Constraining cosmological parameters by Gamma Ray Burst X - ray
  afterglow lightcurves
  We present the Hubble diagram (HD) of 66 Gamma Ray Bursts (GRBs) derived
using only data from their X - ray afterglow lightcurve. To this end, we use
the recently updated L_X - T_a correlation between the break time T_a and the X
- ray luminosity L_X measured at T_a calibrated from a sample of Swift GRBs
with lightcurves well fitted by the Willingale et al. (2007) model. We then
investigate the use of this HD to constrain cosmological parameters when used
alone or in combination with other data showing that the use of GRBs leads to
constraints in agreement with previous results in literature. We finally argue
that a larger sample of high luminosity GRBs can provide a valuable information
in the search for the correct cosmological model.
