Question about Dedicated Powers on Intelligent Items

[Windrammer]

http://www.d20srd.org/srd/magicItems/intelligentItems.htm#intelligentItemGreaterPowers

Say I put the power to cast lightning bolt on a weapon, for the special purpose of slaying arcane spellcasters.

What happens when I run into a wizard, and what's the limit on the power? Does it keep shooting lightning off every round? Does it fire once? Is it completely up to the DM how much it makes use of this power?

[XionUnborn01]

I believe it's basically at-will, though the item can choose not to use it. I don't have a RAW citation or anything, it just seems to read that way.