How do I add the xsi and xmlns:xsi tags to an XML file using Linq in C#?

I've never quite understood this and am struggling again.  I need my XML file to look like this:

<?xml version="1.0"?>

-<eTest xsi:noNamespaceSchemaLocation="eTest-Schema.xsd" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
+<GLEntries>
</eTest>

I am using this technique:

                    XDocument ardoc = new XDocument();
                    XElement eTest= new XElement("eTest");
                    ardoc.Add(eTest);
                    ardoc.Save(this._ARExpPath + "AR" + dt.Date.ToString("yyyyMMdd") + ".XML");

I don't know how to get the xsi and xmlns:xsi tags (attributes?) into the eTest element.

Thanks.