Use of 真的 as adverb: are 我真要走了 and 我真的要走了 equally correct? I came across the sentence: "我真的要走了".

I am wondering why it has the 的. I didn't know 真 needed a 的 to be an adverb, or that it was even ok. 

Is it equally correct to say "我真要走了"? Or is "我真的要走了" better?
"我真要走了" and "我真的要走了" are both good expressions. They are in fact no different at all. "真" and "真的" are both adverbs here.