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  • ASTRONOMY  (35)
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  • 1
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    The MIT spectroscopy investigations on AXAF and the study of supernova remnants (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The MIT High Resolution X-Ray Spectroscopy experiment on the AXAF, which will study physical conditions in celestial sources by means of detailed measurements of emission and absorption features in their spectra, involves two complementary dispersive instruments: Bragg Crystal Spectrometer (BCS) and High Energy Transmission Grating (HETG). This paper discusses the principles of operation of BCS and HETG and the results that will be obtained by these instruments. Measurements of individual line strengths obtained by the AXAF spectrometers will allow the application of plasma diagnostic techniques to a study of the detailed physical conditions in celestial objects, particularly in the optically thin plasma of supernova remnants, which is particularly well suited to the application of plasma diagnostics.
    Keywords: ASTRONOMY
    Type: Astrophysical Letters and Communications (ISSN 0888-6512); 26; 1-2,
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  • 2
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    Search for X-ray emission from Nova Cygni 1975 (1976)
    In:  Other Sources
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    Publication Date: 2011-08-16
    Description: A search for X-rays from Nova Cygni 1975 was carried out before, during, and after the time of optical maximum. No X-rays were detected over the spectral range 0.1-50 keV. On the basis of these results a strong upper limit of .0001 has been placed on the ratio of X-ray to optical luminosity for this nova, consistent with effective temperatures of about 10,000 K. If Nova Cygni 1975 is a virgin nova, its low mass exchange rate would imply that any associated X-ray emission would not be detectable by present techniques.
    Keywords: ASTRONOMY
    Type: Nature; 261; May 20
    Format: text
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  • 3
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    High-energy X-ray observations of Vela X-1 (1983)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Results are presented of observations of Vela X-1 in the 13-180 keV spectral range made with the A-4 instrument on board the HEAO 1 satellite. It is shown that the pulse period, measured during May-December 1978, is consistent with the long-term trend observed between 1975 and 1979. No evidence is detected for gross changes in the shape of the Vela X-1 pulse shape between May 1978 and December 1978, although some details of the 13-20 keV pulse profile seem to have varied during this period. The shape of the pulse profile is found to vary with energy between 13 keV and 70 keV. Pulse-phase-resolved spectroscopy is presented for Vela X-1 in this energy range. In addition, it is found that high energy (13-80 keV) light curves, obtained during each of three 50 day periods in 1977 and 1978, are quite similar to long-term light curves observed at lower energies.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal; vol. 266
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  • 4
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    X-ray bursters and the X-ray sources of the galactic bulge (1981)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: An attempt is made to distill from observational and theoretical information on the galactic bulge X-ray sources in general, and on the X-ray burst sources in particular, those aspects which seem to have the greatest relevance to the understanding of these sources. Galactic bulge sources appear to be collapsed objects of roughly solar mass, in most cases neutron stars, which are accreting matter from low-mass stellar companions. Type I bursts seem to result from thermonuclear flashes in the surface layers of some of these neutron stars, while the type II bursts from the Rapid Burster are almost certainly due to an instability in the accretion flow onto a neutron star. It is concluded that the studies cited offer a new and powerful observational handle on the fundamental properties of neutron stars and of the interacting binary systems in which they are often contained.
    Keywords: ASTRONOMY
    Type: Space Science Reviews; 28; 1, 19; 1981
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  • 5
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    Discovery of a 30.5 day periodicity in LMC X-4 (1981)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Keywords: ASTRONOMY
    Type: Astrophysical Journal; vol. 246
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  • 6
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    The hard X-ray spectrum of X Persei (1981)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Results of observations of 3U 0352 + 30, the source associated with the X Persei system, in the energy range 12-180 keV are reported. The measurements were made on 1978 August 22 with the UCSD/MIT High-Energy X-ray and Low-Energy Gamma-ray Experiment on HEAO 1. Data taken simultaneously in the energy range 2-50 keV indicate that, in addition to a 7 keV thermal bremsstrahlung component, there is a second component of higher energy. It is found that this higher energy component fits a power law of photon index 1.3 (+0.4, -0.5) and is pulsed at the 13.95 minute period of the lower energy component.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal; vol. 247
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  • 7
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    High energy X-ray observations of the 38-second pulsar (1981)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The results of observations of the 38-second pulsar obtained at high X-ray energies (13-180 keV) with the UCSD/MIT instrument aboard HEAO 1 are reported. The results include a measurement of the source location, measurement of the pulse profile, and determination of the average intensity and spectrum during each of three time intervals spanning a baseline of 1 year. The total intensity of the pulsar is seen to vary on a 6-month time scale. The spectrum is hard but, like other X-ray pulsars, steepens at energies above 20 keV.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal; vol. 246
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  • 8
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    HEAO 1 observations of the Perseus cluster above 10 keV (1981)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Results are presented of HEAO 1 observations of the Perseus cluster from 10 to 150 keV in 1977 August and 1978 February and August. The spectrum exhibits a previously unknown hard (greater than 25 keV) component in addition to the previously known thermal bremsstrahlung emission. The data presented show no significant evidence of variability from 10.5 keV to 93.5 keV, and a comparison of our results with earlier results indicates no strong evidence for variability above 25 keV over a time scale of 4 yr. If the hard-component excess is due to NGC 1275, the data imply a 2-6 keV X-ray luminosity of 1 x 10 to the 44th ergs/s for the galaxy, or about 15% of the total cluster emission from 2 to 6 keV and a 25-40 keV luminosity of 8 x 10 to the 43rd ergs/s.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal; vol. 243
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  • 9
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    SAS 3 observations of GX 1 + 4 (1981)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: GX 1 + 4 is one of the brightest celestial sources of high-energy X-rays. It is a pulsar with a period of approximately 2 min (perhaps a multiple of 2 min), decreasing at a variable rate which, since 1971, has averaged approximately 2% per year, but which can be larger than 5% per year. This is the largest rate of decrease observed for any pulsar. The rate of decrease appears to be correlated with the luminosity, in support of the idea that the period decrease is produced by accretion torques acting upon a neutron star. No evidence is seen for a Doppler shift due to motion of the pulsar in a binary orbit; this is consistent with the results of optical observations which suggest that any orbital period is fairly long (months to years). The spectrum of GX 1 + 4 is measured as a function of pulse phase, as well as the phase-averaged total spectrum, and the average spectrum of the pulses alone. The shape of the average pulsed spectrum suggests that the pulsations may be produced by 'hot spots' which are a few hundred meters in extent, with temperatures of approximately 10 to the 8th K (kT being approximately equal to 8 keV).
    Keywords: ASTRONOMY
    Type: Astrophysical Journal; vol. 243
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  • 10
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    X-ray bursters and the X-ray sources of the galactic bulge (1980)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Type 1 X-ray bursts, optical, infrared, and radio properties of the galactic bulge sources, are discussed. It was proven that these burst sources are neutron stars in low mass, close binary stellar systems. Several burst sources are found in globular clusters with high central densities. Optical type 1 X-ray bursts were observed from three sources. Type 2 X-ray bursts, observed from the Rapid Burster, are due to an accretion instability which converts gravitational potential energy into heat and radiation, which makes them of a fundamentally different nature from Type 1 bursts.
    Keywords: ASTRONOMY
    Type: NASA-CR-164240 , CSR-HEA-80-8
    Format: application/pdf
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