Is the Blood Fury Tattoo’s damage doubled on a critical hit? [duplicate]

The question is as the title says, is the 4d6 necrotic damage doubled if you critted the attack that you then use the item’s ability on. The item text in question is below.

When you hit a creature with a weapon attack, you can expend a charge to deal an extra 4d6 necrotic damage to the target, and you regain a number of hit points equal to the necrotic damage dealt.