Yong-Feng Huang

A comprehensive comparison of cosmological models from the latest observational data

We carry out a detailed investigation of some popular cosmological models in light of the latest observational data, including the Union2.1 supernovae compilation, the baryon acoustic oscillation measurements from the WiggleZ Dark Energy Survey and the cosmic microwave background information from the Wilkinson Microwave Anisotropy Probe seven-year observations, along with the observational Hubble parameter data. Based on the selection statistics of the models, such as the Akaike and the Bayesian information criteria, we compare different models to assess their worth. We do not assume a flat universe in the fitting. Our results show that the concordance ? cold dark matter (CDM) model remains the best model to explain the data, while the DvaliGabadadzePorrati model is clearly not favoured by the data. Among these models, the models whose parameters can reduce themselves to the ?CDM model provide good fits to the data. These results indicate that for the current data, there is no obvious evidence to support the use of any more complex models over the simplest ?CDM model.

Anti-glitch Induced by Collision of a Solid Body with the Magnetar 1E 2259+586

Glitches have been frequently observed in neutron stars. Previously these glitches unexceptionally manifest as sudden spin-ups that can be explained as due to impulsive transfer of angular momentum from the interior superfluid component to the outer solid crust. Alternatively, such spin-up glitches may also be due to large-scale crust-cracking events. However, an unprecedented anti-glitch was recently reported for the magnetar 1E 2259+586. In this case, the magnetar clearly exhibited a sudden spin-down, strongly challenging previous glitch theories. Here we show that the anti-glitch can be well explained by the collision of a small solid body with the magnetar. The intruder has a mass of about

CORRELATION BETWEEN PEAK ENERGY AND PEAK LUMINOSITY IN SHORT GAMMA-RAY BURSTS

1.1 \times 10^{21}

ON THE CORRELATION OF LOW-ENERGY SPECTRAL INDICES AND REDSHIFTS OF GAMMA-RAY BURSTS

g. Its orbital angular momentum is assumed to be antiparallel to that of the spinning magnetar, so that the sudden spin-down can be naturally accounted for. The observed hard X-ray burst and decaying softer X-ray emission associated with the anti-glitch can also be reasonably explained. Our study indicates that a completely different type of glitches as due to collisions between small bodies and neutron stars should exist and may have already been observed previously. It also hints a new way for studying the capture events by neutron stars: through accurate timing observations of pulsars.

Intensity distribution function and statistical properties of fast radio bursts

A correlation between the peak luminosity and the peak energy has been found by Yonetoku et al. as L{sub p} {proportional_to}E{sup 2.0}{sub p,i} for 11 pre-Swift long gamma-ray bursts (GRBs). In this study, for a greatly expanded sample of 148 long GRBs in the Swift era, we find that the correlation still exists, but most likely with a slightly different power-law index, i.e., L{sub p} {proportional_to} E{sup 1.7}{sub p,i}. In addition, we have collected 17 short GRBs with necessary data. We find that the correlation of L{sub p} {proportional_to} E{sup 1.7}{sub p,i} also exists for this sample of short events. It is argued that the radiation mechanism of both long and short GRBs should be similar, i.e., of quasi-thermal origin caused by the photosphere, with the dissipation occurring very near the central engine. Some key parameters of the process are constrained. Our results suggest that the radiation processes of both long and short bursts may be dominated by thermal emission, rather than by the single synchrotron radiation. This might put strong physical constraints on the theoretical models.

A CORRELATED STUDY OF OPTICAL AND X-RAY AFTERGLOWS OF GRBs

It was found by Amati et al. in 2002 that for a small sample of nine gamma-ray bursts (GRBs), more distant events appear to be systematically harder in the soft gamma-ray band. Here, we have collected a larger sample of 65 GRBs, whose time-integrated spectra are well established and can be well fitted with the so-called Band function. It is confirmed that a correlation between the redshifts (z) and the low-energy indices (α) of the Band function does exist, though it is a bit more scattered than the result of Amati et al. This correlation cannot be simply attributed to the effect of photon reddening. Furthermore, correlations between α and E peak (the peak energy in the νF ν spectrum in the rest frame), α and E iso (the isotropic energy release), and α and L iso (the isotropic luminosity) are also found, which indicate that these parameters are somehow connected. The results may provide useful constraints on the physics of GRBs.

Shallow Decay of X-ray Afterglows in Short GRBs: Energy Injection from a Millisecond Magnetar?

Fast Radio Bursts (FRBs) are intense radio flashes from the sky that are characterized by millisecond durations and Jansky-level flux densities. We carried out a statistical analysis on FRBs discovered. Their mean dispersion measure, after subtracting the contribution from the interstellar medium of our Galaxy, is found to be

Afterglow Light Curves of Jetted Gamma-ray Burst Ejecta in Stellar Winds

\sim 660\,\rm pc\,cm^{-3}

A Model of White Dwarf Pulsar AR Scorpii

, supporting their being from cosmological origin. Their energy released in radio band spans about two orders of magnitude, with a mean value of

The Origin of the Prompt Emission for Short GRB 170817A: Photosphere Emission or Synchrotron Emission?

\sim 10^{39}