Related papers: Deceleration of arbitrarily magnetized GRB ejecta:…
In models for gamma ray burst afterglows, it is normally assumed that the external shock strongly amplifies the magnetic field and that this field maintains a steady value throughout the shocked region. We discuss the effects of modifying…
We present a relativistic-MHD numerical study of axisymmetric, magnetically driven jets with parameters applicable to gamma-ray burst (GRB) flows. We also present analytic expressions for the asymptotic jet shape and other flow parameters…
In a recent paper (Dai & Lu 1999), we have proposed a simple model in which the steepening in the light curve of the R-band afterglow of the gamma-ray burst (GRB) 990123 is caused by the adiabatic shock which has evolved from an…
One of the most energetic gamma-ray bursts GRB 110731A, was observed from optical to GeV energy range by Fermi and Swift Observatories, and by the MOA and GROND optical telescopes. The multiwavelength observations over different epochs…
We propose to explain the recent observations of GRB early X-ray afterglows with SWIFT by the dissipation of energy in the reverse shock which crosses the ejecta as it is decelerated by the burst environment. We compute the evolution of the…
Direct multi-dimensional numerical simulation is the most reliable approach for calculating the fluid dynamics and observational signatures of relativistic jets in gamma-ray bursts (GRBs). We present a two-dimensional relativistic…
Achromatic breaks in afterglow light curves of gamma-ray bursts (GRBs) arise naturally if the product of the jet's Lorentz factor \gamma and opening angle \Theta_j satisfies (\gamma \Theta_j) >> 1 at the onset of the afterglow phase, i.e.,…
The early X-ray afterglow for a significant number of gamma-ray bursts detected by the Swift satellite is observed to have a phase of very slow flux decline with time ($F_\nu \propto t^{-\alpha}$ with $0.2 \lesssim \alpha \lesssim 0.8$) for…
The prompt emission of the long, smooth, and single-pulsed gamma-ray burst, GRB $\textit{141028A}$, is analyzed under the guise of an external shock model. First, we fit the $\gamma$-ray spectrum with a two-component photon model, namely…
Based on light curves from the Swift Burst Analyser, we investigate whether a `dip' feature commonly seen in the early-time hardness ratios of Swift-XRT data could arise from the juxtaposition of the decaying prompt emission and rising…
We perform three-dimensional (3D) general-relativistic magnetohydrodynamic simulations to model the jet break-out from the ejecta expected to be produced in a binary neutron-star merger. The structure of the relativistic outflow from the 3D…
The shock model has successfully explained the observed behaviors of afterglows from long gamma-ray bursts (GRBs). Here we use it to investigate the so-called early afterglows from short GRBs, which arises from blast waves that are not…
Blackbody-dominated (BBD) gamma-ray bursts (GRBs) are events characterized by long durations and the presence of a significant thermal component following the prompt emission, as well as by the absence of a typical afterglow. GRB 101225A is…
The connection between Gamma-Ray Bursts (GRBs) and their afterglows is currently not well understood. Afterglow models of synchrotron emission generated by external shocks in the GRB fireball model predict emission detectable in the…
We find self-similar solutions to describe the interaction of spherically symmetric ejecta expanding at relativistic speeds with an ambient medium having a power law density distribution. Using this solution, the time evolution of the…
The afterglow of a gamma-ray burst (GRB) is commonly thought to be due to continuous deceleration of a relativistically expanding fireball in the surrounding medium. Assuming that the expansion of the fireball is adiabatic and that the…
GRB 120308A, a long duration $\gamma-$ray burst detected by {\it Swift}, was distinguished by a highly-polarized early optical afterglow emission that strongly suggests an ordered magnetic field component in the emitting region. In this…
The central engine and jet composition of gamma-ray bursts (GRBs) remain mysterious. Here we suggest that observations on polarization evolution of early optical afterglows may shed light on these questions. We first study the dynamics of a…
The early optical afterglow of GRB 050820a recorded by the RAPTOR telescope shows both a contribution from the prompt emission and the initial rise of the afterglow. It is therefore well-suited for the study of the dynamical evolution of…
We revisit the physical origin of the achromatic peaks and breaks observed several thousand seconds after the burst in the multi-wavelength afterglows of XRF 080330 and GRB 080710. Using a numerical afterglow model that consistently…