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  • 1
    Electronic Resource
    Electronic Resource
    An extended X-ray low state from Hercules X-1 (1985)
    [s.l.] : Nature Publishing Group
    Nature 313 (1985), S. 119-121 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Hercules X-1 (Her X-1) was observed by the European Space Agency's EXOSAT Observatory (see ref. 12 for additional details) on 1983 June 28, 37 days after the Tenma X-ray satellite observed that it was close to its maximum high-state intensity13. During the 35-day cycle, Her X-1 normally has a ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/313119a0
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  • 2
    Electronic Resource
    Electronic Resource
    Galactic X-ray sources (1979)
    [s.l.] : Nature Publishing Group
    Nature 281 (1979), S. 256-258 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] ASTRONOMERS are becoming increasingly aware that to understand X-ray sources better they must observe them over the entire electromagnetic spectrum. Participants at a recent multidisciplinary meeting* presented the results of observational and theoretical studies ranging from the radio to the ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/281256a0
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  • 3
    Electronic Resource
    Electronic Resource
    Detection Of Soft X-Ray Emission From Comet C/1995 O1 (Hale–Bopp) (1997)
    Springer
    Earth, moon and planets 77 (1997), S. 293-298 
    Details
    ISSN: 1573-0794
    Keywords: Comets ; general-comets ; individual (Hale–Bopp 1995 O1
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract We report the detection of soft X-rays from comet C/1995 O1 (Hale-Bopp) by the Low Energy Concentrator Spectrometer (LECS) on-board the X-ray satellite, BeppoSAX. The observations took place on 1996 September 10–11 approximately 1 day after a large dust outburst (Schulz et al., 1997–1999). After correcting for the comets motion, a 7σ enhancement was found centered (2.1 ± 1.3) x 105 km from the position of the nucleus, in the general solar direction. The total X-ray luminosity in the 0.1–2.0 keV energy band is 5 x 1016 erg s−1 which is at least a factor of ∼ 3 greater than measured by the Extreme Ultraviolet Explorer (EUVE)4 days later and suggests that the bulk of the emission measured by the LECS is related to the dust outburst. The extracted LECS spectrum is well fit by a thermal bremsstrahlung-like distribution of temperature of 0.29 ± 0.06 keV - consistent with that observed in other comets. We find no evidence for fluorescent carbon or oxygen emission and place 95% confidence limits of 1.0 x 1015 and 7.8 x 1015 erg s−1 to narrow line emission at 0.28 and 0.53 keV, respectively. We calculate that if such lines are present, they constitute at most 18% of the 0.1–2.0 keV continuum luminosity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006253028962
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  • 4
    Electronic Resource
    Electronic Resource
    The X-ray source A0538-66 in optical quiescence (1981)
    Springer
    Space science reviews 30 (1981), S. 433-439 
    Details
    ISSN: 1572-9672
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Photometric observations of A0538-66 in quiescence show that the optical star is an object of equivalent spectral type B7eII. Spectroscopic data taken simultaneously confirm this spectral classification and are consistent with the reported periodic variations seen in the emission lines. It is unlikely that the optical outburst is due to X-rays reprocessed in the atmosphere of the primary star or elsewhere.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01246060
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  • 5
    Electronic Resource
    Electronic Resource
    Optical observations of the X-ray source 2S0921-630 (1981)
    Springer
    Space science reviews 30 (1981), S. 279-286 
    Details
    ISSN: 1572-9672
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We report photometric observations of the optical counterpart of the X-ray source 2S0921-630. The data, obtained at the South African Astronomical Observatory during 3 weeks in 1980 and 1981, are consistent with a 17.9 day periodic modulation of the flux in the B band. Correlated variability of the (B-V) and (U-B) colour indices with the B mag. is demonstrated and quantified. The observed B mag. and colours at maximum and minimum light are used to compute some of the system parameters. A model of 2S0921-630 is proposed in terms of a binary system in which the variable inclination of a luminous accretion disc produces the long-term modulation of the optical flux.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01246032
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  • 6
    Electronic Resource
    Electronic Resource
    An investigation into the nature of the 4.4 hr periodic source 4U1755-33 (1985)
    Springer
    Space science reviews 40 (1985), S. 213-217 
    Details
    ISSN: 1572-9672
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We present the results of a continuous 18 hour observation of 4U1755-33 made with the European Space Agency's EXOSAT Observatory. Four 50 min dips in X-ray intensity were observed equally spaced with a period of 4.4 hrs, confirming the periodicity first suggested in White et al. (1984). The dips are spectrally independent. We examine the properties of 4U1755-33 and conclude that the source is most probably point-like and that the metallicity of the absorbing material is at least 600 times less than cosmic values.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00212887
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  • 7
    Electronic Resource
    Electronic Resource
    An EXOSAT observation of the morphology of the coronal X-ray emission from algol (1985)
    Springer
    Space science reviews 40 (1985), S. 25-33 
    Details
    ISSN: 1572-9672
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The X-ray emission from Algol is thought to originate in a corona associated with the K star in this system. We report the results of a 35 hr continuous EXOSAT observation through secondary optical eclipse that was designed to measure the structure of the corona. No obvious X-ray eclipse was seen. The spectrum measured by the ME gives a temperature of 2.5 × 107 K, consistent with the hard component previously seen by the Einstein SSS. The soft component previously reported by the SSS would only contribute at most 25% to the count rate seen in the LE (used with Al/P). The lack of a hard X-ray eclipse indicates the dimensions of the higher temperature emission region to be comparable to or greater than the size of the K star. An X-ray flare was detected with a peak luminosity of 1.4 × 1031 erg s-1 and a total duration of 8 hours. The peak temperature was 5.0 keV with an emission measure of 9.4 × 1053 cm-3. The thermal nature of the flare is confirmed by the detection of an iron line with an EW of ∼2 keV. By equating the observed decay time of the flare to a known cooling law gives a dimension for the flaring loop of ∼0.3 stellar radii. This is much smaller than the dimensions of the hard component inferred from the lack of an eclipse. It seems probable that the flare occurred in one of the loops responsible for the lower temperature component seen by the SSS.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00212862
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  • 8
    Electronic Resource
    Electronic Resource
    The spectral and temporal variability of the X-ray transient 4U1630-47 (1985)
    Springer
    Space science reviews 40 (1985), S. 391-398 
    Details
    ISSN: 1572-9672
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We present the results of four observations made by the European Space Agency's EXOSAT Observatory of the X-ray transient 4U1630-47 during its 1984 outburst. We observed marked spectral changes as the source decayed from a maximum observed intensity of 8×10−9 erg/cm2/sec (1.5–10 keV). The spectrum could be modelled by a soft ‘thermal-like’ component with a high energy power-law tail. The relative contribution of the soft to hard component decreased as the total luminosity decreased. We compare these changes with those observed from the black hole candidate Cyg X-1 when it transitions from a high to a low state. In addition we report the discovery of short timescale intensity variations (down to ∼ 50 msec) with a characteristic timescale of ∼ 20 sec. We present a precise position for this unidentified source.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00179847
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  • 9
    Electronic Resource
    Electronic Resource
    The discovery of a 25 min regular modulation in the X-ray flux from 2S0142+61 (1985)
    Springer
    Space science reviews 40 (1985), S. 157-162 
    Details
    ISSN: 1572-9672
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A 13 hr observation of 2S0142+61 on 1984 August 27 by EXOSAT shows the X-ray flux of 2S0142+61 to be modulated with a period of 1456+/-6 s. The 1–10 keV spectrum is two component with a ∼0.7 keV thermal and 0.0 energy index power law, with 30% of the total luminosity in the thermal component. The spectrum is absorbed by ∼1 × 1022 H cm-2. Only the hard component is pulsed with a 3 to 10 keV peak to mean amplitude of 35%. Below 2 keV the modulation is less than a few percent. The total 1–10 keV luminosity is 3.5 × 1032 erg s-1 for a distance of 100 pc. Possible optical counterparts are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00212881
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  • 10
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    Discovery of narrow X-ray absorption features from the low-mass X-ray binary X 1254-690 with XMM-Newton (2003)
    EDP Sciences
    Details
    Publication Date: 2003-09-01
    Print ISSN: 0004-6361
    Electronic ISSN: 1432-0746
    Topics: Physics
    Published by EDP Sciences
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