Line
This weapon fires a projectile in a straight line that pierces through multiple creatures or obstacles. When attacking with such a weapon, make a single attack roll and compare it to the relevant Armor Class of all creatures and objects in a line extending to the weapon’s listed range increment. Roll damage only once. The weapon hits all targets with an AC equal to or lower than the attack roll. However, if an attack fails to damage a creature or obstacle hit in the line (typically due to damage reduction or hardness), the path is stopped and the attack doesn’t damage creatures farther away. A line weapon can’t damage targets beyond its listed range. If you score a critical hit, that effect applies only to the first target hit in the line, and you roll the critical damage separately. If multiple creatures are equally close, you choose which one takes the effects of the critical hit. A line weapon doesn’t benefit from feats or abilities that increase the damage of a single attack (such as the operative’s trick attack).
Source
Core Rulebook pg. 181