Tachyonic (phantom) power-law cosmology

Tachyonic scalar field-driven late universe with dust matter content is considered. The cosmic expansion is modeled with power-law and phantom power-law expansion at late time, i.e. $z\lesssim 0.45$. WMAP7 and its combined data are used to constraint the model. The forms of potential and the field solution are different for quintessence and tachyonic cases. Power-law cosmology model (driven by either quintessence or tachyonic field) predicts unmatched equation of state parameter to the observational value, hence the power-law model is excluded for both quintessence and tachyonic field. In the opposite, the phantom power-law model predicts agreeing valued of equation of state parameter with the observational data for both quintessence and tachyonic cases, i.e. $w_{\phi, 0} = -1.49^{+11.64}{-4.08}$(WMAP7+BAO+$H_0$)and$ w{\phi, 0} = -1.51^{+3.89}_{-6.72} $(WMAP7)\mathrm{.}Thephantom-powerlawexponent$\beta$ must be less than about -6, so that the $-2<w_{\varphi ,0}<-1$. The phantom power-law tachyonic potential is reconstructed. We found that dimensionless potential slope variable $\mathrm{\Gamma }$ at present is about 1.5. The tachyonic potential reduced to $V=V_0{\varphi }^{-2}$ in the limit ${\mathrm{\Omega }}_{\mathrm{m},0}\to 0$.