A TIGHT L_iso-E_p,z-Γ₀ CORRELATION of GAMMA-RAY BURSTS

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 investigate the correlations among Γ₀, the isotropic peak luminosity (L_iso), and the peak energy (E_p,z) of the νf_ν spectrum in the cosmological rest frame. An analysis of pair correlations among these observables well confirms the results reported by the previous papers. More interestingly, a tight correlation among L_iso, E_p,z, and Γ₀ is found from a multiple regression analysis, which takes the form of L_iso ∝ E_p,z^{1.34 ± 0.14} Γ₀^{1.32± 0.19} or E_p,z ∝ L_iso^{0.55 ± 0.06} Γ₀^{-0.50± 0.17} Nine other GRBs whose Γ₀ are derived via the pair production opacity constraint also follow such a correlation. Excluding GRB 060218, the L_iso-E_p,z-Γ₀ correlation is valid, and it even holds in the jet co-moving frame. However, GRB 060218 deviates the L_iso'-E_p' relation of typical GRBs in the jet co-moving frame with 3σ. We argue that the L_iso-E_p,z-Γ₀ correlation may be more physical than the L_iso-E_p,z correlation, since physically the relationship between the observed L_iso and E_p,z not only depends on radiation physics, but also depends on the bulk motion of the jet. We explore the possible origins of this correlation and discuss its physical implications for understanding GRB jet composition and radiation mechanisms.