2009MNRAS.393.1209F

For a sample of long γ-ray bursts (GRBs) with known redshift, we study the distribution of the evolutionary tracks on the rest-frame luminosity-peak energy L_iso- E'_pdiagram. We are interested in exploring the extension of the `Yonetoku' correlation to any phase of the prompt light curve, and in verifying how the high-signal prompt duration time, T'<sub>f</sub>, in the rest frame correlates with the residuals of such correlation. For our purpose, we separately analyse two samples of time-resolved spectra corresponding to 32 GRBs with peak fluxes F<sub>p</sub>> 1.8 phot/cm2/s from the Swift-BAT detector, and seven bright GRBs from the Compton Gamma-ray Observatory (CGRO)-BATSE detector previously processed by Kaneko et al. After constructing the L<sub>iso</sub>- E'<sub>p</sub>diagram, we discuss the relevance of selection effects, finding that they could significantly affect the correlation. However, we find that these effects are much less significant in the L<sub>iso</sub>T'<sub>f</sub>- E'<sub>p</sub>diagram, where the intrinsic scatter reduces significantly. We apply further corrections in order to reduce the intrinsic scatter even more. For the subsamples of GRBs (seven from Swift and five from CGRO) with measured jet break time, t<sub>j</sub>, we analyse the effects of correcting L<sub>iso</sub> by jet collimation. We find that (i) the scatter around the correlation is reduced, and (ii) this scatter is dominated by the internal scatter of the individual evolutionary tracks. These results suggest that the time-integrated `Amati' and `Ghirlanda' correlations are consequences of the time-resolved features, not of selection effects, and therefore call for a physical origin. We finally remark the relevance of looking inside the nature of the evolutionary tracks.