The Ep,i-Eiso correlation in gamma-ray bursts:: updated observational status, re-analysis and main implications

The correlation between the cosmological rest-frame nu F-nu spectrum peak energy, E-p,E-i, and the isotropic-equivalent radiated energy, E-iso, discovered by Amati et al.in 2002 and confirmed/extended by subsequent osbervations, is one of the most intriguing and debated observational evidences in gamma-ray burst (GRB) astrophysics. In this paper, I provide an update and a re-analysis of the E-p,E-i-E-iso correlation basing on an updated sample consisting of 41 long GRBs/X-ray flashes (XRFs) with firm estimates of z and observed peak energy, E-p,E-obs, 12 GRBs with uncertain values of z and/or E-p,E-obs, two short GRBs with firm estimates of z and E-p,E-obs and the peculiar subenergetic events GRB 980425/SN1998bw and GRB 031203/SN2003lw. In addition to standard correlation analysis and power-law fitting, the data analysis here reported includes modelling that accounts for sample variance. All 53 classical long GRBs and XRFs, including 11 Swift events with published spectral parameters and fluences, have E-p,E-i and E-iso values, or upper/lower limits, consistent with the correlation, which shows a chance probability as low as similar to 7 x 10(-15), a slope of similar to 0.57 (similar to 0.5 when fitting by accounting for sample variance) and an extra-Poissonian logarithmic dispersion of similar to 0.15, it extends over similar to 5 orders of magnitude in E-iso and similar to 3 orders of magnitude in E-p,E-i and holds from the closer to the higher z GRBs. Subenergetic GRBs (980425 and possibly 031203) and short GRBs are found to be inconsistent with the E-p,E-i-E-iso correlation, showing that it can be a powerful tool for discriminating different classes of GRBs and understanding their nature and differences. I also discuss the main implications of the updated E-p,E-i-E-iso correlation for the models of the physics and geometry of GRB emission, its use as a pseudo-redshift estimator and the tests of possible selection effects with GRBs of unknown redshift.