Implement Rewrite Module to have ApplicationName with querystring

How can I rewrite the URL to have application name + querystring? For example I have a web application with the following querystring

mywebsite/default.aspx?UserName=xyz

How can I have URL with the folllowing

mywebsite?xyz

I have managed to implement RewriteModule using HttpApplication on Begin_request event and currently I can use this query

http://mywebsite/?xyz  

Is there a way开发者_StackOverflow中文版 to have the url without /?

try,

rewrite ^/default\.aspx\?UserName=(.*)$ /?$1 last;