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  • 1
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    Correlations between x-ray outbursts and relativistic ejections in the x-ray transient GRO J1655-40 (1995)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The detection of x-ray and radio emission from the recently discovered transient source X-ray Nova Scorpii 1994 (GRO J1655 - 40), is reported.
    Keywords: Astronomy
    Type: NASA-TM-111279 , NAS 1.15:111279
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  • 2
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    Observations of 4U 1700-37 with BATSE (1996)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The eclipsing binary X-ray source 4U 1700-37 has been continually monitored by the BATSE experiment on the Compton Gamma Ray Observatory since the spring of 1991. Using source measurements at times of Earth occultation, we observe an average (uneclipsed) flux of 0.23 crab in the 20-120 keV band. The flux is highly variable, with occasional flaring behavior on timescales from hundreds of seconds to several hours and intensities as bright as 1 crab. The uneclipsed spectrum is well represented by an optically thin thermal bremsstrahlung model with a temperature of 25 keV independent of source intensity or orbital phase. An upper limit of 4% on the pulse fraction has been obtained for pulse periods between 2 and 700 s. Average orbital light curves from almost 1000 days of occultation measurements have been constructed. These profiles are used to measure: (1) the eclipse semiangle, Theta(sub E) = 28.6 deg +/- 2.1 deg in the 20-120 keV band, and (2) the decrease in orbital period, P(dot)/P = -(3.3 +/- 0.6) x 10(exp -7) 1/ yr. Estimates of system physical parameters are obtained using Monte Carlo simulations to propagate errors in measured and assumed parameters. For the X-ray source mass we find M(sub x) = 2.6(sub -1.4)(sup +2.3) solar mass, and for the mass and radius of the optical companion, M(sub 0) = 30(sub -7)(sup +11) solar mass and R(sub 0) = 18(sub -2)(sup +2) solar radius.
    Keywords: Astronomy
    Type: NASA-TM-112507 , NAS 1.15:112507 , The Astrophysical Journal; 459; 259-270
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  • 3
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    A Maskless Gamma-Ray All-Sky Imager: BATSE/CGRO (1994)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The non-collimated detectors of BATSE (Burst And Transient Source Experiment) on the Compton Gamma Ray Observatory (CGRO) can be used as a high sensitivity hard X-ray and low energy gamma-ray all-sky imager in the energy range between 20 keV and 2 MeV. The fluxes from sources in the sky are modulated as the spacecraft orbits the Earth. The CGRO orbital precession further allows sampling of sky in strips corresponding to the limb of the earth at any given time. The modulation data are transformed into images by various reconstruction methods. High sensitivity images of location accuracy of about 0.1 deg and source seperation of about 1 deg are obtained.
    Keywords: Astronomy
    Type: NASA-CR-204027 , NAS 1.26:204027 , IEEE Transactions on Nuclear Science (ISSN 0018-9499); 41; 4; 1313-1320
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  • 4
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    Observation of a Long-Term Spin-up Trend in 4U 1538-52 (1997)
    In:  Other Sources
    Details
    Publication Date: 2019-07-17
    Description: The high-mass X-ray pulsar 4U 153 8-52 has been continually monitored by the Burst and Transient Source Experiment (BATSE) on Compton Gamma-Ray Observatory. These observations permit the construction of long-term pulse frequency and intensity histories. The frequency history reveals that a reversal of the long-term trend in the accretion torque, from spinning down to spinning up, has occurred, probably in 1988. This is the first time a long-term change is known to have occurred for this source, The magnitude of the average absolute value of (dot-nu / nu) is approximately 10(exp -11)/s over an interval of approximately 5 year is similar during spin-down and spin-up. Shorter term pulse frequency variations of either sign are also observed. The power density spectrum of fluctuations in angular acceleration is consistent with white noise on timescales from 16 to 1600 days. It can be well fit with a power law with a power-law index of 0.10 plus or minus 0.21 and white noise strength of (7.6 +/- 1.6) x 10(exp -21) (Hz/s(exp 2)/Hz). These observations are also used to set 95% confidence level lower and upper limits on the rate of orbital period change, -3.9〈 dot-P orb /P orb 〈2. 1, in units of 10(exp -6) yr(exp -1).
    Keywords: Astronomy
    Type: Astrophysical Journal; 488; 413-418
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