摘要:

TheRossi X‐ray Timing Explorer(RXTE) is an immensely successful mission of exploration and discovery. It has discovered a wealth of rapid X‐ray variability phenomena that can be used to address fundamental questions concerning the properties of dense matter and strong gravitational fields as well as important astrophysical questions. It has answered many questions and is likely to answer many more, but to follow up fully on the major discoveriesRXTEhas made will require a new X‐ray timing mission with greater capabilities. This introduction to the present volume describes briefly the advantages of X‐ray timing measurements for determining the properties of dense matter and strong gravitational fields, indicates some of the key scientific questions that can be addressed using X‐ray timing, and summarizes selected achievements of theRXTEmission. It concludes by citing some of the scientific capabilities a proposed follow‐on mission will need in order to be successful. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1780991

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

X‐ray QPOs from black hole binary systems provide specialized and extraordinary tools for black‐hole astrophysics. Low‐frequency QPOs (LFQPOs; 0.1–30 Hz) help us to distinguish black hole spectral states, which are now understood in terms of radiation dominance by either the accretion disk, a jet, or a compact high‐energy corona. LFQPOs can be remarkably strong (rms> 20&percent; at 2–30 keV) and coherent (Q> 10) in the “steep power‐law” state, and this imposes first‐order requirements for physical models for the compact corona that powers this state. Strong LFQPOs can also be seen in the hard state (radio‐loud, steady jet), particularly when the energy spectrum shows a mixture of thermal and hard power‐law components. In several sources, correlations have been found between LFQPO frequency and either the integrated thermal flux or the power‐law spectral index. This provides further evidence that LFQPO oscillations are tied to the energy coupling between the disk and either the jet or the compact corona.High‐frequency QPOs (HFQPOs; 40–450 Hz) are transient and subtle (rms amplitudes near 1&percent;), and most detections occur in the steep power‐law state. Three (possibly four) sources exhibit HFQPOs that primarily represent a pair of commensurate frequencies in a 3:2 ratio, with detections that cover a wide range in luminosity. Furthermore, the three pairs of QPOs appear to represent fixed frequency systems that scale inversely with black hole mass. These results provide strong encouragement to investigate HFQPOs as some type of resonance oscillation rooted in general relativity. A successful determination of the correct oscillation mechanism would yield invaluable measurement constraints on black hole mass and spin. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1780992

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

In all the microquasars with two hHz QPOs, the ratio of the frequencies is 3:2, supporting our suggestion that a non‐linear resonance between two modes of oscillation in the accretion disk plays a role in exciting the observed modulations of the X‐ray flux. We discuss the evidence in favor of this interpretation, and we relate the black hole spin to the frequencies expected for various types of resonances that may occur in nearly Keplerian disks in strong gravity. For those microquasars where the mass of the central X‐ray source is known, the black hole spin can be deduced from a comparison of the observed and expected frequencies. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1780993

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Fast variability studies of accreting black holes in the Galaxy offer us a unique opportunity to measure the spins of black holes and test the strong‐field behavior of general relativity. In this review, I summarize the arguments often used in attempts of measuring the spins of black holes, concentrating on their theoretical foundations. I also argue that X‐ray studies of accreting black holes will be able to provide in the future strong constraints on deviations from general relativity in the strong‐field regime. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1780994

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Observations of X‐ray emissions from binary systems have always been considered important tools to test the validity of General Relativity in strong‐field regimes. The pairs and triplets of high frequency quasi‐periodic oscillations observed in binaries containing a black hole candidate, in particular, have been proposed as a means to measure more directly the black hole properties such as its mass and spin. Numerous models have been suggested over the years to explain the QPOs and the rich phenomenology accompanying them. Many of these models rest on a number of assumptions and are at times in conflict with the most recent observations. We here propose a new, simple model in which the QPOs result from basicp‐mode oscillations of a non‐Keplerian disc of finite size. We show that within this new model all of the key properties of the QPOs:a)harmonic ratios of frequencies even as the frequencies change;b)variations in the relative strength of the frequencies with spectral energy distribution and with photon energy;c)small and systematic changes in the frequencies, can all be explained simply given a single reasonable assumption. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1780995

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

In at least two black hole binary systems, the Rossi X‐Ray Timing Explorer has detected high frequency quasi‐periodic oscillations (HFQPOs) with a 2:3 frequency commensurability. We propose a simple hot spot model to explain the positions, amplitudes, and widths of the HFQPO peaks. Using the exact geodesic equations for the Kerr metric, we calculate the trajectories of massive test particles, which are treated as isotropic, monochromatic emitters in their rest frames. By varying the hot spot parameters, we are able to explain the different features observed in “Type A” and “Type B” QPOs from XTE J1550‐564. In the context of this model, the observed power spectra allow us to infer values for the black hole mass and angular momentum, and also constrain the parameters of the model. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1780996

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

We present a scenario for the variability of the microquasar GRS 1915+105. This starts from previous works, leading to the tentative identification of the Accretion‐Ejection Instability as the source of the low‐frequency Quasi‐Periodic Oscillation of microquasars and other accreting sources. We follow the physics of this instability: its conditions (the magnetic field and geometry adapted to MHD jet models), its instability criterion, and its consequences (cooling down of the disk, heating and excitation of the corona). Comparing them to the observed properties of the source, in particular the detailed properties of its spectral states, we first derive a model for the ∼ 30 minutes cycles often exhibited by GRS 1915+105. In our model this is a limit cycle determined by the advection of poloidal magnetic flux to the inner region of the disk, and its destruction by reconnection (leading to relativistic ejections) with the magnetic flux trapped in the vicinity of the central source. We show how it leads to natural explanations for observed behaviors of GRS 1915+105, including the three basic states of Belloniet al.. We then discuss how this could be extrapolated further to understand the longer‐term variability of this and other microquasars. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1780997

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Black hole binaries are variable in timescales of range from months to milli‐seconds. The origin of this variability is still not clear, it could be due to the variation of external parameters, like mass accretion rate, instabilities in the inner regions of the accretion flow etc. Important constraints on these possibilities can be obtained from the study of the non‐linear behavior of fluctuations. We present a modified non‐linear time series analysis technique which optimizes the use of the available data and computes the correlation dimension in a non‐subjective manner. We apply this technique to the X‐ray light‐curve of the black hole system, GRS 1915+105, to show conclusively that at least for four of its twelve temporal classes, the underlying mechanism is a low order chaotic one. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1780998

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

We characterized the evolution of spectral and temporal properties of several Galactic black hole transients observed between 1996–2001 using the data from well sampled PCA observations close to the transition to the low/hard state. We showed that the changes in temporal properties are much sharper than the changes in the spectral properties, and it is much easier to identify a state transition with the temporal properties. The ratio of the power‐law flux to the total flux in the 3–25 keV band increases close to the transition, and the power‐law flux shows a sharp increase along with the changes in temporal properties during the transitions. In this work we concentrate on the decay of two recent outbursts, from 4U 1543‐47, and H1743‐322 and discuss the state transitions by tracking their daily, and sometimes hourly evolution, and interpret results based on the expectations from our earlier observations. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1780999

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

We report simultaneous optical and X‐ray observations of the black hole X‐ray binary system V4641 Sgr during early August 2003 when the source was in a state of violent, rapid outburst. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1781000

出版商:AIP    

年代:1904

数据来源: AIP