Constraining a variable dark energy model from the redshift-luminosity
  distance relations of gamma-ray bursts and type Ia supernovae
  There are many kinds of models which describe the dynamics of dark energy
(DE). Among all we adopt an equation of state (EoS) which varies as a function
of time. We adopt Markov Chain Monte Carlo method to constrain the five
parameters of our models. As a consequence, we can show the characteristic
behavior of DE during the evolution of the universe. We constrain the EoS of DE
with use of the avairable data of gamma-ray bursts and type Ia supernovae (SNe
Ia) concerning the redshift-luminosity distance relations. As a result, we find
that DE is quintessence-like in the early time and phantom-like in the present
epoch or near the future, where the change occurs rather rapidly at $z\sim0.3$.
