Revisiting gamma-ray burst afterglows with time-dependent parameters

The relativistic external shock model of gamma-ray burst （GRB） afterglows has been estab- lished with five free parameters, i.e., the total kinetic energy E, the equipartition parameters for electrons ee and for the magnetic field eB, the number density of the environment n and the index of the power- law distribution of shocked electrons p. A lot of modified models have been constructed to consider the variety of GRB afterglows, such as： the wind medium environment by letting n change with radius, the energy injection model by letting kinetic energy change with time and so on. In this paper, by as- suming all four parameters （except p） change with time, we obtain a set of formulas for the dynamics and radiation, which can be used as a reference for modeling GRB afterglows. Some interesting results are obtained. For example, in some spectral segments, the radiated flux density does not depend on the number density or the profile of the environment. As an application, through modeling the afterglow of GRB 060607A, we find that it can be interpreted in the framework of the time dependent parameter model within a reasonable range.

Not enough evidence to support the correlation between gamma-ray bursts and foreground galaxy clusters in the Swift Era

The correlation between distant Gamma-Ray Bursts （GRBs） and foreground galaxy clusters is re-examined by using the well localized （with an accuracy down to a few arcsec） Swift/XRT GRBs. The galaxy clusters are compiled from both the X-ray selected ROSAT brightest cluster sample （BCS） and the BCS extension by requiring δ ≥ 0° and b ≥ 20°. The Swift/XRT GRBs fulfilling the above selection criteria are cross-correlated with the clusters. Both Nearest-Neighbor analysis and the angular two-point cross-correlation function show that there is not enough evidence supporting the correlation between the GRBs and foreground clusters. We suggest that the non-correlation is probably related to the GRB number-flux relation slope.

X-ray and optical plateaus following the main bursts in GRBs and SNe Ⅱ-P: a hint about similar late injection behaviors?

We analyze the emission plateaus in the X-ray afterglow light curves of gamma-ray bursts （GRBs） and those in the optical light curves of type Ⅱ plateau su- pernovae （SNe Ⅱ-P） in order to study whether they have similar late energy injection behaviors. We show that correlations of bolometric energies （or luminosities） between the prompt explosions and the plateaus for the two phenomena are similar. The energy emitted by SNe II-P are at the lower end of the range of possible energies for GRBs. The bolometric energies （or luminosities） in the prompt phase Eexpl （or Lexpl） and in the plateau phase E_plateau （or L_plateau） share relations of E_expl ∝E _0.73±0.14_plateau and L_expl ∝ L^-0.70_plateau. These results may indicate a similar late energy injection behavior that produces the observed plateaus in these two phenomena.

Timescale Analysis of Spectral Lags

A technique for timescale analysis of spectral lags performed directly in the time domain is developed. Simulation studies are made to compare the time domain technique with the Fourier frequency analysis for spectral time lags. The time domain technique is applied to studying rapid variabilities of X-ray binaries and γ-ray bursts. The results indicate that in comparison with the Fourier analysis the timescale analysis technique is more powerful for the study of spectral lags in rapid variabilities on short time scales and short duration flaring phenomena.