The Æonic Orb is the rarest of the Necron weapon constructs.
Even during the war against the Ancients only a handful of these were used. Utilising the technological might of the living metal called Necrodermis, this weapon is fueled by a fragment of a star. It is rumored that the C'tan need to destroy an entire star in order to acquire the necessary components for the weapon's energy source. This essence is then encased in an orb-shaped containment field that sits on top of a skimmer platform, giving this weapon system frightening mobility, which is most often used to give the Æonic Orb the most favorable firing positions to take out enemy titans.
The firing mechanism of the weapon is as simple as it is effective. Merely by changing the containment field the Orb is capable of unleashing devastating bolts of energy that can cut virtually any material uncontested. Fortunately, after a shot of this solar flare weapon the Orb seems to require a significant amount of time to recharge. The Orb's secondary weapon, the solar burst, is simply a short-ranged, less-powerful version of the solar flare beam. This is compensated for by the beam affecting a larger area due to the increased radiation effects and the greater accuracy.
Upon destruction the Æonic Orb's containment field suffers a catastrophic failure, uncontrollably releasing the massive power held within. This results in a massive explosion, capable of levelling whatever army is foolish enough to be close to it. This destructive process both deals retribution to enemy forces that manage to bring down this weapon construct, and secure it from falling into the hands of the lesser races.
1: Games Workshop Website - Specialist Games pg 9 (Archived 2006)