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  • 11
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    HEAO 1 observations of high-energy X-rays from 3C273 (1979)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: The first detection of high energy (13 to 120 keV) X rays from the quasar 3C273, made by the HEAO 1 satellite, is reported. Observations were made with the 13 to 180 keV slat collimated detectors of the high energy X-ray and low energy gamma-ray (A4) experiment during December 1977-January 1978 and June-July 1978. Results are consistent with the previously observed X-ray flux variability on a scale of months. Photon count rates are presented for each of five energy bands and count rate and photon spectra for the June through July 1978 observations are derived. A comparison of the data obtained with that at lower X-ray energies and higher gamma-ray energies indicates that there is an overall spectral steepening from low to high energies and a possible break near 20 keV, which may be due to the gamma rays originating from a different region than that of the X rays.
    Keywords: ASTROPHYSICS
    Type: Nature; 278; Mar. 15
    Format: text
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  • 12
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    A feature in the X-ray spectrum of Cygnus X-1 - A possible positron annihilation line (1983)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The paper presents a 10 keV to 1 MeV X-ray spectrum of Cyg X-1 in its low state, accumulated over 3 months in 1977 and 1978. The spectrum is smooth up to 300 keV. The excess at higher energy may be interpreted as a broad 511 keV emission line from the annihilation of positrons. The width and centroid of the line indicate that the temperature of the line-emitting region is 20-200 keV. The feature could also be caused by Comptonized emission from a 165 keV region.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 265
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  • 13
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    X-ray and gamma-ray upper limits for pulsed emission from radio pulsars (1982)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Results are given for an HEAO 1 search for pulsed emissions from 11 radio pulsars, in the 15 keV-11 MeV energy range. The upper limits of the Vela pulsar are found to fall below the low-energy extrapolation of the more than 50 MeV pulsed spectrum observed by the COS B satellite, and while consistent with predictions of a polar cap acceleration model, seem barely consistent with a single power-law interpolation between optical intensity and the 50 MeV intensity. High energy X-ray upper limits for seven of the ten other pulsars, which were chosen on the basis of proximity to earth, high rotational energy loss rates and short periods, are found to be only a few percent of their rotational energy losses, assuming a moment of inertia, an emission solid angle, and a pulse duty cycle, that are all similar to the high energy X-ray duty cycle of the Crab pulsar. These upper limits are below the corresponding fraction for the Crab pulsar in the cases of the Vela pulsar, PSR 1929+10 and PSR 1642-03.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 260
    Format: text
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  • 14
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    HEAO observations of X-ray bursts from MXB1730-335 (1978)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: The March 18, 1978 burst activity of the rapid burster MXB 1730-335 was studied by examining 58 minutes of quick-look data for the A2 and A4 experiments on HEAO 1. Very large, moderately sized, and small bursts are characterized. Type II bursts were found to show a spectral softening during burst decay. The existence of flux was sought in the 85-160 keV energy range, and it was found that the large type II bursts contain less than 5% of their total X-ray energy in this range. The implications of the lack of a hard X-ray flux with respect to accretion instability models of X-ray bursts are considered.
    Keywords: ASTROPHYSICS
    Type: Nature; 276; Dec. 7
    Format: text
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  • 15
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    X-rays and Gamma-rays from active galaxies (1983)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: Photon-photon pair production in active galaxies is considered, and the concept of the annihilation efficiency, the efficiency of the conversion of continuum luminosity of greater than 511 keV into positron annihilation luminosity, is introduced. Equations that give the source's annihilation luminosity and 511-keV flux as a function of its size, continuum luminosity and distance are developed. These are applied to the available X-ray and gamma-ray data on active galaxies in order to make specific predictions. Efficiencies as high as over 6 percent and fluxes up to 0.0008 ph/sq cm s result. While the latter are below present limits, they are within the reach of advanced instruments now in development.
    Keywords: ASTROPHYSICS
    Type: Positron-electron pairs in astrophysics; Jan 06, 1983 - Jan 08, 1983; Greenbelt, MD
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  • 16
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    An observation of annihilation radiation from the Galactic center region (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Results are reported from observations of the 511 MeV annihilation gamma-ray line from the Galactic center, made on May 22, 1989 with a high-resolution gamma-ray spectrometer on board a balloon launched from Alice Springs (Australia). The observations were made at about 4 gm/sq cm atmospheric depth for 6 hrs in a series of target and background pointings lasting 20 min each. The results obtained from multiparameter Gaussian fits to the data were as follows: 511 keV flux = 0.00089 + or - 0.00027 ph/sq cm per sec-rad, line width of about 1.1 keV, and less than 3.2 keV FWHM at 95 percent confidence.
    Keywords: ASTROPHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 11; 8 19
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  • 17
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    An observation of the Galactic center region with the HEXAGONE high resolution gamma-ray spectrometer (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: The Galactic center region was observed for 6 hours on May 22, 1989 from a high altitude balloon with the HEXAGONE high resolution gamma-ray spectrometer. The instrument had a 285 sq/cm array of cooled germanium detectors with an energy resolution of 2.2 keV at 511 keV and an 18 deg FWHM field of view. The 511 keV gamma-rays from electron-positron annihilation and 1809 keV gamma-rays from the radioactive decay of Al-26 were observed to have fluxes of 8.9 x 10 exp -4 and 1.9 x 10 exp -4 ph/cm-s, respectively. Continuum emission was detected from 20 to 800 keV and preliminary results have been obtained for the spectrum. Below 120 keV this is well described by power law with a slope of -2.6. In the 120-250 keV band the spectrum contains a broad linelike feature. This is interpreted as the result of Compton backscattering of about 511 keV photons from a compact source of electron-positron annihilation radiation.
    Keywords: ASTROPHYSICS
    Type: International Symposium on Gamma-Ray Line Astrophysics; Dec 10, 1990 - Dec 13, 1990; Paris; France
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  • 18
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    BATSE spectroscopy detector calibration (1992)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: We describe the channel-to-energy calibration of the Spectroscopy Detectors of the Burst and Transient Source Experiment (BATSE) on the Compton Gamma Ray Observatory (GRO). These detectors consist of NaI(TI) crystals viewed by photomultiplier tubes whose output in turn is measured by a pulse height analyzer. The calibration of these detectors has been complicated by frequent gain changes and by nonlinearities specific to the BATSE detectors. Nonlinearities in the light output from the NaI crystal and in the pulse height analyzer are shifted relative to each other by changes in the gain of the photomultiplier tube. We present the analytical model which is the basis of our calibration methodology, and outline how the empirical coefficients in this approach were determined. We also describe the complications peculiar to the Spectroscopy Detectors, and how our understanding of the detectors' operation led us to a solution to these problems.
    Keywords: SPACECRAFT INSTRUMENTATION
    Type: Experimental Astronomy (ISSN 0922-6435); 2; 5; p. 307-330.
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  • 19
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    High energy X-ray observations of extragalactic objects (1979)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Preliminary results are reported for scanning observations of the active galaxy NGC 5128 (Cen A) and the Type 1 Seyfert galaxy NGC 4151 with the low-energy detectors of the HEAO-1 A-4 hard X-ray instrument. The X-ray spectra in the energy range from 15 to 100 keV are shown to be consistent with previous observations of these galaxies. It is noted that NGC 5128 rose in intensity from 1972 to 1975, that spectral softening occurred after early 1973, and that the source has since decreased in intensity while maintaining an E to the -1.7 photon power law. The results for NGC 4151 indicate variable absorption below 10 keV and a power-law slope of about E to the -1.4 in the range from 10 keV to 10 MeV.
    Keywords: ASTROPHYSICS
    Type: X-ray astronomy; May 29, 1978 - Jun 10, 1978; Innsbruck; Austria
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