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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Space science reviews 40 (1985), S. 339-345 
    ISSN: 1572-9672
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Her X-1 has been observed with EXOSAT for one 35d cycle between March 1 and April 5, 1984 at about 4 day intervals. During three observations, absorption dips were encountered showing fluctuations with time scales in the several hundred seconds range. The data are interpreted with a model where random superposition of absorbing blobs or inhomogeneous structures within the accretion disk, in the line of sight, cause these intensity variations. The calculations give a measure of the extent of the disk both in vertical and radial directions.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Space science reviews 40 (1985), S. 347-353 
    ISSN: 1572-9672
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Sampling observations of a complete 35d cycle of Her X-1 during 1 March to 5 April 1984 with the low and medium energy X-ray detectors of EXOSAT are presented. The intensities measured in the Argon detectors are compared with the UHURU 35d light curve to obtain the turn-on times of two consecutive cycles as JD 2445753.0 ± 1.0, and JD 2445788.0 ± 0.5. The low energy data is used to determine the rotation period and its derivative as: 1.23779200 s ± 50 ns, and (-2 ± 1) × 10-13 respectively, at the epoch JD 2445778.56. Analysis of the pulse arrival phases indicate that during mid-on phase of the 35d cycle there is shift of about 180°. Evidence for the long term correlated changes of P35 and P1.24s is presented, confirming the low quality of the 35d clock and suggesting that the basic clock mechanism must lie in the disk structure itself.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Space science reviews 40 (1985), S. 527-529 
    ISSN: 1572-9672
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Conclusion The EXOSAT observation of PSR 1055-52 supports strongly the idea of a thermally radiating neutron star, either still cooling from its initially high temperature or reheated by unpinning of vortex lines in its superfluid interior. The data do not confirm the Cheng & Helfand conclusions about a synchrotron nebula with a power law spectrum. The discrepancy in the data is, nevertheless, only a ≈ 3.5 σ effect, as no ME data could be used to get a firm upper limit of the flux above ≈ 1 keV. With regard to the outstanding theoretical interest in the structure of neutron stars we hope for further observations to clarify this question.
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Space science reviews 40 (1985), S. 156-156 
    ISSN: 1572-9672
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The detection of X-rays from Nova Muscae 1983 (discovered on January 18, 1983) constitutes the first detection of X-rays from a classical nova during outburst. X-ray observations were carried out on 1984 April 20 and July 14 when Nova Mus had entered the nebular stage. During both observations no significant flux was observed with the medium energy detectors (2–50 keV). The source was detected with the low energy detector (.04–2 keV) using 3000 Å Lexan and Parlene- N-Aluminium filters; counting rates of (3.4 ± 1.2) × 103 and (3.7 ± 1.2 × 10-3 counts/sec were measured with the respective filters. The source was detected again on July 14 with about the same intensity. Either a shocked shell of circumstellar gas emitting 107 thermal bremsstrahlung at 1035 erg/sec intensity or a white dwarf remnant emitting 3.5 × 105 blackbody radiation at 1037 erg/sec luminosity are compatible with the measurements. Spectra taken in the visual spectral range show strong forbidden coronal emission lines of [FeVII] λ6085, [FeX] λ6374, and as never observed before in such a strength, [FeXIV] λ5303 requiring excitation temperatures of ∼ 2 × 106 °K.
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Space science reviews 40 (1985), S. 355-360 
    ISSN: 1572-9672
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In March/April 1984 eleven EXOSAT observations of Her X-1 were performed sampling a full 35 day cycle. Spectral analysis of the ME and GSPC data shows that the iron line emission is present during all phases. During the main-on state we see an iron line at 6.65 ± 0.07 keV with a FWHM of 1–2 keV and an equivalent width of 300 to 400 eV. The high resolution GSPC data indicate that the line profiles have external wings and are not simple Gaussian. We report for the first time on the detection of an iron line during the intermediate-on state with about the same parameters as the main-on state line but an equivalent width a factor of 2 larger. During the off state between main-on and intermediate-on we detected a broad iron line feature at about 6.0 keV with an equivalent width of 2 keV. We discuss the Alfven region and a hot corona at the inner region of the accretion disk as the possible sites of the line production.
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Astrophysics and space science 130 (1987), S. 279-279 
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The initial discovery of soft X-rays from Nova Muscae 1983 was followed by eight additional observations of the three brightest novae whose outburst stage coincided with the lifetime ofEXOSAT satellite; namely three more observations of Nova Muscae 1983, three observations of Nova Vulpeculae 1984#1 (PW Vul), and two observations of Nova Vulpeculae 1984#2. Through these observations we sampled the soft X-ray light curve of classical novae from optical maximum to ∼900 days after. The observations seem best explained by the constant bolometric luminosity model of a hot white dwarf remnant. Although the measurements suffer from limited statistics, very broad energy bandpass, and incomplete sampling of any single nova, their constraints on the theories of nova outburst are significant. One constraint is that the lifetime of the white dwarf remnant in Nova Muscae 1983 is ∼2 to 3 years, which leads to the conclusion that the burned envelope massM burn should be of the order of $$10^{ - 6} \left( {\frac{{10^{38} erg s ^{ - 1} }}{{L_{burn} }}} \right)M_ \odot $$ . The second constraint is that the maximum temperature, of the white dwarf remnant should approximately be within 200 000 K to 400 000 K. We estimate that a white dwarf remnant evolving like the central star of a planetary nebula, with core mass of 0.8 to 0.9M ⊙, core luminosity of ∼2×104 L ⊙, and envelope mass of 10−6 M ⊙, can explain the general characteristics of the X-ray measurements for Nova Muscae 1983. In order to have ≥1.1M ⊙ core mass, estimated from the early observations of bolometric luminosity in the UV to infrared range, a wind withM≤5×10−7 M ⊙ yr−1 appears to be necessary. The few observations of Nova Vulpeculae 1984 #1 and Nova Vulpeculae 1984#2, during the first year after outburst, give a risetime and intensity that is consistent with a constant bolometric luminosity model.
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