Rest frame light curves of Swift GRBs

— We have computed the luminosity rest frame light curves of the first 40 Gamma-ray bursts (GRBs) detected by Swift with well established redshift. We studied average properties of the light curves in the four subsamples of bursts given by z < 1, 1 < z < 2, 2 < z < ∼ 4, and z > ∼ 4. We conclude that all the last three subsamples share the same morphology and the same luminosity range. Very high redshift (z > ∼ 4) GRBs detected up to now are not intrinsically longer than lower redshift long GRBs. Nearby long GRBs (z < 1) are fainter than average. Possible selection effect are under investigation. We have computed the 0.2−10 keV luminosity rest frame light curves of the first 40 GRBs detected by Swift with well established redshift. The sample covers GRBs up to May 2006 and includes of 9 very high redshift (z > ∼ 4) GRBs and 3 short GRBs (GRB 050509B, GRB 050724 and GRB 051221A, all with redshift z < 1). More than half of the selected sources (26 over 40) show flares during the XRT observation. Our sample is definitely larger than samples used in previous works on Swift GRBs luminosity light curves (Chincarini et al. 2005, 7 GRBs used; Nousek et al. 2006, 14 GRBs used) and is comparable to the sample of GRBs with redshift triggered by the pre-Swift missions (e.g. BeppoSAX, HETE II, INTEGRAL) that consists of 46 objects. However, the redshift distributions of the two samples are substantially different (see Fig. 1): pre-swift bursts have an average redshift of 1.22 and a larger fraction of the population at low redshift, while Swift bursts have an average redshift of 2.44 and a flat distribution up to z = 5, with a single source at redshift z = 6.3 (GRB 050904; Cusumano et al. 2006). Several