The Early Afterglow Observation And A L_iso-E_p,z-Γ₀ Correlation In Gamma-Ray Bursts

The progress of gamma-ray bursts in Swift and Fermi era is reviewed and a series of work based on observation data are carefully presented. We select a sample of 34 gamma-ray bursts (GRBs) whose Γ0 values are derived with the onset peaks observed in the afterglow light curves (except for GRB 060218, whose Γ0 is estimated with its radio data), and found correlations among Γ0,the isotropic peak luminosity (Liso), and the peak energy (Ep,z) in the cosmological rest frame. The case GRB 060218, although deviated the L’iso-E’p relation of typical GRBs in the jet co-moving frame with 3σ, it still satisfies the multiple correlation in the jet co-moving frame. We argue that the Liso-Ep,z-Γ0 correlation may be more physical than the Liso - Ep,z correlation and explore the possible origins of this correlation and discuss its physical implications for understanding GRB jet composition and radiation mechanism. We also intend to reveal the evolution of central engine over long period by investigating the Γ0 variation of GRB 090618 and GRB 140508. We found that the Γ0 of first pulse is ～91 and the values of the following three pulses maintain around ～215, indicating the fireball is still accelerating during the photosphere emission.We investigate the properties of the prompt gamma-rays and the ambient medium using optical observations of GRB 111228A from 95 sec to about 50 hours after the burst trigger and the data observed with Swift and Fermi missions. Our joint optical and X-ray spectral fits to the afterglow data show that the ambient medium features as low dust-to-gas ratio. Incorporating the energy injection effect, our best fit to the afterglow light curves with the standard afterglow model via the Markov Chain Monte Carlo (MCMC) technique prefers a low medium density, which implies that the afterglow jet may be in a halo or in a hot ISM. It is found that GRB 111228A satisfies the Liso-Ep,z-Γ0 relation.