Constraining a New Type of Dark Energy Model from Present Observations

We propose a new type of dark energy (DE) model, in which the equation of state of DE ω de is a simple function of the fractional energy density de instead of the redshift z. We assume three DE models of this type, and fit them with present observations to get constraints of DE, which are also compared with the CPL model. It is shown that a suitable ω de (Ωde ) model can give smaller χ2 or smaller errors of ω de than that of the CPL model. This new type of DE model can help to study the essential properties and nature of DE.