A Comprehensive Analysis of Text-Book-Version Afterglow Light curves of Gamma-Ray Bursts and Implication for Universal Radiation Physics of Baryonic Jets

The standard external shock model in the thin-shell scenario predicts an onset bump in the early optical afterglow light curves of gamma-ray bursts (GRBs). We collect such a textbook-version light curve sample of 30 GRBs, and derive the jet properties from our joint fit to their X-ray and optical afterglow light curves. It is found that the distributions of the isotropic initial Lorentz factors (₀), the deceleration radii (R ₃₄₂), and the magnetic field strength (B₀) are log-normal, but the distributions of the isotropic kinetic energy (E ₊, ₈ₒ₎), medium density (n₀), and the magnetization parameter (₁B/ₑ) are tentatively bimodal. A tight R ₃₄₂-B₀-₁ relation is found. It infers a universal ₑ E ₊, ₈ₒ₎ among bursts, plausibly supporting the previous argument of a universal GRB radiation energy among GRBs. A jet break is required for modeling the light curves of 26 GRBs. The distributions of the jet opening angles and the jet-corrected kinetic energies log-normally center at ₉, ₂/ rad=-1. 51 (standard deviation =0. 27) and (E ₊, ₉, ₂/ erg) =51. 78 (=0. 54), respectively. Those GRBs (19 GRBs), whose prompt gamma-ray emission is well estimated with broad energy-band observations, satisfy the previously discovered L, ₏, ₈ₒ₎-E ₏, ₙ-₀ relation, and their gamma-ray radiation efficiencies log-normally distribute in the range from 0. 04\% to 10\% with a central value of 0. 42\%. Such a low efficiency favors the baryonic fireball model, and the distribution of their baryon mass loading in the GRB ejecta log-normally centers at (M ₅₁, ₂/M ₒₔ₍) =-5 (=0. 75).