118957383
X-Ray Spectral Variability in the Initial Rise of XTE J1550–564
X-ray variability of the microquasar XTE J1550 - 564 is studied with time-domain techniques using data from an RXTE PCA observation on 1998 September 8. The 2-60 keV average shot profile is obtained by superposing shots with 1 ms time binning after aligning their peaks. The spectral behavior during the averaged shot exhibits prominent differences from that previously observed in Cyg X-1. The 13-60 keV/ 2-13 keV and 16-60 keV/ 13-16 keV hardness ratios during a shot are lower and higher, respectively, than those for steady emission. The correlation coefficients between intensity and 13-60 keV/ 2-13 keV and 16-60 keV/ 13-16 keV hardness ratios are also negative and positive, respectively. These results indicate that the physical processes at work in the low state of XTE J1550 - 564 may be different from those in Cyg X-1.
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.
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.
16484577
Evolution of Hard X-Ray Spectra along the Branches in Circinus X-1
Using the data from the Proportional Counter Array and the High-Energy X-Ray Timing Experiment on board the Rossi X-Ray Timing Explorer satellite, we investigate the evolution of the 3-200 keV spectra of the peculiar low-mass X-ray binary Circinus X-1 along the branches on its hardness-intensity diagram (HID) from the vertical horizontal branch, through the horizontal horizontal branch and normal branch, to the flaring branch. We detect a power-law hard component in the spectra. It is found that the derived photon indices (Γ) of the power-law hard component are correlated with the position on the HID. The power-law component dominates the X-ray emission of Cir X-1 in the energy band higher than ~20 keV. The fluxes of the power-law component are compared with those of the bremsstrahlung component in the spectra. A possible origin of the power-law hard component is 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.
118632100
Determination of Dark Energy by the Einstein Telescope: Comparing with CMB, BAO and SNIa Observations
A design study is currently in progress for a third-generation gravitational-wave (GW) detector called the Einstein Telescope (ET). An important kind of source for ET will be the inspiral and merger of binary neutron stars up to $z\ensuremath{\sim}2$. If binary neutron star mergers are the progenitors of short-hard $\ensuremath{\gamma}$-ray bursts, then some fraction of them will be seen both electromagnetically and through GW, so that the luminosity distance and the redshift of the source can be determined separately. An important property of these ``standard sirens'' is that they are self-calibrating: the luminosity distance can be inferred directly from the GW signal, with no need for a cosmic distance ladder. Thus, standard sirens will provide a powerful independent check of the $\ensuremath{\Lambda}\mathrm{CDM}$ model. In previous work, estimates were made of how well ET would be able to measure a subset of the cosmological parameters (such as the dark energy parameter ${w}_{0}$) it will have access to, assuming that the others had been determined to great accuracy by alternative means. Here we perform a more careful analysis by explicitly using the potential Planck cosmic microwave background data as prior information for these other parameters. We find that ET will be able to constrain ${w}_{0}$ and ${w}_{a}$ with accuracies $\ensuremath{\Delta}{w}_{0}=0.099$ and $\ensuremath{\Delta}{w}_{a}=0.302$, respectively. These results are compared with projected accuracies for the JDEM baryon acoustic oscillations project and the SNAP type Ia supernovae observations.
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.
118457757
Towards a generic test of the strong field dynamics of general relativity using compact binary coalescence
Coalescences of binary neutron stars and/or black holes are amongst the most likely gravitational-wave signals to be observed in ground based interferometric detectors. Apart from the astrophysical importance of their detection, they will also provide us with our very first empirical access to the genuinely strong-field dynamics of General Relativity (GR). We present a new framework based on Bayesian model selection aimed at detecting deviations from GR, subject to the constraints of the Advanced Virgo and LIGO detectors. The method tests the consistency of coefficients appearing in the waveform with the predictions made by GR, without relying on any specific alternative theory of gravity. The framework is suitable for low signal-to-noise ratio events through the construction of multiple subtests, most of which involve only a limited number of coefficients. It also naturally allows for the combination of information from multiple sources to increase one's confidence in GR or a violation thereof. We expect it to be capable of finding a wide range of possible deviations from GR, including ones which in principle cannot be accommodated by the model waveforms, on condition that the induced change in phase at frequencies where the detectors are the most sensitive is comparable to the effect of a few percent change in one or more of the low-order post-Newtonian phase coefficients. In principle the framework can be used with any GR waveform approximant, with arbitrary parameterized deformations, to serve as model waveforms. In order to illustrate the workings of the method, we perform a range of numerical experiments in which simulated gravitational waves modeled in the restricted post-Newtonian, stationary phase approximation are added to Gaussian and stationary noise that follows the expected Advanced LIGO/Virgo noise curves.
118633851
Long-baseline super-beam experiments in Europe within LAGUNA
We explore the physics reach of several possible configurations for a Super-Beam experiment in Europe, focusing on the possibilities of discovering θ13, CP violation in the leptonic sector and the ordering of neutrino mass eigenstates. We consider the three different detector technologies: Water Cerenkov, Liquid Argon and Liquid Scintillator, and seven possible sites in Europe which would be able to host such a detector underground. The distances to these sites from CERN, where the beam would be originated, go from 130 km to 2300 km. The neutrino flux is optimized in each case as to match the first oscillation peak for each of the baselines under consideration. We also study the impact of several experimental factors in the performance of each detector technology.
53526002
Improvement of the low energy neutrino factory
The low energy neutrino factory has been proposed as a very sensitive setup for future searches for CP violation and matter effects. Here we study how its performance is affected when the experimental specifications of the setup are varied. Most notably, we have considered the addition of the ‘platinum’ �µ ! �e channel. We find that, whilst theoretically the extra channel provides very useful complementary information and helps to lift degeneracies, its practical usefulness is lost when considering realistic background levels. Conversely, an increase in statistics in the ‘golden’ �e ! �µ channel and, to some extent, an improvement in the energy resolution, lead to an important increase in the performance of the facility, given the rich energy dependence of the ‘golden’ channel at these energies. We show that a low energy neutrino factory with a baseline of 1300 km, muon energy of 4.5 GeV, and either a 20 kton totally active scintillating detector or 100 kton liquid argon detector, can have outstanding sensitivity to the neutrino oscillation parameters �13, � and the mass hierarchy. For our estimated exposure of 2.8×10 23 kton × decays per muon polarity, the low energy