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X-ray Emission from Low Mass Binary Systems X-ray time-series and spectra of two LMXRBs are presented. The data are from the the well-known X-ray burster MXB1636-536 and the dipping source 4U1624-49. In the case of MXB1636-536, a simultaneous optical observation is also presented. The 2-20 keV persistent X-ray emission from MXB1636-536 is found to show both positive and negative hardness-flux correlations and to vary by a factor of &sim; 2 on timescales of hours. The persistent spectrum is best described by a power law with high energy cut-off, indicative that Comptonization dominates the spectral formation in the inner accretion disk. The temperature, optical depth and Compton y parameter of the Comptonizing plasma are derived; the Compton y parameter shows that the spectrum is consistent with unsaturated Comptonization. The negative hardness-flux correlation is explained in terms of the Compton cooling of a hot neutron star corona as a result of an increase in accretion rate. It is notable that a negative hardness-flux correlation and a power law spectrum is in direct conflict with previous observations of this source. Thirteen X-ray bursts, exhibiting a wide variety of profile, were also observed from MXB1636-536. The peak burst flux and burst fluence varied by a factor of 6 and 5 respectively. The burst sample may be divided into two distinct classes: those with fast rise and high peak intensity (strong) and those with slow rise and low peak intensity (weak). Moreover, the strong bursts are 'super-Eddington' and one of the weak bursts is unusual in that it is double-peaked in both the X-ray and bolometric burst profiles. The observed burst properties are discussed within the framework of the current thermonuclear flash models and other physical scenarios. One of the bursts, observed simultaneously in both the X-ray and optical wavebands, is used to determine the possible locality of the reprocessing region in the accretion disk. 4U1624-49 reveals a pattern of dips in the 1-10 keV X-ray light-curve which repeat with a period of ~21 hours. This is almost certainly the binary period of the system, making it one of the longest binary periods amongst LMXRBs. The &sim;25% residual flux can be associated with a physically extended emission component whereas the dips are associated with the intermittent obscuration of a compact component by material in the line-of-sight. The spectral changes occuring within the dips are complex and indicate energy-independent reductions in flux and substantial increases in absorption. The dips cannot be explained by a bulge at the outer disk edge (at the point of impact with the incoming stream) obscuring the central X-ray source. Assuming the primary of 4U1624-49 is a 1.4M? neutron star, the companion is likely to be an evolved star with a mass < 3M? and radius < 2.75R?. The orbital inclination is found to be within the range predicted by the FKL model for 'pure dippers' i.e. 60° < I < 75°.

The high-mass X-ray binary SMC X-1 has been observed during the interval 1986-1989 at a threshold γ-ray energy of 0.4 TeV using the University of Durham Mark III air Cerenkov telescope at Narrabri. The Cerenkov arrival time series recorded during these observations have been tested for periodicity at the contemporary pulse period of the SMC X-1 X-ray pulsar. This period analysis was performed using a new technique - introduced in the present work - which is designed for TeV γ-ray source candidates in binary systems and which simultaneously seeks evidence for pulsed TeV γ-ray emission and information on the location of the emission site within the binary. Results are also presented from the period analysis of data accumulated at Narrabri during observations of the low-mass X-ray binaries X0021.8-7221 (in the globular cluster 47 Tucanae) and GX 1+4. X-ray binaries as a class of TeV γ-ray source are considered and their properties compared. Previous models which invoke the interaction of beams of high-energy particles with material within the environment of a binary system are discussed. One of these models is adapted in the present work in order to propose a simple explanation of the narrow TeV 7-ray orbital light curve observed for the high-mass binary Centaurus X-3. The new model accounts for the γ-ray emission from Cen X-3 in terms of the collisions of ultrarelativistic protons with an accretion wake trailing the X-ray pulsar. This model, which incorporates the steering of charged particles in the magnetosphere of the massive primary star, is also applied to the Vela X-1 binary in order to investigate claims that TeV γ-ray outbursts observed during X-ray eclipse arise at particle collisions with the limb of the supergiant companion.

Thesis (M. Phil.)--University of Hong Kong, 1994. / Includes bibliographical references.

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Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Physics, 1982. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE / Bibliography: leaves 29-30. / by Rupert LaWendell Seals. / M.S.

published_or_final_version / Physics / Master / Master of Philosophy

Thesis (Ph. D.)--University of Hawaii at Manoa, 2001. / Includes bibliographical references (leaves 180-195). Also available on microfiche.

published_or_final_version / abstract / Physics / Master / Master of Philosophy