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  • 1
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    An upper limit to the low-energy X-ray flux from beta Persei (1975)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: A region of the sky including the binary system Algol (beta Persei) was observed with a one-dimensional, grazing-incidence X-ray telescope sensitive in the energy range from 0.5 to 4.0 keV. No statistically significant flux was detected above that attributable to the diffuse and cosmic-ray induced backgrounds. This result allows an upper limit of .02 billionths of an erg/sq cm sec keV at 1.6 keV to be set for the X-ray emission from this source at the epoch of observation. The absence of detectable low-energy X-rays is consistent with a thermal radio source, on condition that no flares occurred at the time of observation.
    Keywords: ASTRONOMY
    Type: Astrophysical Letters; 16; 1975
    Format: text
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  • 2
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    Detection of X-ray polarization of the Crab Nebula. (1972)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: Two different types of X-ray polarimeters were used in a sounding rocket to search for X-ray polarization of the Crab Nebula. Polarization was detected at a statistical confidence level of 99.7%. If the X-ray polarization is assumed to be independent of energy, the results of this and a previous experiment lead to a polarization of 15.4 (plus or minus 5.2) percent at a position angle of 156 (plus or minus 10) deg. This result confirms the synchrotron model for X-ray emission from the Crab Nebula.
    Keywords: SPACE SCIENCES
    Type: Astrophysical Journal; 174; May 15
    Format: text
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  • 3
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    The X-ray polarization experiment on the OSO-8 (1976)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The OSO-8 satellite, launched on June 21, 1975 contains two X-ray polarimeters. These polarimeters use mosaic crystals of graphite to yield polarization-sensitive Bragg reflection of stellar X-rays. The crystals reflect a narrow energy bandwidth centered at 2.6 and 5.2 keV. The polarimeter background signal is minimized by mounting the crystals on parabolic surfaces which focus the diffracted X-rays onto small-area, beryllium-window proportional counters. This technique permits the observation of low-intensity X-ray sources and reduces the possibility of systematic background effects which could lead to a false signature of polarization. A description of the instrument is given, and the sensitivity to polarization, particularly in regard to binary sources, is discussed. Preliminary results for Cen X-3 and GX5-1 are presented.
    Keywords: ASTRONOMY
    Type: CONTRIB-118 , NASA. Goddard Space Flight Center X-ray Binaries; p 81-96
    Format: text
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  • 4
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    One-dimensional focusing X-ray telescope for stellar X-ray astronomy (1975)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: A one-dimensional X-ray telescope of the Kirkpatrick-Baez design is described. The instrument consists of a grazing-incidence X-ray telescope and a multiwire proportional counter. The optics were provided with a gold reflecting surface to yield an energy response from below 0.25 to above 4.0 keV. The angular resolution of the system is 6 min by 9.5 deg over a 1.1 deg by 9.5 deg field of view.
    Keywords: ASTRONOMY
    Type: Review of Scientific Instruments; 46; Aug. 197
    Format: text
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  • 5
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    An upper limit to the low-energy X-ray flux from Beta Persei (1975)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: A region of the sky including the binary system Algol (Beta Persei) was observed with a one-dimensional grazing-incidence X-ray telescope sensitive in the energy range from 0.5 to 4.0 keV. No statistically significant flux was detected above that attributable to the diffuse and cosmic-ray induced backgrounds. This result allows an upper limit of 2 by 10 to the -11th power ergs/sq cm/sec/keV at 1.6 keV to be placed on the X-ray emission from this source at the epoch of observations. It is concluded that the absence of detectable low-energy X-rays is consistent with a thermal radio source, provided that no flares occurred at the time of observation.
    Keywords: ASTRONOMY
    Type: Astrophysical Letters; 16; 4, 19; 1975
    Format: text
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  • 6
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    New observations of pulsed X-ray emission from NP 0532 (1976)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: Large-area proportional counters sensitive from 0.6 to 23 keV were used to observe about 3 min of pulsed X-ray emission from NP 0532 during two lunar-occultation experiments. A detailed pulse profile with 65-microsec resolution shows that the X-ray primary-pulse shape is essentially identical to its optical counterpart. Spectral data on the pulsed X-ray emission are presented. A pulse-by-pulse examination of the data shows no evidence for temporal variability.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal; 203; Jan. 15
    Format: text
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  • 7
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    Search for thermal X-ray line emission from the Crab Nebula (1977)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: Observations of the Crab Nebula from 1.85 to 8 keV obtained with the large-area graphite crystal spectrometer on OSO-8 show a smooth featureless continuum with an absence of X-ray emission lines from highly ionized Si and S. Upper limits on the line emission are used to derive an upper limit to the emission measure for a thermal source associated with the Crab Nebula. Existing evidence for an extended thermal source is discussed, and it is shown that the evidence is not contradicted by the upper limits set with the spectrometer data.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal; vol. 216
    Format: text
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  • 8
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    A soft X-ray map of the Perseus cluster of galaxies (1976)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: A 0.5-3-keV X-ray map of the Perseus cluster of galaxies is presented. The map shows a region of strong emission centered near NGC 1275 plus a highly elongated emission region which lies along the line of bright galaxies that dominates the core of the cluster. The data are compared with various models that include point and diffuse sources. One model which adequately represents the data is the superposition of a point source at NGC 1275 and an isothermal ellipsoid resulting from the bremsstrahlung emission of cluster gas. The ellipsoid has a major core radius of 20.5 arcmin and a minor core radius of 5.5 arcmin, consistent with the values obtained from galaxy counts. All acceptable models provide evidence for a compact source (less than 3 arcmin FWHM) at NGC 1275 containing about 25% of the total emission. Since the diffuse X-ray and radio components have radically different morphologies, it is unlikely that the emissions arise from a common source, as proposed in inverse-Compton models.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal; 209; Nov. 1
    Format: text
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  • 9
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    Search for X-ray polarization in the Crab pulsar (1978)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: Results of a search for X-ray polarization in the Crab pulsar are presented which were obtained by observing the pulsar at 2.6 and 5.2 keV with identical X-ray polarimeters aboard OSO 8. The polarization in different portions of the X-ray light curve is analyzed, the polarization contribution due to the nebula is removed, and the results of the analysis are given for isolated portions of both the primary pulse and the interpulse at 2.6 and 5.2 keV. No evidence for X-ray polarization is found at the 99% confidence level; 3-sigma upper limits to the polarization at 2.6 keV are given along with the largest polarization allowed at 5.2 keV by the 99% confidence counter. It is noted that the trailing edge of the interpulse at 2.6 keV is 26% polarized at the 92% confidence level, while the 5.2-keV polarization measurement of 40% in the leading edge of the primary pulse is different from zero at 96% confidence. X-ray and optical polarization measurements are compared.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal; vol. 225
    Format: text
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  • 10
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    Upper limit of the X-ray polarization of the Crab Nebula (1971)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Taurus X-1 X ray emission polarization from rocket-borne polarimeter measurements, utilizing incoherent scattering
    Keywords: SPACE SCIENCES
    Type: CRAB NEBULA SYMPOSIUM; Aug 05, 1970 - Aug 07, 1970; MANCHESTE; United Kingdom
    Format: text
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