Great response! Two questions: 1) Rather than a stable 'shield', what if there was one travelling very fast towards the star along a trajectory such that Urth would be in the wake? (Add velocity to mass to better deflect energy?) 2) Is the explosion spherically symmetrical? Can the planet be put into an alternative orbit to avoid the worst of it in combination with other protective measures?

Given the scale of energy release by a supernova, even using a neutron star as a shield might not be enough (outside of the obvious problems of using such a thing in the first place). So far as I know, the explosion will be spherically symmetrical, or at least close enough to make no real difference in the outcome. Pack your bags and move the planet; its the only way to be sure.

Not even a Neutron Star traveling very fast? If we can warp the planet out, can we warp in energy heading in an opposite direct from another exploding star?

The Supernova is outshining 100,000,000 stars. This is a truly incomprehensible amount of energy, and I would guess the Neutron star would be simply consumed by the outpouring of radiant energy.

I wonder if there isn't some possibility of using black holes as dynamic shielding (not necessarily terribly plausible, but assuming that an appropriately advanced übertech is permitted within physics). Of course, this would then beg the question of tidal forces.

Way beyond my pay grade. maybe make this a question and see who can answer this to you.

Well, good information so far. But in fact, the aliens really want to get the star detonated, not prevent its explosion. Also, "not being there" do not gets their message decrypted.

I was going to write an answer, but it was rather incomplete. Your talk of metamaterials actually fits in with what I was going to add: you may be able to cause the supernova to resonate through a very careful process over many many many years, such that when it does go supernova, there's some tweaked frequency spectra which permit your metamaterial solution to work.

@Thucydides Question edited. Hopefully it is clear enough now. If you think that there are still something unclear, tell me. About being nearby a supernova, read that answer: security.stackexchange.com/a/25392/17080

@Thucydides: and even if the neutron star is tough enough (and has enough gravitational pull) to remain intact, it'd still experience radiation pressure followed by pressure from the matter shockwave. So absolite best case, and like you I expect it's much worse than this, you take a neutron star to the face at something of the order of 8 miles per second...

Sol3a has an angular diameter of 8.376e-5 rad as seen from Sol, and thus subtends a solid angle of 2pi(1-cos(AD)) = 2.2e-8 steradians out of the sky's 4pi steradians. A supernova emits 1 foe (1e44 Joules) of energy; We must just block the ~1.75e35 Joules directed at our area of the sky. As it were, two Jupiters, colliding plastically at 14km/s and angle of 120 degrees at the right location between us and Sol, would have just that amount of kinetic energy going towards Sol. The radiation pressure would be just enough to bring the shield to a standstill (and to a boil). Adjust speed as needed.

@CharlesRockafellor The black hole would work in absorbing all incoming radiation and matter, but the problem is that it would also be pushed kinetically by the supernova blast wave. It would need an equal and opposite push to not be pushed towards the planet, which it would presumably then engulf as well.

@MarchHo There's another problem with black holes - gravitational lensing. The black hole will eat all the energy directed at it and then some, but it will also lens space-time such that a ring of the supernova's energy that wasn't directed at the planet will now be focused directly on the planet. The bending of light rays caused by the immense gravity of the black hole can thus make matters worse, not better.

@CharlesRockafellor A black hole big enough to shield the planet would be big enough to drop into the star and consume it before it has a chance to go supernova. At the end of the day the planet ends up orbiting a black hole.

If the technology were available to position a dynamic set of black holes, then it might be capable of opposing the kinetic push (and needn't be dropped into the star, hence could possibly be removed later), but there would still be the issue of lensing (which hadn't occurred to me, and for which I haven't thought of a workaround). GNACHOs might provide assistance vs. the lensing, but this is only a guess on my part.

@Thucydides The main problem with a neutron star shield is its size. Typically a neutron star has a diameter of 21 miles. The other trivial problems moving stellar mass objects, trying not to be fatally attracted by its gravity, and being subject to an x-rat flux. Besides if you have the capacity to move neutron stars. Surely simpler & more tractable shielding matter could be installed.

@IwillnotexistIdonotexist Interesting idea about the two colliding Jupiters, very different than everybody else's ideas. However, I think that it is still unlikely to work because debris of the two colliding and vaporizing Jupiters would obliterate the planet. Anyway, maybe you can elaborate it more, combining it with something else and fix whatever problems shows up. So, I invite you to post an answer. :D

@CharlesRockafellor It's the gravity of the situation. Any black hole big enough to shield a planet will be hugely more massive than the star itself, let alone the planet you're trying to protect. Both star and planet will plunge into the black hole along with the rest of their planetary system. en.wikipedia.org/wiki/Black_hole suggests 10^3 solar masses for an approx. Earth radius BH. Sorry! The cure is worst than the disease.

@CharlesRockafellor And in addition to all the great reasons why a black hole wouldn't work, let me add that it's quite possible that some of the matter that would be caught by the black hole would end up in orbit around it, while emitting huge amounts of lethal radiation. So even if you kept it in place so that it doesn't go straight through the planet, and so well focused that the lensing effect would make the radiation and matter go around the planet, you'd still fry the planet. Not a bad suggestion, but probably not good enough by far.

I'd imagine that the electric pulse from the supernova would exceed the strength of the fields holding molecules together - so choice of shield/refractor "material" will have negligible effect,

Unfortunately, these are all good reasons against a dynamic set of black holes (as well, there would be a need for continual fine-tuning of their orbits, in much the fashion that a Klemperer Rosette would require). Something tells me that similar issues would arise with GNACHOs.

@CharlesRockafellor Nope. A blackhole is a terrible idea. Funny thing. Blackholes are one of the brightest things in the universe. A blackhole is very efficient at converting matter into energy (50% efficient in fact). The supernova remnant being sucked into the blackhole would produce a secondary explosion that would be difficult to block, with the added bonus of adding a massive gravitational wave to the mix as well...