HN has moderators that track things like that and can see where the upvotes are coming from and determine if the attention is genuine. If you're concerned, the correct approach is to email them about it, not post vague accusations of astroturfing.
From the guidelines:
> Please don't post insinuations about astroturfing, shilling, brigading, foreign agents, and the like. It degrades discussion and is usually mistaken. If you're worried about abuse, email hn@ycombinator.com and we'll look at the data.
From the guidelines:
> Please don't post insinuations about astroturfing, shilling, brigading, foreign agents, and the like. It degrades discussion and is usually mistaken. If you're worried about abuse, email hn@ycombinator.com and we'll look at the data.