摘要:

Regular monitoring of the SMC with RXTE has revealed a huge number of X‐ray pulsars. Together with discoveries from other satellites at least 45 SMC pulsars are now known. One of these sources, a pulsar with a period of approximately 7.8 seconds, was first detected in early 2002 and since discovery it has been found to be in outburst nine times. The outburst pattern clearly shows a period of 45.1 ± 0.4 d which is thought to be the orbital period of this system. Candidate outburst periods have also been obtained for nine other pulsars and continued monitoring will enable us to confirm these. This large number of pulsars, all located at approximately the same distance, enables a wealth of comparative studies. In addition, the large number of pulsars found (which vastly exceeds the number expected simply by scaling the relative mass of the SMC and the Galaxy) reveals the recent star formation history of the SMC which has been influenced by encounters with both the LMC and the Galaxy. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1781051

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Quasi‐Periodic phenomena has been seen in several types of long‐period (P > 50 ms) accreting pulsars, including the Be/X‐ray transients and the super‐giant disk‐fed systems. It has also been seen in the ultra‐compact LMXB system 4U 1626‐67, and the unique LMXB transient GRO J1744‐28. I summarize these observations, and discuss what can be learned from observing with an instrument more sensitive than RXTE/PCA. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1781052

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

We report timing and spectral properties of the transient X‐ray pulsar EXO 053109‐6609.2 using observations carried out with ASCA, BeppoSAX, and XMM‐Newton observatories. Pulse period measurements of the source show a monotonic spin‐up trend since 1996. The pulse profile is found to have a strong luminosity dependence, a single peaked profile at low luminosity that changes to a double peaked profile at high luminosity. The X‐ray spectrum is described by a simple power‐law model with photon index in the range of 0.2–0.8. A soft excess over the power‐law continuum is also detected from XMM‐Newton observation. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1781053

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

PSR J0205+6449 is a young pulsar in the Crab‐like pulsar wind nebula 3C 58 which is thought to be a result of the historical supernova SN1181 CE. The 65.7‐ms pulsar is the second most energetic of the known Galactic pulsars and has been shown to be remarkably cool for its age, implying non‐standard cooling processes in the neutron star core. We report onRXTEtiming observations taken during AO7 and supplemented by monthly radio observations of the pulsar made with the Green Bank Telescope (GBT). The total duration covered with the timing solutions is 450 days. We measure very high levels of timing noise from the source and find evidence for a “giant” glitch of magnitude &Dgr;v/v∼ 1 × 10−6that occurred in 2002 October. We have also measured the phase‐resolved spectra of the pulsations and find them to be surprisingly hard, with photon indices&Ggr; = 0.84−0.15+0.06for the main pulse and&Ggr; = 1.0−0.3+0.4for the interpulse assuming an absorbed power‐law model. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1781054

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Before the launch of the Rossi X‐ray Timing Explorer (RXTE) it was recognized that neutron star accretion disks could extend inward to very near the neutron star surface, and thus be governed by millisecond timescales. Previous missions lacked the sensitivity to detect them. The kilohertz quasi‐periodic oscillations (QPO) thatRXTEdiscovered are often, but not always, evident in the X‐ray flux. In 8 yearsRXTEhas found kilohertz signals in about a fourth of 100 low‐mass X‐ray binaries (LMXB) containing neutron stars. The observed power spectra have simple dominant features, the two kilohertz oscillations, a low frequency oscillation, and band‐limited white noise. They vary systematically with changes in other source properties and offer the possibility of comparison with model predictions. New information from the millisecond pulsars resolves some questions about the relations of the QPO and the spin. Coherence, energy spectrum and time lag measurements have indicated systematic behaviors, which should constrain mechanisms. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1781055

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

The high time resolution and large area of the Rossi X‐ray Timing Explorer have been essential in the detection and characterization of high‐frequency quasi‐periodic variability in the flux from neutron stars in low‐mass X‐ray binaries. An unknown phenomenon prior to RXTE, kilohertz quasi‐periodic oscillations (QPOs) have now been detected from more than twenty systems. Their high frequencies (up to 1330 Hz) imply that they are generated close to the neutron star, where general relativistic effects are expected to play an important role. I summarize current models for the kilohertz QPO phenomenon. In particular, I show that there is a significant domain of agreement among the models that can be used to constrain neutron star structure and look for signatures of highly curved spacetime in the properties of the QPOs. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1781056

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Millisecond X‐ray time variability studies of accreting low‐magnetic‐field neutron stars in X‐ray binaries probe the motion of matter in regions of strong gravity. In these regions, general relativity (GR) is no longer a small correction to the classical laws of motion, but instead dominates the dynamics: we are studying motion in strongly curved spacetime. Such millisecond X‐ray variability studies can therefore provide unique tests of GR in the strong‐field regime. The same studies also constrain neutron‐star parameters such as stellar mass and radius, and thereby the equation of state (EOS) of ultradense matter. By comparing neutron star and black hole phenomenology the models can be constrained in unique ways. I discuss the prospects for mapping out space‐time near accreting stellar‐mass compact objects, and measuring the EOS of dense matter, through millisecond timing, particularly with an eye towards future missions. The key to further progress is timing sensitivity, and the overwhelming consideration for timing sensitivity is collecting area: contrary to most applications, the signal‐to‐noise ratio for the aperiodic timing phenomena produced by accretion flows increasesproportionallywith count rate rather than as the square root of it. A ten times larger instrument turns 1&sgr; effects into 10&sgr; effects (or does as well in 1&percent; of the time). With the Rossi X‐ray Timing Explorer (RXTE), using 0.6 m2collecting area, we have found several timing diagnostics from the accretion flow in the strong‐gravity region around neutron stars and black holes. Next‐generation timing instruments, larger in area by an order of magnitude and with enhanced spectral capabilities, are expected to turn thesediagnosticsof GR into truetestsof GR. They are also expected to put strong constraints on neutron‐star structure, and thereby on the EOS of supranuclear density matter. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1781057

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

The presence of a kHz frequency in LMXBs has been expected from scaling laws, by analogy with the QPO phenomenon in HMXB X‐ray pulsars. Interpretation of the two kHz frequencies, observed in accreting neutron stars, in terms of non‐linear resonance in strong‐field gravity led to the prediction of twin QPOs in black hole systems, in a definite frequency ratio (such as 2/3). The imprint of a subharmonic of the 401 Hz rotation rate in the frequencies of the QPOs detected in the accreting millisecond pulsar is at once a signature of non‐linear resonance and of coupling between accretion disk modes and the neutron star spin. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1781058

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

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

ISSN:0094-243X    

DOI:10.1063/1.1781059

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

We have investigated the X‐ray variability of Sco X‐1 on its normal branch when several simultaneous noise components and quasi‐periodic oscillations (QPOs) are observed with theRossiX‐ray Timing Explorer (RXTE). The upper kHz QPO frequency is anti‐correlated with the X‐ray flux on the time scales of the very low frequency noise (VLFN) and the normal branch oscillation (NBO), while the lower kHz QPO strength seems anti‐correlated with the NBO flux, opposite to that of the horizontal branch oscillation (HBO). We summarize the overall picture of decomposing the X‐ray variability of Sco X‐1 on its normal branch into these noise components and QPOs, and discuss the consequences for the X‐ray variability models. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1781060

出版商:AIP    

年代:1904

数据来源: AIP