The (fairly) recent Black Library novel Atlas Infernal features an 'artifact' that is really the preserved fetus of an extra-super-high-level Untouchable; it's psychic nullification is so powerful that any psyker in its presence- up to and including Grey Knights- instantly keels over dead.
Of course, it's not a very good book, and that tends to be one of the things I take into account about interpreting 'official' canon...