Not sure you can close a window that was opened from Flash, but if you can...
One not-so-well-advertised fact is that you *can* "find" a window on a page by its name, assuming that your code opened it.
So you could do:
Note that you don't pass a URL to the window.open. In this usage, *if* the window of that name already exists, you get a handle to it.
var radioWin = window.open("","radio");
if ( radioWin != null ) radioWin.close( );
Caution: If the window of that name does *NOT* exist, this code will open one (blank) very briefly until the close( ) then closes it.
NOT TESTED IN ALL BROWSERS! Works in MSIE and FF.
Note: YOU must be the "owner" of the popped up window, of course. That is, your code must be. That's why I worry about invoking this from Flash: Not sure whether the browser sees Flash as same "owner" or not. I'd be curious to know if it works.