Narrow Results

A theoretical attempt to identify the physical process responsible for the afterglow emission of Gamma-Ray Bursts (GRBs) is presented, leading to the occurrence of thermal emission in the comoving frame of the shock wave which gives rise to the bursts. The determination of the luminosities and spectra involves integration over an infinite number of Planckian spectra, weighted by appropriate relativistic transformations, each one corresponding to a different viewing angle in the past light cone of the observer. The relativistic transformations have been computed using the equations of motion of GRBs within our theory, giving special attention to the determination of the equitemporal surfaces. The only free parameter of the present theory is the "effective emitting area" in the shock wave front. A self-consistent model for the observed hard-to-soft transition in GRBs is also presented. When applied to GRB 991216 a precise fit (χ²≃1.078) of the observed luminosity in the 2–10 keV band is obtained. Similarly, detailed estimates of the observed luminosity in the 50–300 keV and in the 10–50 keV bands are obtained.

The softening of the gamma ray burst (GRB) afterglow bears remarkable similarities to the frequency evolution in a sonic boom. At the front end of the sonic boom cone, the frequency is infinite, much like a GRB. Inside the cone, the frequency rapidly decreases to infrasonic ranges and the sound source appears at two places at the same time, mimicking the double-lobed radio sources. Although a "luminal" boom violates the Lorentz invariance and is therefore forbidden, it is tempting to work out the details and compare them with existing data. This temptation is further enhanced by the observed superluminality in the celestial objects associated with radio sources and some GRBs. In this article, we calculate the temporal and spatial variation of observed frequencies from a hypothetical luminal boom and show remarkable similarity between our calculations and current observations.

We revisit the vertical structure of neutrino-dominated accretion flows (NDAFs) in spherical coordinates with a new boundary condition based on the mechanical equilibrium. The solutions show that the NDAF is significantly thick. The electron fraction approaches 0.5 at the surface of the disk in the outer region, which means that the matter in these regions is almost composed of α-particles and electrons in non-degenerate phase. It may be an implication for the origin of heavy nuclei in GRBs.

The ultra-relativistic precessing jet in gamma-ray bursts (GRBs) may be responsible for the complex structure in GRBs' light curves. In this work, we study the gravitational radiations of jet precession induced by neutrino-dominated accretion disks around black holes. In our model, the jet and the inner part of the disk may precess along with the black hole, which is driven by the outer part of the disk. Gravitational radiations are therefore expected to be significant from this precession system. Based our numerical results, we find that it is possible for DECIGO and BBO to detect such gravitational radiations regardless of GRBs' black hole masses, particularly for GRBs in the Local Group.

By solving a set of coupled hydrodynamical and microphysical equations with some appropriate boundary conditions, we obtain three global solutions of typical neutrino-dominated accretion flows around different spinning black holes. Our results reveal that the effect of black hole spin on the flows is restricted within inner parts of neutrino-dominated regions.

Previous studies have found that the width of gamma-ray burst (GRB) pulse is energy dependent^1-2 and its origin keeps unknown. Here we find combining the curvature effect and the intrinsic Band spectrum could naturally result in the energy dependence of GRB pulse width. Our result suggests that the GRB decay phase is indeed related to the so-called curvature effect. A natural expectation of our study is for bursts with single power law, not Band spectrum, pulse width will not be energy dependent in our consideration.

We analyze GRB060607A within the fireshell model. The temporal properties of the flares observed in the decaying phase of the X-ray afterglow are reproduced by the same mechanism than the prompt emission light curve: the interaction of the optically thin fireshell with overdense CircumBurst Medium (CBM) clumps. The main observational differences between these two regimes depend on the typical dimensions of the clumps with respect to the visible area of the fireshell.

In the standard baryonic fireball model, the prompt MeV emission of the Gamma-ray bursts has been attributed to the synchrotron radiation of the electrons accelerated in the internal shocks. Such a model, if correct, requires a very high bulk Lorentz factor of the fast shells. The thermal radiation of these fast shells is too strong to be hidden by the non-thermal internal shock emission. The non-detection of such a thermal component in the spectrum of most GRBs in turn challenges the baryonic fireball model.