I believe it is intended to be twin linked Las-Cannons
Twin Linked weapons are two of the same weapon linked together. As such it can sometimes be called a Twin Linked Las-Cannon (one twin linked weapon), other times it will be called Twin Linked Las-cannons (two Las Cannons linked together).
It fires one shot that can be re-rolled, as per twin linked weapons.
Which is the most recent book (I suspect its the siege of Vraks). A quick wiki search will probably tell you the release date.
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Oh, exalted for quick access to that list. Slight possible glitch though, The Arvus Lighter in the
IA book is 60 points, yet the same thing in the
HH red books is 75 (I know because I have been looking at all the different imperial fliers today trying to work out which ones suit my
IG army best fluff wise). I assumed I would be paying 75 points for it, but based on that list I would be paying 60 points. Truth is, it doesn't bother me to much either way as it is more about the fluff, or though having regular units being able to
DS would be nice from time to time, especially in narrative or scenario games.