15819864
Power Spectra of X-Ray Binaries
The interpretation of Fourier spectra in the time domain is critically examined. Power density spectra defined and calculated in the time domain are compared with Fourier spectra in the frequency domain for three different types of variability: periodic signals, Markov processes, and random shots. The power density spectra for a sample of neutron stars and black hole binaries are analyzed in both the time and the frequency domains. For broadband noise, the two kinds of power spectra in accreting neutron stars are usually consistent with each other, but the time domain power spectra for black hole candidates are significantly higher than corresponding Fourier spectra in the high-frequency range (10-1000 Hz). Comparing the two kinds of power density spectra may help to probe the intrinsic nature of timing phenomena in compact objects.
56439385
On the relation of hard X-ray peak flux and outburst waiting time in the black hole transient GX 339-4
Aims. We reinvestigate the empirical relation between the hard X-ray peak flux and the outburst waiting time found previously in the black hole transient GX 339-4. We verify the relation using the observed hard X-ray peak flux of the 2007 outburst of GX 339-4, we clarify the nature of faint flares, and we estimate the lower limit to hard X-ray peak flux of the next outburst.
118555439
Attraction-repulsion coupled and energy conserved universe
The discovery of accelerated cosmic expansion implies that, in addition to the attractive gravity of matter, there exists in our universe some other form of energy (dark energy or cosmological constant) producing a repulsive force. The natural interpretation of dark energy is the vacuum energy. However, the density of vacuum energy expected by the quantum field theory is 120 orders of magnitude larger than what is allowed by cosmological observations, which is called the cosmological constant problem and remains one of the most significant unsolved problems in fundamental physics. Here we show that the huge discrepancy can be resolved by assuming that our universe is an attraction-repulsion coupled system with energy conservation, and that the pre-inflation vacuum is in equilibrium between attraction and repulsion (in flat Minkowski spacetime, not de Sitter or anti de Sitter). The attraction-repulsion coupling picture can also easily explain why both kinds of energy in our universe have similar magnitude today, and avoid singularity problems in general relativity and cosmology.
17242777
TEMPORAL AND SPECTRAL CORRELATIONS OF CYGNUS X-1
Temporal and spectral properties of X-ray rapid variability of Cyg X-l are studied through correlation analysis in the time domain on different timescales. The correlation coefficients between the total intensity in the 2-60 keV band and the hardness ratio of the 13-60 keV to the 2-6 keV band on the timescale of similar to 1 ms are always negative in all states. For soft states, the correlation coefficients are positive on all timescales from similar to 0.01 to similar to 100 s, which is significantly different from those for transition and low states. The temporal structures in the high-energy band are narrower than those in low-energy band in quite a few cases. The delay of high-energy photons relative to low-energy ones in the X-ray variations has also been revealed by the correlation analysis. The implications of the observed temporal and spectral characteristics for the production region and mechanism of Cyg X-l X-ray variations are discussed.
16231433
Temporal and spectral properties of gamma-ray flashes
[1] The temporal and spectral properties of terrestrial gamma-ray flashes (TGFs) are studied. The delay of low energy photons relative to high energy ones in the γ-ray variations of the TGFs with high signal to noise ratio has been revealed by an approach of correlation analysis in the time domain on different time scales. The temporal structures of the TGFs in high energy band are usually narrower than that in low energy band. The spectral hardness has a general trend of decreasing with time in a flash. The observed temporal and spectral characteristics give constraints and valuable hints on the flash production mechanism.
121381895
Abnormal correlation in WMAP data: parity violation or data flaw?
The cosmic microwave background (CMB) temperature maps and the corresponding results published by the Wilkinson Microwave Anisotropy Probe (WMAP) team are the basis of precision cosmology. However, in our previous work, they have been questioned: it is discovered that the WMAP CMB temperatures are correlated with the number of observations (N-obs) (Li et al 2009 Mon. Not. R. Astron. Soc. 398 47). We have repeated this finding with a much simpler method and found more interesting attributes of the temperature-N-obs correlation. What is more, with our method, we have also found significant correlations between the CMB intensity and polarization components. With these results, either the law of parity conservation may be violated in the early universe or there may be a flaw in the WMAP data.
122803437
Effect of calibration errors on Bayesian parameter estimation for gravitational wave signals from inspiral binary systems in the advanced detectors era: Further investigations
By 2015, the advanced versions of the gravitational wave detectors Virgo and LIGO will be online. They will collect data in coincidence with enough sensitivity to potentially deliver multiple detections of gravitational waves from inspirals of compact-object binaries. In a previous work, we have studied the effects introduced in the estimation of the physical parameters of the source by uncertainties in the calibration of the interferometers. Our bias estimator for parameter errors introduced by calibration uncertainties consisted of two terms: A genuine bias due to the calibration errors, and a contribution coming from the limited number of samples used to explore the parameter space. In this article, we have focused on this second term, and we have shown how it is smaller than the former (about 10 times smaller), and how it decreases as the signal-to-noise ratio increases.
59492998
Sensitivity studies for third-generation gravitational wave observatories
Advanced gravitational wave detectors, currently under construction, are expected to directly observe gravitational wave signals of astrophysical origin. The Einstein Telescope (ET), a third-generation gravitational wave detector, has been proposed in order to fully open up the emerging field of gravitational wave astronomy. In this paper we describe sensitivity models for ET and investigate potential limits imposed by fundamental noise sources. A special focus is set on evaluating the frequency band below 10 Hz where a complex mixture of seismic, gravity gradient, suspension thermal and radiation pressure noise dominates. We develop the most accurate sensitivity model, referred to as ET-D, for a third-generation detector so far, including the most relevant fundamental noise contributions.
118385730
Testing general relativity using gravitational waves from binary neutron stars: Effect of spins
We present a Bayesian data analysis pipeline for testing GR using gravitational wave signals from coalescing compact binaries, and in particular binary neutron stars. In this study, we investigate its performance when sources with spins are taken into account.
1506194
TIGER: A data analysis pipeline for testing the strong-field dynamics of general relativity with gravitational wave signals from coalescing compact binaries
The direct detection of gravitational waves with upcoming second-generation gravitational wave observatories such as Advanced LIGO and Advanced Virgo will allow us to probe the genuinely strong-field dynamics of general relativity (GR) for the first time. We have developed a data analysis pipeline called TIGER (test infrastructure for general relativity), which uses signals from compact binary coalescences to perform a model-independent test of GR. In this paper we focus on signals from coalescing binary neutron stars, for which sufficiently accurate waveform models are already available which can be generated fast enough on a computer that they can be used in Bayesian inference. By performing numerical experiments in stationary, Gaussian noise, we show that for such systems, TIGER is robust against a number of unmodeled fundamental, astrophysical, and instrumental effects, such as differences between waveform approximants, a limited number of post-Newtonian phase contributions being known, the effects of neutron star tidal deformability on the orbital motion, neutron star spins, and instrumental calibration errors.
23581346
Demonstrating the feasibility of probing the neutron-star equation of state with second-generation gravitational-wave detectors.
Fisher matrix and related studies have suggested that, with second-generation gravitational-wave detectors, it may be possible to infer the equation of state of neutron stars using tidal effects in a binary inspiral. Here, we present the first fully Bayesian investigation of this problem. We simulate a realistic data analysis setting by performing a series of numerical experiments of binary neutron-star signals hidden in detector noise, assuming the projected final design sensitivity of the Advanced LIGO-Virgo network. With an astrophysical distribution of events (in particular, uniform in comoving volume), we find that only a few tens of detections will be required to arrive at strong constraints, even for some of the softest equations of state in the literature. Thus, direct gravitational-wave detection will provide a unique probe of neutron-star structure.