Spectral/timing evolution of black-hole binaries

I briefly outline the state-paradigm that has emerged from the study of black-hole binaries with RossiXTE. This is the starting point of a number of studies that address the connection between accretion and jet ejection and the physical nature of the hard spectral components in these systems.Comment: 4 pages, 2 figures.To appear in Proceedings of "X-ray Astronomy 2009: Present Status, Multi-Wavelength Approach and Future Perspectives", Bologna, Italy, September 7-11, 2009, AIP, eds. A. Comastri, M. Cappi, and L. Angelin

LOFT: the Large Observatory For X-ray Timing

LOFT, the large observatory for X-ray timing, is a new mission concept competing with other four candidates for a launch opportunity in 2022-2024. LOFT will be performing high-time resolution X-ray observations of compact objects, combining for the first time an unprecedented large collecting area for X-ray photons and a spectral resolution approaching that of CCD-based X-ray instruments (down to 200 eV FWHM at 6 keV). The operating energy range is 2-80 keV. The main science goals of LOFT are the measurement of the neutron stars equation of states and the test of General Relativity in the strong field regime. The breakthrough capabilities of the instruments on-board LOFT will permit to open also new discovery windows for a wide range of Galactic and extragalactic X-ray sources. In this contribution, we provide a general description of the mission concept and summarize its main scientific capabilitie

Black-hole binaries: life begins at 40 keV

In the study of black-hole transients, an important problem that still needs to be answered is how the high-energy part of the spectrum evolves from the low-hard to the high-soft state, given that they have very different properties. Recent results obtained with RXTE and INTEGRAL have given inconsistent results. With RXTE, we have found that the high-energy cutoff in GX 339-4 during the transition first decreases (during the low-hard state), then increases again across the Hard-Intermediate state, to become unmeasurable in the soft states (possibly because of statistical limitations). We show Simbol-X will be able to determine the spectral shape with superb accuracy. As the high-energy part of the spectrum is relatively less known than the one below 20 keV, Simbol-X will provide important results that will help out understanding of the extreme physical conditions in the vicinity of a stellar-mass black hole.Comment: Proc. "Simbol-X: Focusing on the Hard X-Ray Universe", Paris, 2-5 Dec. 2008, ed. J. Rodriguez and P. Ferrando; 4 pages, 3 figure

High-Frequency Variabilityin Neutron-Star Low-Mass X-rayBinaries

Binary systems with a neutron-star primary accreting from a companion star display variability in the X-ray band on time scales ranging from years to milliseconds. With frequencies of up to ∼1300 Hz, the kilohertz quasi-periodic oscillations (kHz QPOs) represent the fastest variability observed from any astronomical object. The sub-millisecond time scale of this variability implies that the kHz QPOs are produced in the accretion flow very close to the surface of the neutron star, providing a unique view of the dynamics of matter under the influence of some of the strongest gravitational fields in the Universe. This offers the possibility to probe some of the most extreme predictions of General Relativity, such as dragging of inertial frames and periastron precession at rates that are 16 orders of magnitude faster than those observed in the solar system and, ultimately, the existence of a minimum distance at which a stable orbit around a compact object is possible. Here we review the last 20 years of research on kHz QPOs, and we discuss the prospects for future developments in this field.<br/