Is there any limit to how much sorcery a Pariah can cancel?

Question

In Warhammer 40k, Pariahs can cancel out the power of the Warp. Their power to do so is so great that Magnus the Red, one of the most powerful sorcerers and a Demon Prince, was unable to affect several Sisters of Silence when battling on Luna. Certainly demons also fear Nulls and Pariahs for a similar reason.

What are the limits of this power? Could a Pariah cancel the power of the Emperor of Mankind? The Chaos Gods?

Answer 1

I'm a bit late here, but the fluff has also advanced since this question was asked. Spoilers ahead concerning a certain psychic Inquisitor who lives in a chair.

In the Ravenor series, Inquisitor Ravenor finds the drug-addicted Zael Effernetti while investigating said drugs. Though he initially uses the child to find a local dealer, Ravenor keeps him around due to his terrifying latent psychic potential. Ravenor identifies Zael as being a mirror - a psychic that can reflect the psychic energies of those around him, or something like that. Ravenor himself is a very powerful psychic, but even so is unsettled by Zael's sheer potential.

Because of reasons (don't want to spoil too much), Zael entered a deep coma. Ravenor thought he was dangerous (more reasons), so he had Wystan Frauka, a pariah that worked with Ravenor, tend to the comatose child, effectively nullifying Zael's psychic abilities.

Except, it didn't.

In spite of being literally inches away from a pariah, Zael was such a powerful psychic that he was able to psychically communicate with Wystan! What's more, Zael's psychic presence was apparently so powerful that he permanently burned out Wystan's Null abilities! What's more, the effect seems to have been permanent, with no indication otherwise.

It should be noted that Wystan had successfully blocked multiple alpha level psychics, including Ravenor, on several occasions before this. There is no question whether Wystan's abilities were effective.

As for Zael... he was given to the Grey Knights and eventually became the Grey Knight Hyperion, the guy who broke Angron's sword.

Since this is a Black Library source, it canonically establishes that a Blank can be affected by psychic shenanigans if the psychic is strong enough. Just, the sheer power needed for this appears to be enough to put even an alpha level psychic to shame. More than that, it canonically establishes that a Blank's abilities can be permanently extinguished by a strong enough psychic.

In any case, I suspect this also answers the question of how Magnus and THE EM'PRAH were able to operate with the Sisters of Silence around.

TLDR: Black Library source with a psychic speaking psychically to a Blank and then burning out his Blankness.

Answer 2

EDIT

TLDR

• It seems they were more damaging to all psykers (even friendly) in previous versions
• It would seem that the assassins have more abilities than the sisters. Everything does explain that the pariah abilities can be more developed and stronger. This could be an identification at a limit to abilities.
• It would seem that units with the pariah ability were never able to be targeted due to their abilities. This tips the scale more in the unlimited arena.
• Having a bunch of them in the same place either stacks their abilities, extends the range, or some combination of the two. Though I might be more inclined to say that it is possible for the choir of the Astronomicon to drown out the pariahs and this would also put a limit on their abilities.
• Now I don't know for sure!

So I got a hold of my Codex Assassins (3rd Edition) and while I am sure GW has made updates to the order since here is a relatively quick review of what I found. I will also add after what is relevant from the new Index: Imperium 2 section...

Codex Assassins (3rd Edition)

• Page 20: When the Imperium first began to gather pariahs the High Lords found that all of them gathered in one place (their experimentation cells) the began blocking out the Astronomicon. This is when they began to understand the full extent of their power (However at the same time this also does demonstrate that at the very least more in one place extend the reach of their powers, if not simply stack their abilities to become more absolute... though the description does not really identify one way or the other)
• Page 22: Soulless Rule states that even non-psykers are affected and take penalties when doing something near a Culexus assassin
• Page 23: Psychic Abomination rule says 1. Tyranid Hive Tyrants can be permanently severed from the hive. 2.All psykers must pass Terror tests just because they start the turn within 8"
• Page 24: Warp Disturbance Rule says all psykers (even friendly) must roll each time they try to use a power if they are within 24" and in addition to failing the attack they can take a wound if they fail.
• Page 24: Life Drain Rule says that they can drain characteristics (WS, BS, S, T, LD) after rolling and the lost points are both lost for the remainder of the battle and can lead to death.
• Page 24: Daemons section (might have a mis-type in the beginning?) Says first that the assassin special attack does not affect daemons that are psykers; but then it says 1. this includes (daemon types) because they do no have psychic abilities 2. special attacks by the assassin count as psychic attacks and daemons receive no saving throw based on their daemonic aura
• Page 24: The assassination of the master of the adeptus astra telepathica section says that while connected to a life support system the master of the astra telepathica had his powers fully negated for life by an assassin that "blinded" his sight... the effect lingered after he was released.

Index: Imperium 2 (Pages 112 and 115)

• Abomination ability: can not be targeted by psyker powers and enemy psykers must subtract based on tests
• Life drain: only keeps models from making armour saves
• Etherium: all units WS and BS skills suffer when attacking this unit
• also mentions that the Culexus assassin saps away a psyker's very life force

TLDR

• Warp presence cancellation is total.
• There is no limit.
• All powers of the warp are cancelled.
• Physical manifestations can still exist around them.
• They are not the "final solution" to the problems of the warp.

So blanks/pariahs/nulls/etc. are all the same thing. They have no presence in the warp and furthermore repel the warp in its entirety. Everyone feels uneasy around them, even normal people with limited existence in the warp. Should an individual that has a significant presence in the warp come close enough to one of these individuals they will feel pain, headaches, etc. and find their abilities fully suppressed. This applies to ALL - Magnus, the Emperor, daemons, the Chaos Gods, etc.

Even in 8th Edition Sisters of Silence have the psychic abomination trait. This says

Psychic Abomination - This unit can never be targeted or affected by psychic powers in any way. In addition, enemy Psykers must subtract 1 from any psychic tests and Deny the Witch tests they take fro each unit with this ability that is within 18" of them (to a maximum of -4). Note however, that this ability has no effect whilst the unit is embarked upon a transport.

This is one of the reasons that Leman Russ was pretty much always found to have a band of Sisters of Silence in tow wherever he went. Though he himself had a presence in the warp (I believe the first instance of this was revealed in the novel A Thousand Sons by McNeill) he mainly kept his abilities suppressed and let his physical abilities speak for themselves.

While those with a significant warp presence (Magnus, the Emperor, etc) would all find their abilities suppressed it does not "take them out of the fight" completely. It merely means that they have to kill with some other means while they are near.

In addition, physical manifestations created through powers of the warp are unaffected by blanks. After they have been created or summoned anything (not including projections and such) with a tie to the warp will still exist. Once a daemon has been summoned it exists in a dimension separate from the warp and technically it has no tie to the warp anymore. It can still kill you even if you are near or are a blank.

However, I can not remember where I read it but I believe that a daemon or warp entity that is killed in the presence of a blank can not return to the warp and is therefore truly destroyed. Typically they are simply banished from "our" dimension and return to the warp where they can be summoned once again. (I have no source for this currently; I will see if I can find it...)

Despite their abilities blanks are not the solution to the problems of the warp. Since all someone would have to do is summon a fireball in the sky above them or a daemon in the "next room" and kill a blank in an "indirect" manner without taking warp abilities close to them.

Answer 3

I'd highly doubt they could do this. You must remember the Emperor himself commanded the Sisters of Silence and fought with them, so he must have been able to withstand their presence. Maybe he's just powerful enough that he can control it through sheer force of will. And I would imagine other such powerful beings such as the chaos Gods to be the same

Page 60 of Heralds of the siege confirms this. 2 sisters of silence are with Malcador but appear uncomfortable and trying to keep their distance due to his psychic might.

To add another piece of evidence to this, in the novel “the buried dagger” there is a mountain full of Pariahs (sisters of silence). Tylos Rubio is affected by them, but the novel states that malcador appears uneffected. As Malcador says he will descend further into the mountain, Garro states “you will be vulnerable. Robbed of every gift you have” to Malcador who replies “you think so? I am almost insulted”