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  • Other Sources  (32)
  • NASA Technical Reports  (32)
  • ASTRONOMY  (32)
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  • Other Sources  (32)
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  • NASA Technical Reports  (32)
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  • 1
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    RX J0045.4+4154: A recurrent supersoft x-ray transient in M31 (1995)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: Using data extracted from the ROSAT archive we have discovered a recurrent supersoft X-ray transient RX J0045.4+4154 in M31. The first outburst began on 1992 February 2 and continued for at least 4 days, until the end of the observation sequence. A second outburst that lasted more than 6 days was seen to begin on 1993 January 7. The X-ray spectrum on both occasions yields a characteristic blackbody temperature of approximately 90 eV. For a range of plausible continuum models, the hydrogen column density is (0.8-1.5) x 10(exp 21)/sq cm and is consistent with the source being located in M31. This implies an unabsorbed 0.1-2.0 keV peak luminosity of approximately 10(exp 38) ergs/sec. This is the first recurrent X-ray transient to be found in M31 and is particularly notable because it is much softer than the bright X-ray transients seen in our Galaxy. The spectrum is characteristic of the supersoft class of X-ray sources, which are thought to be accreting white dwarfs that have a hydrogen-burning surface layer. A fit to a white dwarf model atmosphere gives a temperature of 10(exp 6)K, the hottest found so far. This high temperature is consistent with a white dwarf mass of 1.3-1.4 solar mass, approaching the Chandrasekhar limit, and burning close to the nuclear stability limit.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 445; 2; p. L25-L28
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  • 2
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    Results from ASCA (1995)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: The X-ray observatory Advanced Satellite for Cosmology and Astrophysics (ASCA) (Astro-D) was launched in Feb 1993 and is now providing excellent spectro-imaging observations of objects from virtually every astronomical class. This paper reviews the scientific capabilities of ASCA using some of the first results from X-ray binaries, cataclysmic variables, and stars.
    Keywords: ASTRONOMY
    Type: Advances in Space Research (ISSN 0273-1177); 16; 3; p. 29-39
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  • 3
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    A ROSAT observation of delta Orionis A (1993)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: Delta Orionis A was observed with ROSAT in February 1991 at ten different phases of the 5.7 day binary orbit. The soft X-ray emission shows little dependence on binary phase favoring models for the production of the soft X-rays in the outer parts of the stellar wind. The energy spectrum obtained with the Position Sensitive Proportional Counter (PSPC) shows two thermal components with temperatures of 0.1 and 0.2 keV. The temperature and absorption of the hotter component is consistent with the Einstein solid state spectrometers (SSS) spectrum obtained in 1979. The two temperatures suggest either two emission regions with different temperatures, or one emission region with a temperature distribution where the hotter parts are closer to the OB stars than the cooler parts as indicated by the higher absorption of the hotter spectral component. This would be in contrast to stellar wind shock models which predict shock temperatures increasing with distance to the star.
    Keywords: ASTRONOMY
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 280; 2; p. 519-522
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  • 4
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    Resolving the Cygnus X-3 iron K line (1994)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: An Advanced Satellite for Cosmology and Astrophysics (ASCA) observation of Cygnus X-3 on 1993 June 11, in its X-ray high intensity state, has for the first time resolved the broad iron K line emission into three components: a He-like line at 6.67 +/- 0.01 keV, a H-like line at 6.96 +/- 0.02 keV, and a neutral line at 6.37 +/- 0.03 keV. The line intensities of the 6.67 keV and 6.96 keV lines are modulated with the 4.8 hr orbital period and are maximum when the continuum intensity is minimum. There is a sharp minimum of the line intensity on the rising phase of the continuum intensity. An iron absorption edge is observed at 7.19 +/- 0.02 keV. The optical depth of the absorption edge varies from 0.3 to 0.5 and is in anti-phase with the overall X-ray continuum modulation. The observed complexity of the iron K line region is greater than that had been assumed in previous spectral modeling based on observations with lower resolution detectors.
    Keywords: ASTRONOMY
    Type: PASJ: Publications of the Astronomical Society of Japan (ISSN 0004-6264); 46; 3; p. L105-L108
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  • 5
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    Copernicus observations of a number of galactic X-ray sources (1976)
    In:  CASI
    Details
    Publication Date: 2006-04-18
    Description: The Copernicus satellite was launched on 21 August 1972. The main experiment on board is the University of Princeton UV telescope. In addition a cosmic X-ray package of somewhat modest aperture was provided by the Mullard Space Science Laboratory (MSSL) of University College London. Following a brief description of the instrument, a list of galactic sources observed during the year is presented. Although the X-ray detection aperture is small, the ability to point the satellite for long periods of time with high accuracy makes Copernicus an ideal vehicle for the study of variable sources.
    Keywords: ASTRONOMY
    Type: NASA. Goddard Space Flight Center X-ray Binaries; p 1-25
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  • 6
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    The discovery and properties of the ultra-soft X-ray transient EXO 1846-031 (1993)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: We report the discovery of a previously uncataloged ultra-soft X-ray transient EXO 1846-031 which was in outburst during 1985 April to September. The X-ray spectrum consists of an ultra-soft component and a high-energy power-law tail that extends to at least 25 keV. The ultra-soft component may be modeled by either a cutoff power-law or a multicolor blackbody disk model. The latter model allows the evolution in spectrum and intensity observed during the outburst to be accounted for by the change in a single parameter - the temperature at the innermost disk radius. We demonstrate that at least one other accretion disk model is able to account for these changes by the variation of a single parameter. During one of the three EXOSAT observations, EXO 1846-031 exhibited significant intensity variability which probably originates from the power-law component. We derive a position for this unidentified source and present the results of a search for the optical counterpart.
    Keywords: ASTRONOMY
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 279; 1; p. 179-187
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  • 7
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    Accretion disk corona line emission from X0614+091 (1994)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: The low-mass X-ray binary X0614+091 was observed on 3 days in 1979 with the Einstein Observatory solid state spectrometer and the monitor proportional counter. During the observation with the highest measured flux, corresponding to an X-ray luminosity of 8 x 10(exp 36) erg/s (in the 0.5-20 keV band for an assumed distance of 5 kpc), significant low-energy emission was detected, centered at 0.77 keV, possibly due to line emission for O VII-O VIII and Fe XVII-Fe XIX. The other observations, which were at fluxes lower by a factor of 2, are consistent with the presence of the emission feature. The equivalent width of the feature, 37 +/- 6 eV, is of the same order as equivalent widths previously reported for more luminous low-mass X-ray binaries using grating spectrometer data. The soft X-ray lines could be emitted by gas expected to arise in an accretion disk corona excited by the central source. But to explain the observed feature, most of the corona needs to contribute, or other sources of emission are required.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 422; 2; p. 791-798
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  • 8
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    The identification of H2311 + 77 with HD220140, a probable RS CVn star (1985)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: H2311 + 77, one of the bright soft X-ray sources in the sky originally detected with HEAO 1, has been identified in an Exosat imaging observation with a 7.7-mag late-type star, HD220140. The X-ray luminosity and the optical characteristics of this star indicate that it is probably an RS CVn binary system.
    Keywords: ASTRONOMY
    Type: Royal Astronomical Society, Monthly Notices (ISSN 0035-8711); 215; 11P-13P
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  • 9
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    Two-component X-ray emission from RS Canum Venaticorum binaries (1981)
    In:  Other Sources
    Details
    Publication Date: 2011-08-18
    Description: A summary is presented of results from the Solid State Spectrometer on the Einstein Observatory for seven RS CVn binaries. The spectra of all require two emission components, evidenced by line emission characteristics of plasma at 4-million to 8-million K and bremsstrahlung characteristic of 20-million to 100-million K. The data are interpreted in terms of magnetic coronal loops similar to those seen on the sun, although with different characteristic parameters. The emission regions could be defined by separate magnetic structures. For pressures less than 10 dynes/sq cm the low temperature plasma would be confined within the stellar radii, while the high temperature plasma would, for the synchronous, close binaries, fill the binary orbits. However, for loop pressures exceeding 100 dynes sq cm, the high temperature components would also be confined to within the stellar radii, in loops covering only small fractions of the stellar surfaces. While the radio properties and the occurrence of X-ray flares suggest the larger emission regions, the observations of time variations leave the ambiguity unresolved.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal; vol. 246
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  • 10
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    The observed properties of X-ray pulsars (1982)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: A unified description of the properties of the 14 X-ray pulsars is summarized. Properties of X-ray pulsars and obvious correlations with luminosity are outlined.
    Keywords: ASTRONOMY
    Type: Max-Planck Inst. Phys. and Astrophys. Accreting Neutron Stars; p 29-40
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