Other
Scientific paper
Jan 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992phdt........23s&link_type=abstract
Ph.D. Thesis Rochester Univ., NY.
Other
Light Curve, Neutron Stars, Periodic Variations, Polar Caps, Radio Emission, Stellar Oscillations, Stellar Radiation, X Ray Sources, Micropulsations, Particle Trajectories, Photons, Pulsars, Stellar Models, Stellar Rotation, X Rays
Scientific paper
To investigate detecting and identifying neutron star oscillations in x ray sources, a technique for computing the light curves produced from polar cap hotspots on rotating, oscillating neutron stars is developed. The calculations include the effects of general relativity on the photon trajectories and allow for anisotropic beaming of radiation from the polar caps. A simple model, based on stellar oscillation, for the subpulse drift phenomenon observed in some radio pulsars is also described. Simulations of x ray observations of both x ray bursters and x ray pulsars using parameters appropriate to XTE and AXAF are investigated in order to assess the likelihood of detecting neutron star oscillations in these sources. To examine theoretically whether or not oscillations of neutron stars can modulate pulsar radio emission, a cylindrical model for the polar cap region of pulsars is investigated. An argument based on relativistic beaming allows estimation of the surface oscillation amplitude required to produce potentially observable variations in the beaming angle. For this model, short period modes require smaller surface displacements, and therefore less energy, to excite potentially observable variations. To investigate the hypothesis that neutron star oscillations may be present in the radio emission from pulsars, radio pulsar data are analyzed for the presence of coherent periodicities. The analysis technique described here allows measurement of the coherence properties of pulsar signals. To test this method and interpret results from pulsar data several simulated pulsar models are constructed and analyzed. An analysis of 2000 consecutive pulses from PSR 2016 + 28 yields the following conclusions: The micropulse coherence time at 430 MHz is much less than the spin period of this object. This result could be consistent with a coherent model if the random phase jitter in such a model were greater than or equal to 35 percent of the micropulse quasiperiodicity. The subpulse separation, P2 approximately equals 10 ms, is coherent across four to five pulse periods, suggesting a higher Q-value for this process than for the micropulses. This coherence level is reasonably consistent with a model of subpulse drift that allows for random variation about some mean drift rate. Additional analysis of data from two other pulsars, PSR 1133 + 16 and PSR 0950 + 08, reveals no evidence for coherent oscillations in these objects as well.
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