摘要:

We present a study of the long‐term variability of Cyg X‐1 using data from the RXTE/ASM and the RXTE/PCA during the time between the two soft states of 1996 and 2001/2002. This period has been characterized by many short ASM flaring episodes which we have identified as “failed state transitions”. The 150 d period which has been seen before and shortly after the 1996 soft state is not obviously present in the ASM rate during most of this time. Applying selection criteria from our pointed RXTE/PCA observations to exclude the flaring episodes we show that the 150 d period can indeed still be significantly detected in the hard state. Furthermore, while the ∼420 d timescale associated with the flaring is reduced in the selected hard state count rate, it is still pronounced in the temporal evolution of the corresponding hardness ratios. The Ryle radio flux is also consistent with the 150 d period being present but distorted during this time. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1781001

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

We present high time‐resolution multicolour observations of the quiescent soft X‐ray transients V404 Cyg and XTE J1118+480 obtained with ULTRACAM. The power density spectrum (PDS) of the V404 Cyg data shows a quasi‐periodic oscillation (QPO) feature at 0.78 mHz (=21.5 min), whereas the PDS of the XTE J1118+480 data shows a break. We discuss the possible origins for the QPO feature and break‐frequency in the context of the advection‐dominated accretion flow model. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1781002

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Black hole binaries exhibit dramatic changes in their X‐ray spectral and timing properties over time, providing important clues about the physical processes that occur in these systems. Black holes and black hole candidates are prime targets forRXTEwith observational goals including the study of extreme gravitational fields and jet formation mechanisms. The great wealth of data fromRXTEhas helped us to learn about these systems as well as raising new questions about accreting black holes.RXTEobservations have allowed us to study a wide range of black hole science topics including the connection between the accretion disk and jets, the geometry of the inner accretion flow, and the physical changes that occur between spectral states. In this presentation, I discuss significant results on these topics that have been obtained for persistent and transient black holes over the past several years, and I present results from our program of X‐ray and radio observations during the decays of black hole transient outbursts. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1781003

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

I review the main theoretical conclusions from high‐energy spectral observations of Galactic Black Hole Candidate systems. With an eye towards future missions, I show how the ability to reach such conclusions depends critically on the type of spectral coverage one has available. Perhaps the most important factor in determining how well a set of observations constrains theoretical models is the range of energies that can be observed in a simultaneous manner, the wider the better. High spectral resolution observations over a narrow energy band, e.g., as provided by Chandra and eventually ASTRO E‐2, are potentially extremely interesting but not as useful as one might first think without an understanding of the underlying broad‐band continuum. A snapshot, time‐integrated spectrum that has very wide energy coverage, however, is still not sufficient to break all the current model degeneracies. The tightest model constraints instead come from combining spectral with timing information. The RXTE satellite excelled in this regard, enabling unprecedented spectral variability studies on both short and long timescales by virtue of its large collection area, broad energy response, and flexible scheduling. Future instruments, or combinations of instruments, must strive for a similar balance of timing and broad‐band spectral capabilities if they are to prove as effective as RXTE. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1781004

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

There are four major X‐ray satellites currently in operation (RXTE, Chandra, XMM‐Newton, INTEGRAL), with two more shortly to follow (Astro E II, Swift), and several very ambitious observatories in various stages of planning (Constellation‐X, MAXIM, XEUS). This very rich period of X‐ray observation is leading to great advances in our understanding of the accretion flow onto the black hole, although we are quickly learning (or perhaps better put, remembering) exactly how complicated this flow can be. This review was meant to assess future prospects for X‐ray spectroscopy of black hole binaries; however, I first look backward to the observations and theories that helped us arrive at our current ‘paradigm’. I then discuss current and near‐future spectroscopic studies, which increasingly (and very fruitfully) treat X‐ray spectroscopy as part of a larger, intimately connected picture along with radio, optical, and gamma‐ray spectroscopy. Equally importantly, and in large part thanks to the success ofRXTE, there is now a strong realization that spectral‐temporal correlations, even across wavelength bands, are crucial to our understanding of the physics of these systems. Going forward, we are well‐poised to continue to advance our knowledge via X‐ray spectroscopy, both with existing satellites that have a long lifetime ahead of them (Chandra, XMM‐Newton, INTEGRAL), and with the next generation of instruments. If there is any ‘hole’ in this bright future, it is the potential loss ofRXTE, with no designated follow‐up mission. Studies of multi‐wavelength spectral‐temporal correlations will become more difficult due to the loss of two important attributes ofRXTE: its fast timing capabilities and its extremely flexible scheduling which has made many of these studies possible. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1781005

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

RXTE/PCA observations of several black hole X‐ray binaries in the low spectral state revealed a tight correlation between spectral parameters and characteristic frequencies of variability of X‐ray flux. In particular, the amplitude of reflection increases and the slope of Comptonized radiation steepens as the noise frequencies increase. The data also suggest that there is a correlated increase of the width of the Fe fluorescent line, probably related to the Doppler broadening of the reflection features. Moreover, the width of the line seems to follow&Dgr;E/E ∝ vQPO1/3law. If confirmed with higher energy resolution observations, this result will have significant impact on the models of the accretion flow and on our understanding of the nature of characteristic frequencies of variability in X‐ray binaries. In particular, it will lend support to the truncated disk picture, confirming that the spectral variations are indeed related to changes of the position of the inner disk boundary and that characteristic variability frequencies are proportional to the Keplerian frequency at the inner boundary of the accretion disk. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1781006

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

We propose a jet model for the low/hard state of galactic black‐hole X‐ray sources which explains a) the X‐ray spectra, b) the time‐lag spectra, and c) the increase of the amplitude of variabilty (quasiperiodic oscillations and high frequency) with increasing photon number. The model (in its simplest form) assumes that i) there is a uniform magnetic field along the axis of the jet, ii) the electron density in the jet is inversely proportional to the distance from the black hole, and iii) the jet is hotter near its center than at its periphery. We have performed Monte Carlo simulations of Compton upscattering of soft photons from the accretion disk and have found power‐law high‐energy spectra with photon index in the range 1.5 – 2, power‐law time lags versus Fourier frequency with index 0.7, and an increase of the rms amplitude of variability with photon energy as it has been observed. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1781007

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Long‐term monitoring of 1E 1740.7‐2942 and GRS 1758‐258 has revealed behavior very different from the “prototype” black‐hole candidate Cyg X‐1. In these two sources, as we have previously reported, the softest spectra are seen while the luminosity is dropping, rather than when it is highest, as in Cyg X‐1. The difference may be related to the accretion geometry (wind‐fed vs. disk‐fed) via the long viscous time scale for the propagation of changes through a large accretion disk.We now add an additional piece of information to the analysis: the total rms fast variability in each observation. We find that this parameter correlates better with the spectral index than either the luminosity or its derivative. The correlation has no observable lag and is particularly striking in GRS 1758‐258. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1781008

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

We present results from detailed spectral analyses of 43 RXTE observations of GRO J1655‐40 made throughout 1996. Spectra taken over 27 days separated by about one week each allow us to determine 3–200 keV continuum and line variability during the thermally dominated and steep power‐law states seen. Inferred effective radii for maximum disk emission are consistently below 6 gravitational radii, confirming the Kerr nature of the black hole. The broad iron line is modeled by a broad emission line and an absorption edge at ∼6.7 keV. We discuss the variation in line and continuum parameters, and suggest the inner portion of the accretion disk is warped and hot. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1781009

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Cygnus X‐3 is an unusual object. From the time of its discovery over 30 years ago, despite more and more sophisticated studies, its behavior still brings more questions than answers. We have collected all the public Cyg X‐3 RXTE data and divided it into four groups in respect of the shape of the PCA/HEXTE spectrum. The two out of four groups are distinctly different from the widely known spectral states: hard and soft. Furthermore, using XSTAR and on the basis of the BeppoSAX data, attempts have been made to solve the problem of the strong and complex neutral and ionized absorption, referring to the system itself, its close vicinity and the interstellar medium across Galactic plane. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1781010

出版商:AIP    

年代:1904

数据来源: AIP