121504005
HXMT: A Chinese High-Energy Astrophysics Mission
The Hard X-ray Modulation Telescope mission HXMT is mainly devoted to performing a hard X-ray all-sky imaging survey with both high sensitivity and high spatial resolution In the energy range of 20 - 250 keV HXMT can perform full-sky hard X-ray survey with angular resolution 5 prime position accuracy 1 prime and sensitivity better than Integral IBIS and Swift BAT HXMT can also make high signal-to-noise ratio pointing observations of scientific hot spot sources with sensitivity sim 3 0 times 10 -7 ph cm -2 s -1 keV -1 3 100keV 10 5 s for detailed temporal and spectral studies HXMT was selected in 2000 as a project under the Major State Basic Research Program of China for its feasibility and technical demonstration study and in October 2005 HXMT entered the full design phase and was listed as a candidate for the first dedicated astronomy satellite around 2010
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.
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.
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.
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.
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.
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.
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.
59497924
Towards a generic test of the strong field dynamics of general relativity using compact binary coalescence: Further investigations
In this paper we elaborate on earlier work by the same authors in which a novel Bayesian inference framework for testing the strong-field dynamics of General Relativity using coalescing compact binaries was proposed. Unlike methods that were used previously, our technique addresses the question whether one or more 'testing coefficients' (e.g. in the phase) parameterizing deviations from GR are non-zero, rather than all of them differing from zero at the same time. The framework is well-adapted to a scenario where most sources have low signal-to-noise ratio, and information from multiple sources as seen in multiple detectors can readily be combined. In our previous work, we conjectured that this framework can detect generic deviations from GR that can in principle not be accomodated by our model waveforms, on condition that the change in phase near frequencies where the detectors are the most sensitive is comparable to that induced by simple shifts in the lower-order phase coefficients of more than a few percent (~ 5 radians at 150 Hz). To further support this claim, we perform additional numerical experiments in Gaussian and stationary noise according to the expected Advanced LIGO/Virgo noise curves, and coherently injecting signals into the network whose phasing differs structurally from the predictions of GR, but with the magnitude of the deviation still being small. We find that even then, a violation of GR can be established with good confidence.
118554862
Exploring the Earth matter effect with atmospheric neutrinos in ice
We study the possibility to perform neutrino oscillation tomography and to determine the neutrino mass hierarchy in kilometer-scale ice Cerenkov detectors by means of the theta13-driven matter effects which occur during the propagation of atmospheric neutrinos deep through the Earth. We consider the ongoing IceCube/DeepCore neutrino observatory and future planned extensions, such as the PINGU detector, which has a lower energy threshold. Our simulations include the impact of marginalization over the neutrino oscillation parameters and a fully correlated systematic uncertainty on the total number of events. For the current best-fit value of the mixing angle theta13, the DeepCore detector, due to its relatively high-energy threshold, could only be sensitive to fluctuations on the normalization of the Earth's density of \Delta\rho \simeq \pm 10% at ~ 1.6 sigma CL after 10 years in the case of a true normal hierarchy. For the two PINGU configurations we consider, overall density fluctuations of \Delta\rho \simeq \pm 3% (\pm 2%) could be measured at the 2 sigma CL after 10 years, also in the case of a normal mass hierarchy. We also compare the prospects to determine the neutrino mass hierarchy in these three configurations and find that this could be achieved at the 5 sigma CL, for both hierarchies, after 5 years in DeepCore and about 1 year in PINGU. This clearly shows the importance of lowering the energy threshold below 10 GeV so that detectors are fully sensitive to the resonant matter effects.