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We present a new theoretical framework for interpreting observed spectral/temporal characteristics of accreting neutron star and black hole systems as gravity wave (g-mode oscillations). This model successfully incorporates features of earlier models (published by the present authors and colleagues over the last several years) into a more general scheme that reduces in one limit to a classic treatment by Chandrasekhar, placing this paradigm in the tradition of his analysis. It goes beyond his treatment in the inclusion of radial dependence, the incorporation of MHD, and the application to X-ray timing phenomenology. The conceptual picture that goes with this idea is one in which the problem of disk accretion onto a (symmetrical) black hole is the starting point; accretion in geometries where symmetries are broken by magnetic fields is treated with extensions or perturbations to that case. Primary emphasis is on understanding QPO features and power spectrum breaks. Pairs or groups of QPOs that evolve in correlated ways are treated as splittings of eigenfrequencies in a fluid dynamics analysis rather than, say, as beat phenomena. One particular QPO is identified with the Kepler (gravitational) frequency and the other QPOs are related to that one. Because the Kepler frequency is Newtonian and not a General Relativistic effect, the entire treatment is Newtonian, but this helps explain how certain relationships appear to extend over ∼ six orders of magnitude in frequency, linking white dwarfs, neutron stars, and black holes in a single comprehensive picture. The explanatory range of the theoretical framework is considerable: it addresses the magnetic field strength and configuration near the compact object, the extension of the Keplerian disk near the central object (and the location of the transition between Keplerian and non Keplerian flow), the presence of advection flow along with disk accretion and the conditions for shock formation in the accretion flow. Successes of earlier treatments, for example fitting the correlated drifts of as many as six persistent power density spectrum features (QPOs or breaks) with minimal parametrization are retained in the new unified scheme. Presented calculations are aimed at (i) extending the explanatory range of the model, (ii) working out details and consequences of the new framework that unifies it with Chandrasekhar’s analysis, (iii) making it explicitly an MHD model and not simply hydrodynamics, and (iv) validating it with test. The goal is to have a theoretical synthesis of the existing QPO phenomenology that will serve as a starting point for future X-ray timing observations. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

“QVD” detectors are based on thermoelectric heat-to-voltage (Q→V) conversion and digital (V→D) readout. For spectroscopic applications, the theoretical performance limits are competitive with superconducting tunnel junction (STJ) detectors and transition edge sensor (TES) devices. We discuss theoretical and demonstrated timing performance of QVD detectors with different design architectures. Detectors with lanthanum-cerium hexaboride sensors can be very fast, up to 100 MHz/pixel counting rates. They can serve as focal plane detectors for X-ray timing, in situations where very large apertures are used to gather X-ray photons at high event rates. Practical implementation of thermoelectric (QVD) detectors requires cryogenic thermoelectric sensors with high figures of merit. There can be different solutions: thin films, bulk materials and “whiskers.” We are exploring all three design options and summarize progress in each area. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

The X-ray Large Array (XLA) was a concept for a very large area array of proportional counters attached to the Space Station, as the station concept existed in the 1980s and into the early 1990s. It was nominally 100 m2 of proportional counters for 0.25–25 keV which was (optionally) supplemented by a coded aperture telescope of area 1–2 m2. Although it never flew, it underwent a pre-Phase A study at NASA-MSFC and was discussed at many scientific conferences. The purpose of this presentation is to review lessons learned from the XLA experience, both good and bad. It reviews the scientific rationale and engineering issues in achieving and operating very large X-ray collecting apertures in space, with updates on those issues in the light of later developments. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

Orbital period changes are an important diagnostic for understanding low mass X-ray binary (LMXB) accretion-induced angular momentum exchange and overall system evolution. We present our most recent results for the eclipse timing of the LMXB EXO0748-676. Since its discovery in 1985 it has apparently undergone three distinct orbital period “epochs”, each characterized by a different orbital period than the previous epoch. We outline the orbital period behavior for EXO0748-676 over the past 18 years and discuss the implications of this behavior in light of current theoretical ideas for LMXB evolution. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

We report on progress in developing thick silicon detectors for X-ray and gamma-ray astronomy. Silicon detectors offer good spectroscopy at reasonably low cost and with low internal background in the energy range between 5–50 keV. This technology offers a smooth energy response and a very fast timing response for high rate applications. We are testing large area, double-sided 2mm thick detectors for applications requiring large quantities of silicon. Our current laboratory prototypes are 63 × 63 mm in area, and we will soon have detectors that are 95×95 mm in area and with thicknesses up to 3 mm. As part of our prototyping efforts, we are developing double-sided strip detectors, pixel detectors, as well as hybrid pixel/strip detectors. We present our latest laboratory results in terms of imaging and spectroscopy, as well as our progress in developing and integrating custom readout ASICs. These detectors and electronics, while not a perfect match for a next generation X-ray timing mission, form a good basis for the design of dedicated large area detectors in the 5–50 keV energy range. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

We report on long term timing observations of the 3.05 ms pulsar PSR B1821–24, made with the Proportional Counter Array (PCA) on NASA's Rossi X-ray Timing Explorer (RXTE), which have an absolute pulse time of arrival accuracy of <3.5 μs. We compare these observations to careful radio timing observations taken at Nançay Observatory and the Green Bank Telescope, which allow us to track the variable dispersion measure so that we can compensate for radio propagation effects. These data are the first high precision long term timing measurements of a millisecond pulsar in the X-ray band and demonstrate that timing of X-ray emitting MSPs in the X-ray band can be an important complement to radio timing programs. [ABSTRACT FROM AUTHOR]