How to create this variable in Latex?

How do I create this in Latex? I tried $r^e_{\_}$ or $r^e\_$ but none give the variable as shown in the added picture.

>Solution :

You can move the underscore up a bit with

\documentclass{article}

\begin{document}

$r^{e}_{\raisebox{0.21em}{\_}}$ 

\end{document}