protesting 8(a) sole source award

8(a) has heard informally that another 8(a) has been awarded a sole source contract for work the 8(a) would have liked to bid.

8(a) does not know the size of the award, or even know positively the award has been made.

8(a) believes the contract could not have been awarded for less than $3.5 M unless it had been split into unreasonably small units.

8(a) wants to protest, either:

Contract was over $3.5 and should have been competed

Contract was under $3.5M because it was spit up, bad faith on part of government, etc etc

Regardless of the likelihood of success of such protests, what event triggers the 10 day period to go to GAO or the agency since the agency is not required to announce the award?