We report the first polarimetric observations in the ultraviolet of two AGN's, the blazar BL Lac and the gravitational lens candidate Q2345+007. We find strong (p〉3%) and variable UV polarization in BL Lac, two of the characteristics exhibited by blazars in the visible. The polarization of BL Lac in the UV decreased significantly (from 18% to 〈5%) over a timescale of days. The flux density in the polarimetric bandpass showed changes which were not correlated with the polarimetric changes. The behavior of BL Lac in the UV is consistent with the two-component model of its polarized flux proposed by Brindleet al. (1985). The UV properties of the images in the Q2345+007 system are consistent with a gravitational lens interpretation. The QSO imaged in Q2345+007A is an excellent candidate to monitor for variable polarization on a timescale of weeks. Detecting the same polarimetric variation in each image of a gravitational lens may be the most effective method of determining the time-of-flight difference between the two image paths.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00639593
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  • 2
    Electronic Resource
    Electronic Resource
    The optical polarization of X-ray binaries (1977)
    Springer
    Astrophysics and space science 52 (1977), S. 201-211 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Polarimetric observations of close binaries may reveal the presence of a black-hole secondary. The Einstein photometric effect will introduce a characteristic, time-varying signature upon the interstellar polarization. For several reasons, it is concluded that the short time-scale variability in the polarization in HDE 226868 is caused by Rayleigh scattering from gas streams known to exist in the system. X Persei may have a variable polarization consistent with the predicted effect.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00647164
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    The variable X-ray spectrum of Cyg XR-1 (1970)
    Springer
    Space science reviews 10 (1970), S. 830-868 
    Details
    ISSN: 1572-9672
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The variability of the X-ray spectrum of the discrete source Cyg XR-1 (α = 19h 56m δ = +35°.1) is reviewed. The variations observed in the energy region accessible to balloon borne detectors (energies greater than 20 keV) can be explained by assuming them to be caused by the eclipsing properties of a binary system. It is suggested that the system is composed of a source of small angular extent having a spectrum similar to that of a black body at approximately 1.5 × 108 K (kT= 12.5 keV) and a non X-radiating companion which eclipses it at intervals of 2.9850 days. The system would be surrounded by an X-radiating plasma whose photon flux between 1 and 100 keV can be approximated by a power law spectrum whose exponent is — 1.7.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00167340
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  • 4
    Electronic Resource
    Electronic Resource
    Placing faith in the masses? (1992)
    [s.l.] : Nature Publishing Group
    Nature 355 (1992), S. 589-590 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] BECAUSE black holes require both quantum mechanics and general relativity to describe them completely, a reliably identified black hole would provide physicists with a useful testbed on which to verify and refine attempts to unify the two theories. Computed evolutionary tracks of ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/355589a0
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  • 5
    Electronic Resource
    Electronic Resource
    Eclipsing Binary Model of Cygnus XR-1 (1971)
    [s.l.] : Nature Publishing Group
    Nature 233 (1971), S. 109-110 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Agrawal et al. observed the source in nineteen consecutive periods of approximately 5 min from 0002 to 0315 UT, on April 6, 1971. The mean count rate in the 22.5-99 keV energy range for periods 1 to 12 was 260 counts per min (although non- random variations in the count rate appear to be present) ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/233109a0
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  • 6
    Electronic Resource
    Electronic Resource
    The direct reduction of astronomical x-ray spectra (1972)
    Springer
    Astrophysics and space science 17 (1972), S. 472-481 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A matrix method is outlined for the reduction of astronomical X-ray spectral data which includes the effects of detector resolution and fluorescent escape phenomena. The differences between this method and the ‘backward reduction’ or multiple grid methods presently employed are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00642917
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  • 7
    Electronic Resource
    Electronic Resource
    A balloon-borne observation of the X-ray source Cygnus XR-1 (1972)
    Springer
    Astrophysics and space science 17 (1972), S. 482-488 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract An observation of the variable X-ray source Cygnus XR-1 was made with a balloon-borne proportional counter in the energy region 22–70 keV. The resultant spectrum indicates that the source was in a state of maximum flux during the time period 1915–2005 UT, 15 January, 1968.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00642918
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    Paper (German National Licenses)
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  • 8
    Electronic Resource
    Electronic Resource
    The signature of a black hole transit (1989)
    Springer
    Astrophysics and space science 155 (1989), S. 3-11 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A black hole transiting a companion star in a binary system will produce a time-varying intensity profile as observed at the Earth because of the Einstein photometric effect (gravitational lens phenomenon). If the transited star is an early-type supergiant with electron scattering as its dominant atmospheric opacity source, then variable linear polarization will also result from the destruction of the circular symmetry of the observed stellar disk. The simultaneous variation of the three Stokes parametersI, Q, andU may be thought of as the signature of a black hole transit. Monte-Carlo calculations show that the effect has the properties expected from qualitative considerations. The amplitude of the photometric and polarimetric light curves in a typical X-ray binary is too small to be observed with present instrumentation. A black hole transit might be detectable in a binary having a large separation of the components. The signature is also masked in close binaries by the much larger variability caused by the changing aspect of the tidally distorted OB star. The polarization induced by tidal distortion always produces a derived inclination of 90° when the standard method of analyzing the data is used. This effect may contribute to the unrealistically large values of inclination derived from polarimetric observations for the Cyg XR-1/HDE226868 system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00645201
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  • 9
    Electronic Resource
    Electronic Resource
    The polarization of celestial X-rays (1967)
    Springer
    Space science reviews 6 (1967), S. 579-600 
    Details
    ISSN: 1572-9672
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The processes by which X-radiation may be emitted by celestial sources are investigated, and the net polarization such radiation would possess is predicted. The amount of polarization observed at the Earth would depend both on the mechanism producing the radiation and on the fractional extent of the source over which it is coherently polarized. Highly polarized X-radiation would suggest synchrotron emission as the source mechanism. Radiation whose polarization is low but nonzero would be produced by synchrotron emission from a source whose magnetic fields are inhomogeneous on a large scale, or by bremsstrahlung of electrons whose velocity vectors lie in one predominant direction. Nonobservable polarization would result from sources of synchrotron radiation whose magnetic fields show small-scale irregularities, from the bremsstrahlung of electrons whose velocity vectors are either random or spherically symmetric in direction over the entire source, or from sources whose mechanism of producing the radiation imparts no net polarization, e.g., thermal radiation from neutron stars, line radiation from electronic shell transitions within atoms, and the inverse Compton effect. Measurement of the net polarization of the X-rays from the several known celestial sources could thus lead to the specification of the mechanisms capable of producing the radiation from such sources.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00168792
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