Addressing the circularity problem in the Ep-Eiso correlation of gamma-ray bursts

We here propose a new model-independent technique to overcome the circularity problem affecting the use of gamma-ray bursts (GRBs) as distance indicators through the use of E-p-E-iso correlation. We calibrate the E-p-E-iso correlation and find the GRB distance moduli that can be used to constrain dark energy models. We use observational Hubble data to approximate the cosmic evolution through Bezier parametric curve obtained through the linear combination of Bernstein basis polynomials. In doing so, we build up a new data set consisting of 193 GRB distance moduli. We combine this sample with the supernova JLA data set to test the standard Lambda CDM model and its omega CDM extension. We place observational constraints on the cosmological parameters through Markov Chain Monte Carlo numerical technique. Moreover, we compare the theoretical scenarios by performing the Akaike and Deviance Information statistical criteria.the 2 sigma level, while for the omega CDM model we obtain Omega(m )= 0.34(-0.15)(+0.13) and omega = -0.86(-0.38)(+0.36 )at the 2 sigma level. Our analysis suggests that Lambda CDM model is statistically favoured over the omega CDM scenario. No evidence for extension of the Lambda CDM model is found.