SIMBAD references

The bulk Lorentz factor of the gamma-ray burst (GRB) ejecta (Γ₀) is a key parameter to understanding GRB physics. Liang et al. have discovered a correlation between Γ₀ and isotropic γ-ray energy: Γ₀∝E ^0.25_γ, iso, 52_. By including more GRBs with updated data and more methods to derive Γ₀, we confirm this correlation and obtain Γ₀ ≃ 91E ^0.29_γ, iso, 52_. Evaluating the mean isotropic γ-ray luminosities L_γ, iso_ of the GRBs in the same sample, we discover an even tighter correlation Γ₀≃ 249L ^0.30_γ, iso, 52_. We propose an interpretation to this later correlation. Invoking a neutrino-cooled hyperaccretion disk around a stellar mass black hole as the central engine of GRBs, we derive jet luminosity powered by neutrino annihilation and baryon loading from a neutrino-driven wind. Applying beaming correction, we finally derive Γ₀∝L ^0.22_γ, iso_, which is consistent with the data. This suggests that the central engine of long GRBs is likely a stellar mass black hole surrounded by a hyper-accreting disk.