Nope, ASTB has to be done through your recruiter. Initiative=show up. Don't expect to take it that day (although possible, so be prepared) but someone should at least take notice and get back to you. If not, perhaps another recruiter, presuming this is your first step.
FYI search function is your friend, if only for the sake of not taking extra beatings from the senior participants. ;-) Also, read through threads dealing with any questions you have. Most questions have been repeated at least once in the past month or two.
Best of Luck!