As far as Latin alphabet approximates, I'd say "aw" is pretty perfect. Because I think most accents will pronounce "thought" as if you add a t to "thaw". It's just that what that means in terms of the actual articulation varies a lot.

So, Americans with the cot-caught merger will pronounce it with the "cot" vowel, which is what I was trying to get across. UK/Aus/NZ don't all pronounce it the same as each other, but do for the most part pronounce it with the same vowel as they would use for the word "or". And "thaw", in our non-rhotic accents, is the same as Thor.

So "aw" works either way. Nice find!