From Destinypedia, the Destiny wiki
This weapon has two separate firing modes: a concentrated beam and a rapid barrage.
The beam firing mode requires the weapon to charge up before firing, but the beams fired travel across the area almost instantaneously, have pinpoint accuracy, deal very high impact damage, and create SIVA Swarms upon impact with any surface. These SIVA Swarms take up a large portion of the available area, deal rapid damage to Guardians inside of them, and obscures player vision. Aksis is capable of constantly laying down these swarms without pause, rendering many parts of the area unsafe.
The barrage firing mode releases a volley of explosive artillery projectiles in rapid succession. These projectiles travel in an arc, but have fast muzzle velocity, high impact damage, and a large blast radius. Because of the rate of fire, Aksis can strip a Guardian's shield quickly. Since this is the mode that is used the most, lots of time must be spent hiding behind cover.
- The SIVA Cannon seems to resemble a heavily modified Shrapnel Launcher with elements of the Sleeper Simulant in the design.