Engineering topics

Boynton, P. E.

Publications and source records attributed to Boynton, P. E..

13 records

NASA NTRS1993

Discovery of orbital decay in SMC X-1

Three observations of the binary X-ray pulsar SMC X-1 with the Ginga satellite, conducted on 3 days in 1987 May, 8.4 days in 1988 August-September, and 4 days in 1989 July-August, are reported. Based on the three observation epochs, the rate of change in the orbital period is estimated at (-3.36 +/- 0.02) x 10 exp -6/yr. An interpretation of the orbital decay is made in the context of tidal evolution with allowance for the effect of the increasing moment of inertia of the companion star due to its nuclear evolution. While the orbital decay is thought to be driven by tidal interactions, it is suggested that the asynchronism between the orbit and the rotation of the companion star is most likely maintained by the evolutionary expansion of the companion star (Sk 160) rather than via the Darwin instability.

Levine, A.↗

NASA NTRS1993

Discovery of Orbital Decay in SMC X-1

We report on the results of three observations of the binary X-ray pulsar SMC X-1 with the Ginga satellite. Timing analyses of the 0.71 s X-ray pulsations yield Doppler delay curves which, in turn, enable the most accurate determination of the SMC X-1 orbital parameters available to date. Epochs of phase zero for the 3.9 day orbit were determined for 1987 May, 1988 August, and 1989 August with accuracies of 13, 0.6, and 3 s, respectively. These epochs are combined with two previous determinations of the orbital epoch to yield the rate of change in the orbital period dot-P(orb)/P(orb) = ( 3.36 +/- 0.02) x 10(exp -6) yr(exp -1). An interpretation of the orbital decay is made in the context of tidal evolution, with consideration of the influence of the increasing moment of inertia of the companion star due to its nuclear evolution. We find that, while the orbital decay is probably driven by tidal interactions, the asynchronism between the orbit and the rotation of the companion star is most likely maintained by the evolutionary expansion of the companion star (Sk 160) rather than via the Darwin instability. In this case Sk 160 is likely to be in the hydrogen shell burning phase of its evolution. Finally, a discussion is presented of the relation among the time scales for stellar evolution (less than 10(exp 7) yr), orbital decay (3 x 10(exp 5) yr), and neutron-star spin-up in the SMC X-1 system (2000 yr). In particular, we present the result of a self-consistent calculation for the histories of the spin of the neutron star and the mass transfer in this system. A plausible case can be made for the spin-up time scale being directly related to the lifetime of the luminous X-ray phase which will end in a common-envelope phase within a time of less than approx. 10(exp 4) yr.

Levine, A.↗

NASA NTRS1989

Correlation between X-ray flux and rotational acceleration in Vela X-1

The results of a search for correlations between X-ray flux and angular acceleration for the accreting binary pulsar Vela X-1 are presented. Results are based on data obtained with the Hakucho satellite during the interval 1982 to 1984. In undertaking this correlation analysis, it was necessary to modify the usual statistical method to deal with conditions imposed by generally unavoidable satellite observing constraints, most notably a mismatch in sampling between the two variables. The results are suggestive of a correlation between flux and the absolute value of the angular acceleration, at a significance level of 96 percent. The implications of the methods and results for future observations and analysis are discussed.

Deeter, J. E.↗

NASA NTRS1989

Vela X-1 pulse timing. II - Variations in pulse frequency

The pulsed X-ray emission of Vela X-1 during May 1978 and December-January 1978-1979 is investigated analytically on the basis of published satellite observations. The data are compiled in tables and graphs and discussed in detail, with reference to data for the entire 1975-1982 period. Variations in pulse frequency are identified on time scales from 2 to 2600 days; the lower nine octaves are characterized as white noise (or random walk in pulse frequency), while the longer-period variations are attributed to changes in neutron-star rotation rates.

Deeter, J. E.↗

NASA NTRS1987

Pulse-timing study of Vela X-1 based on Hakucho and Tenma data - 1980-1984

The extensive observations of Vela X-1 acquired from 1980 to 1984 with the Hakucho and Tenma satellites, using a pulse-filtering technique that provides a significant improvement in pulse-timing precision, are reexamined. The details of the preparation of this data base, including the determination of updated orbital parameters based on these and previously published observations covering a 10-yr interval, are reported. Preparatory to estimation of angular-acceleration flux-correlation pairs, substantially improved estimates of the power density of fluctuations in the derivative of the pulse frequency on analysis periods between 0.5 and 80 days are presented. These results support the phenomenological hypothesis that unresolved fluctuations in the angular acceleration of the neutron star, describable as random noise, are responsible for the entire history of the observed variation in pulse frequency of Vela X-1 on all time scales longer than a few days.

Deeter, J. E.↗

NASA NTRS1987

Apsidal advance in Vela X-1

An upper bound on the rate of apsidal advance in Vela X-1 is determined, taking into account the effect of the red noise in pulse frequency reported by Boynton et al. (1986). A new, more precise mean orbit is computed which provides substantially smaller upper bounds on both the rate of apsidal advance and the rate of change of the orbital period than previous solutions. A new, hybrid method for measuring the rate of apsidal advance is described that uses eclipse observations as well as pulse timing. The new method is potentially as useful as the direct measurement from pulse-timing alone for systems that allow more precise determinations of eclipse ingress and egress than does Vela X-1.

Deeter, J. E.↗

NASA NTRS1986

Vela X-1 pulse timing. I - Determination of the neutron star orbit

Analysis and interpretation of observations of the pulsed X-ray emission from Vela X-1 are presented. The interrelated tasks of determining the neutron-star orbit and calculating pulse emission times in the rest frame of the source are considered, with the underlying motivation to utilize this time series for analysis of fluctuations in the pulse emission frequency, which are interpreted as noise in the neutron-star rotation rate. However, the redness and strength of this noise in Vela X-1 pose a nontrivial complication, because the parameters of the neutron-star orbit are estimated by pulse timing and hence are themselves affected by fluctuations in the pulse emission frequency. A second challenge is presented by substantial fluctuations in the Vela X-1 pulse shape that, if ignored, would significantly reduce both the precision of the orbital solution and the ability to study fluctuations in the rotation rate. The report emphasizes the analysis techniques that have been developed to obtain the most precise orbital solution possible in the face of these difficulties. These techniques are general and may be applied to other pulsars that exhibit substantial fluctuations in pulse shape and frequency, such as Her X-1 and Cen X-3.

Boynton, P. E.↗

NASA NTRS1984

New evidence on the nature of the neutron star and accretion flow in Vela X-1 from pulse timing observations

It is believed that variations in the intrinsic pulse frequencies of neutron star X-ray sources reflect changes in the rotation rate of the stellar crust produced by torque originating outside and inside the star. The external torque depends on the flow pattern of the accreting plasma, while the internal torque depends on the state of the interior and its coupling to the crust. Information about the accretion flow and the star itself can, therefore, be obtained on the basis of a study of intrinsic frequency variations. The present investigation is concerned with the results of a detailed study of the 283 s pulsing X-ray star Vela X-1 using pulse timing techniques. It is found that the frequency variations in this source are consistent with the occurrence of a succession of temporally unresolved events which can be characterized mathematically as second-order red noise in the pulse phase.

Boynton, P. E.↗

NASA NTRS1982

Einstein Observatory pulse-phase spectroscopy of Hercules X-1

Spectra of the Her X-1 pulsations from 0.15 to 4.5 keV have been obtained with the Objective-Grating and Solid State Spectrometers on the HEAO 2 Einstein Observatory. The spectra show no distinct atomic emission or absorption features, except for broad emission near 1 keV possibly due to unresolved Fe L shell emission lines. Spectrally resolved pulse waveforms show a dramatic 240 deg phase shift for E less than 0.85 keV. The soft X-rays are interpreted as the result of the reprocessing of the hard X-ray beam by the inner disk at the magnetospheric boundary of the neutron star, and several spectroscopic and phase observations are suggested which could provide further knowledge of these structures.

Mccray, R. A.↗

NASA NTRS1982

X-ray observations of Abell 2218 and implications for the Sunyaev-Zel'dovich effect

The Einstein Observatory was used to obtain a high-resolution X-ray image and an X-ray flux measurement of the galaxy cluster Abell 2218. The combined system of intracluster medium and galaxies is modeled as a gas in hydrostatic equilibrium in a common gravitational potential with an isothermal galaxy component. This model is then fitted in the least-squares sense to the X-ray surface brightness distribution and to the optically determined galaxy surface density profile to determine model parameters. The gas is found to be nominally isothermal, moderately dense, and very hot (10-30 keV); these conditions are consistent with the Sunyaev-Zel'dovich effect, i.e., the diminution in the cosmic microwave background radiation intensity in the direction of this cluster. It is noted that the considerable imprecision inherent in the method of distance measurement based on the combination of microwave measurements with X-ray and optical data makes it impossible to make a definitive statement about the distance to Abell 2218.

Boynton, P. E.↗

NASA NTRS1981

Pulse-timing observations of Hercules X-1

Results are presented from pulse-timing analysis of Hercules X-1, based on satellite observations spanning 7 years. The binary orbital elements are redetermined and the near circularity of the orbit is confirmed with a new 2 sigma upper limit of 0.0003 on the eccentricity. We also report a much improved value of 1.70016779d + or - 0.00000001d for the orbital period, with a 2 sigma upper limit on its rate of change. Observations of transitions into and out of eclipse are used to determine an eclipse half-angle of 24.56 deg + or - 0.03 deg, somewhat smaller than previously reported values. The secular trend toward shorter pulse periods is found to be continuing.

Deeter, J. E.↗

NASA NTRS1981

X-ray observations and the cosmic distance scale

The physics of hot gas in the cores of distant clusters of galaxies can be studied in considerable detail through a specific combination of X-ray, microwave and optical observations. In principle, the X-ray luminosity of the gas can be calculated from these data, providing a measure of the cluster distance. These ideas and their application to Abell 2218, the only cluster for which even marginally suitable data yet exist are examined.

Boynton, P. E.↗

NASA NTRS1976

Orbital precession in Hercules X-1

It is noted that the 35-day X-ray high-low cycle of Her X-1 could be explained in terms of periodic obscuration of the source by a tilted and precessing 'slaved' accretion disk, which would require precession of the mass-shedding star and, consequently, a precessing binary orbit. Four months of Uhuru data obtained in 1972 are analyzed to determine whether the orbital precession can be detected as a Doppler modulation in the arrival times of the 1.24-sec X-ray pulsations. The precession geometry is examined, the test for precession is outlined, and a marginally significant indication of orbital precession in the Hz Her/Her X-1 system is obtained. Possible biases in the analysis are evaluated, and the spin-axis misalignment of HZ Her is estimated from the measured tilt of the orbit.

Deeter, J. E.↗