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  • 1
    Electronic Resource
    Electronic Resource
    A new AM Her-like X-ray source (1983)
    [s.l.] : Nature Publishing Group
    Nature 301 (1983), S. 318-321 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The X-ray observations were carried out with the low energy detector l (LED1) of the HEAO A-2 experiment13 and the Imaging Proportional Counter (IPC) on the Einstein Observatory . From superposed scans of LED1 for the days 15-23 November 1977 a new X-ray source, now designated H0139-68, was ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/301318a0
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  • 2
    Electronic Resource
    Electronic Resource
    Rapid Variations in the High Energy X-ray Flux from Cyg X-1 (1971)
    [s.l.] : Nature Publishing Group
    Nature 232 (1971), S. 38-40 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The X-ray telescope was similar to that flown by us1 before, and comprised an Nal(Tl) crystal of effective area 97 cm2 provided with active and passive collimators and having an FWHM of 18.6°. The telescope was mounted on an orienting device with its axis at an angle of 17° with respect to ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/232038a0
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  • 3
    Electronic Resource
    Electronic Resource
    Further simultaneous hard X-ray and optical observations of Sco X-1 (1974)
    [s.l.] : Nature Publishing Group
    Nature 250 (1974), S. 38-40 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] In our 1971 observations we found a positive correlation between the optical luminosity and the intensity of hard X rays at the optically enhanced phase of Sco X-l (refs 2 and 3). Although the optical enhancement seemed to be a flare, a rather poor time resolution of the photographic observation ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/250038a0
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  • 4
    Electronic Resource
    Electronic Resource
    Sudden Changes in the Intensity of High Energy X-Rays from Sco X -1 (1969)
    [s.l.] : Nature Publishing Group
    Nature 224 (1969), S. 51-53 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Table 1 summarizes the experimental observations. The excess counts due to Sco X-l were obtained by subtracting the counting rates corresponding to the north direction which did not include any known X-ray sources. The atmospheric attenuation was taken into account from the thickness of the ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/224051a0
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  • 5
    Electronic Resource
    Electronic Resource
    Observation of soft X-ray emission from a region near Per X-1 (1974)
    Springer
    Astrophysics and space science 28 (1974), S. 185-191 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Soft X-ray emission from the X-ray source Per X-1 was observed in the 0.4–2 keV energy interval from a rocket borne X-ray detector. Spectral analysis of the data indicates that in the 0.4–2 keV band the X-ray emission from Per X-1 can be fitted either with a power law of slope-(4.8±1.2) or a thermal bremsstrahlung spectrum with akT value of (0.26 −0.08 +0.12 ) keV. Such a steep spectrum is inconsistent with the spectrum measured above 2 keV. The measured flux in 0.4–2 keV band corresponds to X-ray luminosity of 3×1045 ergs s−1 for Per X-1.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00642248
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  • 6
    Electronic Resource
    Electronic Resource
    X-Ray emission from the pleiades cluster (1983)
    Springer
    Astrophysics and space science 92 (1983), S. 177-180 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Detection of a new X-ray source and its identification with the Pleiades cluster is reported here. The new X-ray source has an X-ray luminosity of ∼1032 ergs s−1 in the 0.15–3.0 keV energy band. The observed X-ray emission could be explained as integrated emission from a large number of stars in the cluster.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00653598
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  • 7
    Electronic Resource
    Electronic Resource
    The spectrum of diffuse cosmic X-rays in the 20–125 keV range (1972)
    Springer
    Astrophysics and space science 15 (1972), S. 272-283 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Diffuse cosmic X-rays in the energy range 20–125 keV were measured in four balloon flights from Hyderabad, India during 1968–70 using almost identical X-ray telescopes mounted on oriented platforms. The results from these flights show that the spectrum of the diffuse cosmic X-rays can be represented by the form dN/dE=29E −2.1±0.3 photons/(cm2 sr s keV) in 20–125 keV interval after corrections for photoelectric absorption and Compton scattering effects in the atmosphere. The best fit spectrum of all published results in the energy interval 20–200 keV can be represented by the form dN/dE=36E −2.1±0.1 photons/(cm2 sr s keV) after similar corrections are effected, and there is no need for a change of spectral index in this energy interval. The intensity at 20 keV obtained from the above spectrum agrees well with that given by the spectral form dN/dE=10E −1.7±0.1 photons/(cm2 sr s keV) in the energy interval 1–20 keV in several rocket experiments. Therefore it is concluded that if there is a break in the spectrum, it occurs between 10 and 20 keV with a change of spectral index by about 0.5, or the index is continuously changing from 1.7±0.1 to 2.1±0.1 in 10–20 keV interval. The implications of the results are briefly discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00649921
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  • 8
    Electronic Resource
    Electronic Resource
    The flattening of the X-ray spectrum of sco X-1 at energies beyond 40 keV (1971)
    Springer
    Astrophysics and space science 10 (1971), S. 500-507 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The measurements of the hard X-ray spectrum of Sco X-1 in the energy interval 20–150 keV in three balloon flights from Hyderabad, India are reported. These results show conclusively that the spectrum of Sco X-1 is very flat in the energy interval 40–150 keV and the measured fluxes beyond 60 keV are several orders of magnitude higher than those expected on the basis of an extrapolation of bremsstrahlung spectrum from a thin hot plasma at a temperature corresponding tokT=5 keV, which is applicable for Sco X-1 for energies 〈40 keV. The results are compared with those of other investigators of hard X-rays from Sco X-1, and the implication of the results is briefly discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00649692
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  • 9
    Electronic Resource
    Electronic Resource
    X-rays from supernovae remants 3C 400.2 (≡ G53.7-2.2) and MSH 15-56 (1983)
    Springer
    Astrophysics and space science 89 (1983), S. 279-283 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Detection of two new soft X-ray sources and their identification with the supernova remnants (RNRs) 3C400.2 and MSH 15-56, is reported. From the observed X-ray flux in the 0.7–2.0 keV energy range, the X-ray luminosity of 3C400.2 is derived to be in the range of (2.7–5.3)×1035 ergs s−1 and that of MSH 15-56 in the range of (0.9–1.6)×1035 ergs s−1. If we use the standard adiabatic shockwave model for the SNR's, an age of ∼(1.4–3.2)×104 yr is derived for 3C400.2 whereas MSH 15-56 is found to be younger of an age of (5–10)×103 yr.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00655980
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  • 10
    Electronic Resource
    Electronic Resource
    Energy spectrum and time variations of hard X-rays from Cyg X-1 (1972)
    Springer
    Astrophysics and space science 18 (1972), S. 408-424 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Experimental results on the intensity, energy spectrum and time variations in hard X-ray emission from Cyg X-1 based on a balloon observation made on 1971, April 6 from Hyderabad (India) are described. The average energy spectrum of Cyg X-1 in the 22–154 keV interval on 1971 April 6 is best represented by a power law dN/dE=(5.41±1.53)E −(1.92±0.10) photons cm−2s−1 keV−1 which is in very good agreement with the spectrum of Cyg X-1 derived from an earlier observation made by us on 1969 April 16 in the 25–151 keV band and given by dN/dE=(3.54±2.44)E −(1.89±0.22) photons cm−2s−1 keV−1. A thermal bremsstrahlung spectrum fails to give a good fit over the entire energy range for both the observations. Comparison with the observations of other investigators shows that almost all balloon experiments consistently give a spectrum of ∼E −2, while below 20 keV the spectrum varies fromE −1.7 toE −5. There is some indication of a break in the Cyg X-1 spectrum around 20 keV. Spectral analysis of data in different time intervals for the 1971 April 6 flight demonstrates that while the source intensity varies over time scales of a few minutes, there is no appreciable variation in the spectral slope. Analysis of various hard X-ray observations for long term variations shows that over a period of about a week the intensity of Cyg X-1 varies upto a factor of four. The binary model proposed by Dolan is examined and the difficulties in explaining the observed features of Cyg X-1 by this model are pointed out.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00645405
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