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  • 1
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    The linear X-ray polarization of Scorpius X-1 (1979)
    In:  Other Sources
    Details
    Publication Date: 2011-08-17
    Description: Scorpius X-1 was observed with the Bragg crystal polarimeters aboard OSO 8 in August 1977 and again in August 1978. An analysis of these observations reveals a time-averaged polarization of 0.39% plus or minus 0.20% at 2.6 keV and 1.31% plus or minus 0.40% at 5.2 keV. The corresponding position angles are 29 deg plus or minus 10 deg and 57 deg plus or minus 6 deg, respectively. Binary phase-dependent polarization was searched for but not observed.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 232
    Format: text
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  • 2
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    X-ray images of W28 and 3C400.2 - Two radio-shell supernova remnants with centrally-peaked X-ray emission (1985)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: X-ray images of the supernova remnants (SNRs) W28 and 3C400.2 were obtained using the Imaging Proportional Counter (IPC) on the Einstein Observatory. Despite the shell-like radio morphology of these remnants, their X-ray emission is centrally peaked. Two possible X-ray emission mechanisms are explored: synchrotron emission due to an active central pulsar, and thermal emission from a thin hot plasma filling the interior of the remnant. Comparisons of X-ray and radio properties of W28 and 3C400.2 with known Crab-like remnants suggest that synchrotron emission is not a very plausible X-ray emission mechanism. Optical and radio observations suggest that both SNRs exploded in a dense cloud and have evolved rapidly to the radiative stage. The X-ray morphology observed is similar to that predicted for SNRs in such an environment.
    Keywords: ASTROPHYSICS
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  • 3
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    The X-ray properties of normal galaxies (1982)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The results of an Einstein Observatory study of 51 nearby normal galaxies, including the Large and Small Magellanic Clouds and M31, are reported. The X-ray luminosity of normal galaxies is about 0.0002 of the optical luminosity and shows no strong correlation with morphological type. Approximately 30 new supernova remnants were recognized in the Magellanic Clouds. Over 90 sources were detected in M31, of which at least 20 are identified with globular clusters. The number of luminous sources detected in the nearest galaxies per unit mass are similar to the number found in the Galaxy. Individual X-ray sources in the arms of nearby spirals can be very luminous; seven with luminosities in excess of 10 to the 39th ergs/s have been found. The nuclei of some, but not all, normal galaxies are luminous X-ray sources. Possible reasons for this emission are considered.
    Keywords: ASTROPHYSICS
    Type: (ISSN 0273-1177)
    Format: text
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  • 4
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    The X-ray surface brightness of Kepler's supernova remnant (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The first X-ray images of Kepler's supernova remnant (SN Ophiuchi 1604) are presented, and consequences for SNR models are discussed. Observations made with the Einstein Observatory Imaging Proportional Counter and High Resolution Imager show the remnant to be circular, with a strong shell brighter in the north than in the south. A flux of 1.2 x 10 to the -10th ergs/sq cm per sec was measured in the 0.15-4.5 keV region, which corresponds to an X-ray luminosity of 1.0 x 10 to the 36th ergs/sec at a distance of 5 kpc and an interstellar medium density of 2.8 x 10 to the 21st/sq cm. The X-ray observations do not allow the determination of whether the SNR is in the adiabatic or free expansion phase, but in either case it is shown that the mean ISM density must be greater than about 0.1/cu cm. In addition, the density of the X-ray emitting gas must be high, and its electron temperature must be fairly low. The high ISM densities derived for Kepler's SNR and other SNRs thus suggest an atypical ISM, possibly influenced by mass lost from the pre-supernova star.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 264
    Format: text
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  • 5
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    X-ray observations of the 5 March 1979 gamma-burst field (1979)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: An extremely intense burst of hard X-rays and gamma-rays that was recorded by the nine interplanetary spacecraft of the burst sensor network and localized by time-of-flight determinations to a position coincident with the supernova remnant N49 in the Large Magellanic Cloud is analyzed. The region of the sky was observed both before and after the gamma-ray event with the soft X-ray imaging instruments aboard the Einstein Observatory. Coupled with the optical plate material, the soft X-ray data is used to place severe constraints on models for the origin of the transient phenomena.
    Keywords: ASTROPHYSICS
    Type: Nature; 282; Dec. 6
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  • 6
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    A survey of soft X-ray emission from hot stars (1980)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: Sixteen O and B stars were observed with the Einstein X-ray observatory; X-ray emission from all seven O stars and four of the B stars was discovered. The 0.15-4.5 keV luminosities range from approximately 10 to the 28th to 2 x 10 to the 32nd ergs/s and constitute 10 to the -6th to 10 to the -8th of the total luminosities of the stars detected. Most of the photons emerge at energies less than 1 keV, in contradiction to the prediction made by Cassinelli and Olson (1979) based on a hot corona-cool wind model.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 239
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  • 7
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    The X-ray polarization of the Cygnus sources (1980)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: Multiple observations of Cygnus X-1, Cygnus X-2, and Cygnus X-3 were carried out with the Bragg crystal polarimeters aboard OSO 8. Of these sources, an unambiguous detection of the time-averaged polarization was obtained only for Cygnus X-1, which has a polarization of 2.4% plus or minus 1.1% at 2.6 keV and 5.3% plus or minus 2.5% at 5.2 keV. While statistically significant evidence for polarization of Cygnus X-2 of 4.9% at 2.6 keV was obtained in a 1975 observation, this result was not confirmed in later observations. For Cygnus X-3, modulation of the observed flux at twice the rotation frequency of the satellite, the signature of polarization, was also detected, but spurious modulation due to the presence of additional sources in the field of view cannot be ruled out.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 238
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  • 8
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    Supernova remnants in the Large Magellanic Cloud (1979)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: X-ray emission from 10 previously identified supernova remnants (SNR) in the Large Magellanic Cloud has been discovered in a partially completed survey of this nearby galaxy with the imaging proportional counter on the Einstein Observatory. The X-ray luminosities (0.5-3.0 keV) of these remnants range from 3 x 10 to the 35th to 4 x 10 to the 37th ergs/s. N157B and N158A, whose identifications as SNR were previously based solely on their radio spectra, have been detected as strong X-ray emitters. Two other objects from an optically selected list of candidate SNR were found to coincide with X-ray sources and therefore probably are SNR. The value of obtaining such a uniform sample of SNR at a known distance is illustrated by comparing the properties of the remnants and by fitting standard evolutionary models to the results.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 234
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  • 9
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    The effects of ejecta on the X-ray luminosities of supernova remnants (1982)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Because X-ray luminosities of most SNRs are dominated by emission from heavy elements, estimates of the X-ray emitting mass based on cosmic abundances may be incorrect. Here we investigate the apparent density evolution of a SNR when substantial amounts of processed material are ejected by the supernova. If this material is shock heated, it will dominate X-ray emission from the remnant long after the SNR has swept up the equivalent amount of interstellar matter (ISM). Emission from metal-rich ejecta may explain why ISM densities of young remnants far from the galactic plane, deduced from standard analysis, are higher than expected, as well as why larger SNRs appear to be lying in regions of lower ISM density. It should be included in detailed calculations of SNR surface brightness distributions, along with effects due to departures from ionization equilibrium and cloudlet evaporation in a multiphase ISM which may also contribute to the apparent evolution of density with radius.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 260
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  • 10
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    X-ray spectral classification of supernova remnants in the Large Magellanic Cloud (1982)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The solid state spectrometer on the Einstein Observatory was used to measure the 0.6-4.5 keV X-ray spectra of six prominent supernova remnants in the Large Magellanic Cloud, namely, N132D, N63A, N49, 0525-66.0, N157B, and 0540-69.3. Thermal emission is detected from the first four remnants and is similar in nature to that observed from young galactic SNRs. In contrast, N157B and 0540-69.3 have featureless X-ray spectra which are well described by power-law models. The present data support a synchrotron origin for the X-rays from N157B and 0540-69.3, although an alternative emission mechanism is considered for the latter object.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 255
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