\documentclass[12pt]{article}

\usepackage{pstricks} % To use the standard "xcolor" package with PSTricks
\usepackage{pst-node}
\usepackage{pst-plot}

\pagestyle{empty}

\begin{document}
\psset{unit=5mm,linewidth=.1}

\begin{center}
\begin{figure}
\begin{pspicture}(-8,-8)(8,8) % -.3 due to the coordinates under Ox
\SpecialCoor

\psaxes[arrows=<->,labels=none,ticks=none](0,0)(-8,-8)(8,8)
%\rput(8,-1){\psframebox[linecolor=white]{$t_1$}}
%\rput(1,8){\psframebox[linecolor=white]{$t_2$}}

\pscircle[linecolor=green,linestyle=dotted](0,0){2}
%\pscircle[linecolor=green,linestyle=dotted](0,0){4}

%\rput{30}{\psellipse[linecolor=red,linestyle=solid,rot=-90](0,0)(4,7)}
\rput{30}{\psellipse[linecolor=red,linestyle=solid,rot=-90](0,0)(2,7)}
 %ellipse, rotated by 30 degrees

%\psline[arrows=->,linecolor=blue](0,0)(-4,5.5)
\psline[arrows=->,linecolor=blue](0,0)(-3,5.5)
\rput(-4.5,6.5){\psframebox[linecolor=white]{\textcolor{blue}{$x$}}}

\rput(-6,4){\psframebox[linecolor=white]{\textcolor{red}{$C$}}}

%\rput(5,5){\psframebox[linecolor=white]{$_{x}t$}}
\rput(5,5){\psframebox[linecolor=white]{$y$}}

\end{pspicture}
\end{figure}
\end{center}

\end{document}