Developments of EXITE2 and timing analysis of ultra-compact X-ray binaries

The second generation Energetic X-ray Imaging Telescope Experiment (EXITE2) is designed to image (22 arcmin resolution) and measure spectra of cosmic X-ray sources in the 20–600 keV band from a high altitude scientific balloon. I describe the continued development of the EXITE2 imaging phoswich (NaI(Tl)/CsI(Na)) detector and its pulse-shape discriminator (PSD) as well as tagged calibration source (Am-241) system. A low gain imaging readout and event blanking system has been implemented with the PMT dynodes to minimize effects of cosmic ray saturation and afterglow. A new method for measuring the data throughput caused by detector dead time and limited telemetry rate by low frequency, artificial snap-shot events has been developed. The data compression and its data analysis method have been tested and applied to the observations. A developmental pulse-height-independent PSD system is also discussed in this thesis. EXITE2 has been flown three times between 1997 and 2001. I describe the image analysis methods and the detector laboratory/flight performances, and include discussions of sensitivity loss of the phoswich detector during the flight due to the residual glows of CsI(Na) from cosmic rays. The observation results of the Crab nebula, the black hole binary Cyg X-1 and the 3C273/GRS 1227+025 from EXITE2 flights in 1997, 2000, and 2001 are reported. The timing analysis of RXTE data on two ultra-compact low-mass X-ray binaries (LMXBs), X 1916-053 and 4U 1820-30, are presented in the last two chapters. I report the discoveries of the 3.9d period of X-ray dip shape modulation, X-ray/optical dip period stabilities and the X-ray burst-dip timing correlation for the X 1916-053 system. The SU UMa and triple models are discussed by way of explaining the timing phenomena of X 1916-053. For the 4U 1820-30 system, I update the quadratic ephemeris and period derivative of the 11-minute orbital modulation and search the possible side bands predicted by a triple model. The RXTE/ASM ephemeris is extended by analyzing all historical data to yield a period of 171.033 ± 0.326 days with no evidence for period change. All reported X-ray burst activities are confined to within ±23d of the predicted minima. This stable long-term modulation is consistent with 4U 1820-30 being a hierarchical triple system with a ∼1.1d period companion.