Gamma Ray Bursts Spectral--Energy correlations: recent results

Abstract: The correlations between the rest frame peak of the EF_E spectrum of GRBs Epeak and their isotropic energy (E_iso) or luminosity (L_iso) could have several implications for the understanding of the GRB prompt emission. These correlations are presently founded on the time-averaged spectral properties of a sample of 95 bursts, with measured redshifts, collected by different instruments in the last 13 years (pre-Fermi). One still open issue is wether these correlations have a physical origin or are due to instrumental selection effects. By studying 10 long and 14 short GRBs detected by Fermi we find that a strong time-resolved correlation between E_peak and the luminosity L_iso is present within individual GRBs and that it is consistent with the time-integrated correlation. This result is a direct proof of the existence in both short and long GRBs of a similar physical link between the hardness and the luminosity which is not due to instrumental selection effects. The origin of the E_peak-L_iso correlation should be searched in the radiation mechanism of the prompt emission.