We constrain holographic dark energy ( HDE ) with time varying gravitational coupling constant in the framework of the modified Friedmann equations using cosmological data from type Ia supernovae , baryon acoustic oscillations , cosmic microwave background radiation and X-ray gas mass fraction .
Applying a Markov Chain Monte Carlo ( MCMC ) simulation , we obtain the best fit values of the model and cosmological parameters within 1 \sigma confidence level ( CL ) in a flat universe as : \Omega _ { b } h ^ { 2 } = 0.0222 ^ { +0.0018 } _ { -0.0013 } , \Omega _ { c } h ^ { 2 } = 0.1121 ^ { +0.0110 } _ { -0.0079 } , \alpha _ { G } \equiv \dot { G } / ( HG ) = 0.1647 ^ { +0.3547 } _ { -0.2971 } and the HDE constant c = 0.9322 ^ { +0.4569 } _ { -0.5447 } .
Using the best fit values , the equation of state of the dark component at the present time w _ { d 0 } at 1 \sigma CL can cross the phantom boundary w = -1 .