2006/03/31 by Xiaohong Zhao, J. M. Bai
Physics and Astronomy · #Afterglow #Astrophysics #Classical mechanics #Computational physics #Energy (signal processing) #Gamma-ray burst #Gamma-ray bursts and supernovae #Jet (fluid) #Kinetic energy #Mechanics #Physics #Shock (circulatory) #astro-ph
paper · pdf · doi:10.1086/510449
published as Astrophys.J.653:L1-L4,2006 · 9pages, 2figures, ApJL, accepted, appearing in Vol 653 (2006, Dec. 10)
openalex publication_date 2006/11/22 · arxiv created 2006/11/27 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
The high efficiency of converting kinetic energy into gamma rays estimated with late-time afterglows in gamma-ray burst (GRB) phenomenon challenges the commonly accepted internal-shock model. However, the efficiency is still highly uncertain because it is sensitive to many effects. In this Letter we study the sideways expansion effect of jets on estimating the efficiency. We find that this effect is considerable, reducing the efficiency by a factor of ~0.5 for typical parameters, when the afterglow data ~10 hr after the GRB trigger are used to derive the kinetic energy. For a more dense circumburst medium, this effect is more significant. As samples, taking this effect into account, we specifically calculate the efficiency of two bursts whose parameters were well constrained. Almost the same results are derived. This suggests that the sideways expansion effect should be considered when the GRB efficiency is estimated with the late afterglow data.