2005/02/28 by David Eichler, Eli Waxman · 1 citation
Physics and Astronomy · #Astro and Planetary Science #Astrophysics and Cosmic Phenomena #Gamma-ray bursts and supernovae #astro-ph
paper · pdf · doi:10.1086/430596
published as Astrophys.J. 627 (2005) 861-867 · Accepted to ApJ; Improved and expanded discussion of observational signatures (sec. 3)
arxiv created 2005/03/24 · openalex publication_date 2005/07/06 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/31
Afterglow observations are commonly used to determine the parameters of GRB explosions, the energy E , surrounding density n , postshock magnetic field equipartition fraction B , and electron equipartition fraction e , under the frequently made assumption that the efficiency of electron "injection" into relativistic shock acceleration is high, i.e., that the fraction f of electrons that undergo acceleration is f ≈ 1. We show that the value of f cannot be determined by current observations, since currently testable model predictions for a parameter choice E ' = E / f , n ' = n / f , = f B , = f e are independent of the value of f for m e / m p ≤ f ≤ 1. Current observations imply that the efficiency f is similar for highly relativistic and subrelativistic shocks and plausibly suggest that f ~ 1, quite unlike the situation in the Crab Nebula. However, values m e / m p ≤ f ≪ 1 cannot be ruled out, implying a factor m e / m p uncertainty in determination of model parameters. We show that early, ≤10 hr, radio afterglow observations, which will be far more accessible in the Swift era, may provide constraints on f . Such observations will therefore provide a powerful diagnostic of GRB explosions and of the physics of particle acceleration in collisionless shocks.