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  • 1
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    Does Supernova 1987A contain a rapidly vibrating neutron star? (1989)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: If the recently reported 0.5 ms-period pulsed optical signal from the direction of Supernova 1987A originated in a young neutron star, its interpretation as a rotational period has difficulties. The surface magnetic field would have to be much lower than expected, and the high rotation rate may rule out preferred nuclear equations of state. It is pointed out here that a remnant radial vibration of a neutron star, excited in the supernova event, may survive for several years with about the observed (gravitationally redshifted) period. Heavy ions at the low-density stellar surface, periodically shocked by the vibration, may efficiently produce narrow pulses of optical cyclotron radiation in a surface field of about a trillion gauss.
    Keywords: ASTROPHYSICS
    Type: Nature (ISSN 0028-0836); 338; 319
    Format: text
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  • 2
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    Optical counterparts of the Large Magellanic Cloud X-ray point sources (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The results of a program of optical identification of the X-ray point sources in the direction of the Large Magellanic Cloud (LMC) are presented. Observational results are combined with accurate positions of about 3-arcsec obtained with the Einstein Observatory Imaging Proportional Counter (IPC). The sources include 13 foreground stars, three background active galaxies, and six LMC members which are known or suspected to be binaries. The 24 other sources in the Einstein LMC survey have only 30-arcsec positions and on average are less luminous and in more crowded regions of the LMC. On the basis of the new identifications, comparisons are made between the overall stellar X-ray population in the LMC and in the Galaxy. Although the mean X-ray luminosity of the LMC sources is significantly higher than that of the Galaxy, the total number of stellar X-ray systems per unit mass is similar in the LMC and the Galaxy.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 286; 196-208
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  • 3
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    The detection of pulsed X-ray emission from a nearby radio pulsar (1994)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: As part of a search for thermal surface radiation from nearby neutron stars, we have carried out a 45,000 s observation of the nearby radio pulsar PSR 1929+10 with the ROSAT PSPC. After background subtraction, a net of 420 +/- 25 photons in the 0.1 to 2.0 keV band were detected at the position of the pulsar, corresponding to a luminosity of 1.2 x 10(exp 30) ergs/sec for a source distance of 250 pc, or approximately 3 x 10(exp -4) of the pulsar's spin-down luminosity. We find coherent pulsations from PSR 1929+10 at the radio period of 0.2265 s. The folded light curve is well fitted by a sinusoidal oscillation with a pulsed fraction of about 30%. The total spectrum is fitted by a blackbody with a temperature T(sub infinity) approximately equals 3.2 x 10(exp 6) K; the implied emitting area has a radius of less than 50 m. The maximum of the X-ray light curve coincides with the radio pulse, suggesting that we are detecting the hot magnetic polar cap of the star. The temperature limit for the remainder of the stellar surface is T(sub infinity) less than 3 x 10(exp 5) K. The spatial distribution of the photons is consistent with the instrument point-spread function. We discuss the implications of these results for the temperature distribution over the surface of the star and use this detection to constrain various heating mechanisms for rotation-powered neutron stars. We also use a simple model of general relativistic light bending near the stellar surface in conjunction with the radio emission geometry and the X-ray pulsed fraction to derive a radius for the neutron star of R = 9 +/- 3 km.
    Keywords: ASTROPHYSICS
    Type: The Astrophysical Journal (ISSN 0004-637X); 429; 2 pt; p. 832-843
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  • 4
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    The intensity and spectrum of the diffuse X-ray background (1991)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: The paper reports the first measurement of the intensity and spectrum of the diffuse X-ray background in the 0.16-3.5 keV band which is free from contamination by sources with fluxes greater than 4 x 10 to the -14th ergs/sq cm s. These results have been made possible by a number of techniques for reducing cosmic-ray contamination and instrumental artifacts in the data collected by the Einstein Observatory imaging proportional counter.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 379; 564-575
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  • 5
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    Faint X-ray source counts and the origin of the X-ray background (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: A thorough reanalysis of the Einstein Observatory Deep Survey data is presented in order to determine the contribution of detected, discrete sources of X-ray emission to the cosmic X-ray background. Substantial discrepancies with previously published work on this problem are found. A detailed discussion of data editing and source algorithms buttresses a claim of having constructed a complete, flux-limited sample of the faintest sources detectable with the Einstein imaging proportional counter, the most sensitive X-ray instrument yet flown. A total of 33 sources is found in a survey region of about 3.3 sq deg down to a minimum flux threshold of 4 x 10 to the 14th ergs/sq cm/s in the 0.3-3.5 keV band. Roughly 30 percent of the objects are foreground stars, leading to an extragalactic source surface density of 70,000/sr at this threshold. The integrated contribution from discrete sources to the number of cosmic X-ray background photons measured in this same band with the same instrument is 12 percent + or - 3 percent, substantially below previous estimates. Implications of these results for the origin of the background are discussed.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 379; 576-585
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  • 6
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    The origin of the diffuse X-ray background (1987)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: The Einstein Deep Survey fields are used to reexamine the problem of the origin of the extragalactic diffuse X-ray background. An approach based on fluctuation analysis is adopted, and a sophisticated Monte Carlo scheme is used to compare the X-ray images with a variety of models representing point and diffuse source contributions. Results are presented for two classes of models: those which determine the flux cutoff beyond which pointlike sources fail to contribute significantly if the log N-log S slope is fixed at the measured value of -1.5, and those which set limits on the slope of the log N-log S relation below its last measured point at the Deep Survey threshold. In both cases, it is found that the known population of X-ray-emitting quasars and any reasonable extrapolations therefrom do not comprise the entire X-ray background.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 318; 93-102
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