Fermi Gamma-ray Space Telescope

A Tight L_iso? Ep,z? ?_0 Correlation of Gamma-Ray Bursts

E. W. Liang
T. T. Lin, J. Lyu, R. J. Lu, J. Zhang, B. Zhang

Abstract:

We select a sample of 34 GRBs whose ?_0 values are derived with the onset peaks observed in the afterglow lightcurves (except for GRB 060218 whose ?_0 is estimated with its radio data), and investigate the correlations among ?_0, the isotropic peak luminosity (L_iso), and the peak energy (Ep,z) of the ?f? 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, Ep,z, and ?_0 is found from a multiple regression analysis, which takes the form of L_iso?Ep,z^(1.340.14)?_0^(1.320.19) or Ep,z?L_iso^(0.550.06)?_0^(?0.500.17). Nine other GRBs whose ?_0 are derived via the pair production opacity constraint also follow such a correlation. In the jet co-moving frame, the L_iso??E?p??_0 correlation also holds. An L?_iso?E?p relation is also found for typical GRBs, but the low-?_0 GRB 060218 deviates from this relation at a 3? confidence level. We argue that the L_iso? Ep,z? ?_0 correlation may be more physical than the L_iso?Ep,z correlation, since physically the relationship between the observed L_iso and Ep,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 mechanism.