STUDY OF POSSIBLE SYSTEMATICS IN THEL*_X-T*_aCORRELATION OF GAMMA-RAY BURSTS

Gamma Ray Bursts (GRBs) are the most energetic sources in the universe and among the farthest known astrophysical sources. These features make them appealing candidates as standard candles for cosmological applications so that studying the physical mechanisms for the origin of the emission and correlations among their observable properties is an interesting task. We consider here the luminosity L*X - break time Ta* (hereafter LT) correlation and investigate whether there are systematics induced by selection effects or redshift dependent calibra- tion. We perform this analysis both for the full sample of 77 GRBs with known redshift and for the subsample of GRBs having canonical X-ray light curves, hereafter called U0095 sample. We do not find any systematic bias thus con- firming the existence of physical GRB subclasses revealed by tight correlations of their afterglow properties. Furthermore, we study the possibility of applying the LT correlation as a redshift estimator both for the full distribution and for the canonical lightcurves. The large uncertainties and the non negligible intrin- sic scatter make the results not so encouraging, but there are nevertheless some hints motivating a further analysis with an increased U0095 sample.