High-Energy Astrophysics American and Soviet Perspectives/Proceedings from the U.S.-U.S.S.R. Workshop on High-Energy Astrophysics (1991) / Chapter Skim
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ON THE OBSERVATIONAL APPEARANCES OF A FREELY PRECESSING NEUTRON STAR IN . . .
ON THE OBSERVATIONAL APPEARANCES OF A FREELY PRECESSING NEUTRON STAR IN . . .
Pages 307-315
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From page 307... ...
The precise formula for the period derivative due to free precession is obtained under the assumption that the precession period is much longer than that of the neutron star rotation. The optical light curves to be seen from the binary, with freely processing accreting neutron star are simulated numencally.
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From page 308... ...
We show that the pulsar period variations with the precession phase has a special shape by measuring which one could check up the model In the framework of this model we also simulate numerically optical light cubes to be observed from such a binary, taking into account the reflection effect on the secondary star and on the disk itself, and investigate the impact of the X-ray emission diagram on the light curves. PERIOD DERIVATIVE OF THE PULSAR DUE TO FREE PRECESSION Consider a freely processing biaxial solid body rotating around awns OF (see Figure 1)
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From page 309... ...
But this is not the case for a processing neutron star. Making use of familiar spherical trigonometric formulae one easily finds dA/dt sin X cos ,o-sin ~ cos X cos at (1)
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From page 310... ...
OPTICAL LIGHT CURVES HZ HER IN THE MODEL OF A FREELY PROCESSING NEUTRON STAR Synthesis of the light curies to be seen from binaries is a well-developed field of modern astrophysics (see e.g., Antothina and Cherepashchok 1987
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From page 311... ...
. Here we present some preliminary results showing synthetical optical light curves from Her X-1/HZ Her system In the framework of the processing neutron star model.
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DISCUSSION There are two general objections to the freely processing neutron star model First is that the difference of moments of inertia HI required to give rise to the precession frequency observed is LEVI ~ w/Q ~ 4~10-7 which cannot be sustained by stresses in the neutron star crust (G.S. BisnovatyiKogan)
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From page 313... ...
the free precession with the observed period in Her X-1 during the mass infall onto the star's surface throughout the magnetic poles (Novikov 1973~. This idea nicely fits with the observational absence of free precession in radiopulsars.
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From page 314... ...
0° 2 ~ i . O \ b - 60° _ b A 75° / / 0.25 0.5 0.75 / \ 0.25 0.5 0.75 In a stationary situation, the electrodynamical interaction of a rotating neutron star having a dipole magnetic field with a diamagnetic accretion disk, tends to make the dipole ens coplanar to the disk plane (Lipunov and Shakura 1980~.
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From page 315... ...
This expression can be used to check up the predictions of the model. The preliminary results of the optical light curve synthesis from Her X-1/HZ Her show that the model of the processing neutron star seems to be capable of describing the asymmetries and some features of the observed light curves.
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