摘要:

X‐ray pulsar emission is caused by mass infalling onto the magnetic polar regions of neutron stars. The collision stopping length caused by nuclear and coulomb collisions is too large for a standing shock to form above a neutron star surface. We show that collisionless excitation of plasma waves can probably produce a stopping length sufficiently small for such a shock to form. We also describe hydrodynamic models of mass infall under steady state conditions. ©1994 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.45929

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

The rapid x‐ray variability of black hole candidates and neutron stars with high, low, and very low magnetic fields is compared. Similarities in the properties of the variability between source types suggest that similar physical mechanisms underly some power spectral components seen in common in neutron stars with various magnetic‐field strengths and black hole candidates. Other components appear to be unique for magnetized neutron stars. Suggestions are made for the sites of origin and generation mechanisms of these power spectral components. ©1994 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.45930

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

I briefly review the theory of tidal instabilities in the accretion disks of close binaries. Superhump‐type disturbances result from the presence of the 3:1 resonance inside the disc, requiring mass ratiosq=M2/M1<qcrit&bartil;0.25–0.33. Tidal instabilities seem to occur in all cataclysmic variables which satisfy this condition. A number of low‐mass x‐ray binaries also exhibit similar phenomena; their presence offers a new way of obtaining information about the component masses of these systems. This may be particularly useful for suspected black‐hole binaries. The period excess associated with superhump phenomena may be rather small in LMXBs with very small mass ratios, and other signatures of tidal instabilities, such as possible vertical disc structure effects, should be looked for. ©1994 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.45931

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

X‐ray time series data from the 4.8‐second binary pulsar Cen X‐3 observed with Ginga are analyzed. We study the fractal dimension of x‐ray intensity of the total 1.7∼37 keV energy band. The fractal dimensions of the temporal behavior on time scales ≥4.8 seconds are comparatively large. It implies that the source varies with small size perturbations compared with the scale of the system. The effect of noise on the fractal dimension is estimated briefly. It is mentioned that there exists a low dimensional motion with the time scale of 500 s. ©1994 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.45932

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

In this paper I review the observational evidence for long‐term superorbital periodicities and quasi‐periodic phenomena in x‐ray binaries with time scales of ∼30 days to ∼10 years, and discuss their physical interpretation. Superorbital periods may be directly measured from long‐term x‐ray monitoring, inferred by spectroscopic or ‘‘circumstantial’’ evidence, or (perhaps) deduced from changes in the binary orbital period. Possible causes of these periods are: precision processes within the binary; irradiation of the companion by the compact object and/or stellar activity in the companion star; or the presence in the system of a third body, making the source a hierarchical triple. Each of these processes has its own implications for binary evolution. ©1994 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.45933

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

The increase in the orbital period of X 1822–371 with a timescale of 3×106yrs is confirmed by a new ROSAT observation. In contrast to some other LMXBs, a simple quadratic ephemeris remains a good fit to the eclipse timings. ©1994 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.46038

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

We found flaring branch behavior in the Z‐source GX 5−1. This source also shows secular variations in the position of the ‘‘Z’’ curve in its x‐ray color‐color and hardness‐intensity diagram. We report the detection of a new burst in GX 17+2. This burst and previous reported bursts with EXOSAT occurred when GX 17+2 was in the normal branch. ©1994 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.45934

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Progress is reported on an ongoing times series analysis of the Rapid Burster. ©1994 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.45936

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

This paper presents a simple kinematic model of the so‐called ‘‘very high state’’ of black hole candidates, during which several QPO observations have been made. The model is based upon the viscous and thermal instabilities that are believed to be present in accretion disks. In this model, the very high state is a transition phase between the high (thermal, quiescent) state and low (power law, highly variable) state that is characterized by a quasi‐stable disk oscillating on the local instability timescales. The disk can be stablized by a hot wind that could feed a Compton cloud, which in turn could produce the hard tail in the observed x‐ray spectra. The model is able to reproduce both the overall shape and the amplitude of the power spectral density and the observed frequency dependent lags between the hard and soft x‐rays. In addition, the required energetics of the hot wind is shown to be consistent with the energy required to feed the hypothesized Compton cloud. Specific comparisons between the model and data taken during the very high state of GX339‐4 are made. ©1994 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.45937

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

The vertical oscillation of an accretion disk surrounding a neutron star is studied by using the OPAL opacities. We have found that the vertical structure of the model disk is vibrationally unstable when we use new opacities instead of the Los Alamos opacities. ©1994 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.45938

出版商:AIP    

年代:1994

数据来源: AIP