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  • 1
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    Positions of galactic X-ray sources - l/II/ between 320 and 340 deg (1978)
    In:  Other Sources
    Details
    Publication Date: 2011-08-17
    Description: The precise (20-40 sec) positions of seven X-ray sources in the celestial region corresponding to the galactic longitude range from 320 to 340 deg are reported. The sources include a recurrent transient X-ray source (MX1608-52) and a source 2S1553-542 coincident with a gamma-ray source within the given errors of position. The positions reported reduce the previously reported areas of the error region for six of the sources by factors ranging from 10 to 100. The presented results add confidence to the proposed radio candidates for 4U1624-49 and 4U1642-45 considered by Sanduleak and Dolan (1974) and Seaquist (1977).
    Keywords: ASTRONOMY
    Type: Nature; 271; Jan. 19
    Format: text
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  • 2
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    Observation of X-ray eclipses from LMC X-4 (1978)
    In:  Other Sources
    Details
    Publication Date: 2011-08-17
    Description: Observations made with the Rotation Modulation Collimator system (RMC) have revealed that X-ray source X-4 in the Large Magellanic Cloud (LMC X-4) is most likely part of a binary system. An analysis of the star's coordinates is presented, with attention given to orbital period and flux intensity variations. Stellar mass and orbital inclination angle are estimated for both X-4 and its companion star.
    Keywords: ASTRONOMY
    Type: Nature; 271; Jan. 5
    Format: text
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  • 3
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    Deep X-ray survey of the Small Magellanic Cloud (1979)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: An extended survey of the Small Magellanic Cloud with the SAS 3 X-ray observatory detected SMC X-1 but no other source with a luminosity greater than 1.0 x 10 to the 37th ergs/sec. In particular, SMC X-2 and SMC X-3, observed one month earlier at luminosities of 7 x 10 to the 37th and 10 x 10 to the 37th ergs/sec, respectively, were not detected, which proves that they are both highly variable. The results indicate that the maximum luminosities of early-type X-ray stars in the SMC congregate near 10 to the 38th ergs/sec, which is about five times the maximum luminosity of similar sources in the Galaxy.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal; vol. 227
    Format: text
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  • 4
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    The X-ray, optical, and radio behavior of Scorpius X-1 - The 1972 coordinated observations (1975)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Keywords: ASTRONOMY
    Type: Astrophysical Journal; 197; Apr. 15
    Format: text
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  • 5
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    Simultaneous X-ray and optical observations of the 7.7 second X-ray pulsar 4U 1626-67 (1980)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: Simultaneous X-ray and optical observations of the 7.7-s X-ray pulsar 4U 1626-67, obtained during May 29-31, 1978, reveal the presence of (1) intense, correlated optical and X-ray flares and (2) 7.7-s optical pulsations which agree in phase with the 1-3 keV X-ray pulsations to within 0.5 s (two standard deviations) and which agree in period to within 0.001 s (one standard deviation). From these data it is concluded that a substantial fraction (a minimum of 8%) and possibly all of the optical emission is produced from within approximately 0.5 light sec or 1.5 x 10 to the 10th cm of the neutron star. Furthermore, the data rule out the possibility that this optical emission comes from the X-ray heated surface of a degenerate or nondegenerate dwarf companion. It most likely comes from an accretion disk.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal; vol. 235
    Format: text
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  • 6
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    On two new X-ray sources in the SMC and the high luminosities of the Magellanic X-ray sources (1978)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: The discovery of two new X-ray sources, SMC X-2 and SMC X-3, in the Small Magellanic Cloud is reported. They have hard spectra, and their luminosities in the energy range 2-11 keV are 1.0 and 0.7 by 10 to the 38th power erg/sq cm per sec, respectively. It is shown that the luminosity distribution of the known Magellanic X-ray sources, which are now nine in number, is shifted toward higher luminosities with respect to that of similar sources in the Galaxy, and that the cause of the shift is probably an underabundance of heavy elements in the material accreted by the X-ray sources.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal; vol. 221
    Format: text
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  • 7
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    Observations of variable X-ray sources in globular clusters (1975)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: The discovery is reported of a variable X-ray source at midgalactic latitude in the globular cluster NGC 1851, and observations are reported which confirm the existence of variable X-ray sources in NGC 7078 and NGC 6441. The new source, designated MX 0513-40, was found to vary in intensity by a factor of at least 5 over a sixteen-day period and to have a hard spectrum as compared to that of the Crab Nebula in the energy range from 1 to 10 keV. The source in NGC 7078 (3U 2131+11) was found to vary by more than a factor of 2 over a 500-day period. Strong evidence of variability is presented for the source in NGC 6441 (3U 1746-37). It is concluded that both MX 0513-40 and 3U 2131+11 are probably stellar objects and are no more than about 160 kpc distant.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal; 199; July 15
    Format: text
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  • 8
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    OSO-7 observations of high galactic latitude X-ray sources (1976)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: Six hundred days of observations by the X-ray detectors aboard OSO-7 have been analyzed. All-sky maps of X-ray intensity have been constructed from these data. A sample map is displayed. Seven sources with galactic latitude greater than 10 deg, discovered during the mapping process, are reported, and upper limits are set on other high-latitude sources. The OSO-7 results are compared with those of Uhuru, and an implication of this comparison, that many of the high-latitude sources may be variable, is discussed.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal; 206; May 15
    Format: text
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  • 9
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    OSO-7 observations of the X-ray nova 3U 1543-47 (1976)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: The intensity and spectrum of the transient X-ray source 3U 1543-47 were measured by X-ray detectors on the OSO-7 satellite on 13 occasions between November 1971 and December 1972. The results, together with observations of the same object by the Vela and Uhuru satellites, can be described in terms of four qualitatively distinct phases in the X-ray light curve: (1) outburst; (2) relatively steady intensity and spectrum; (3) rapid decrease in intensity and decrease in apparent temperature; and (4) irregular intensity fluctuations with complex spectra. The term 'X-ray nova' is proposed to characterize this and similar transient sources, and a new model for such X-ray novae is proposed.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal; 203; Jan. 1
    Format: text
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  • 10
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    Discovery of a 7.68 second X-ray periodicity in 3U 1626-67 (1977)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: SAS-3 observations of the X-ray source 3U 1626-67 have revealed the presence of a stable 7.68-sec pulse period. This source was selected for study because of its hard X-ray spectrum. The compilation of source spectra used in the selection process is also presented. Pulse arrival times are analyzed for effects of possible binary orbital motion. Upper limits to the projected orbital radius are obtained which tend to exclude orbital periods in the range from about 0.5 to 35 days. Binary systems with either a very long orbit (at least 175 days) or a very short orbit (no more than about 0.3 day) are most probable
    Keywords: ASTRONOMY
    Type: Astrophysical Journal; vol. 217
    Format: text
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