According to the weapon description in the image, the arc battery of the Harrrower cruiser are supposed to be 180 degrees left & right.
That would mean 360 degrees cover around the ship.
However, when you view the firing arcs as displayed in the picture, by hovering over the weapon, it is only 90 degrees left & 90 rigtht, for a total of 180 degrees cover.
Necron Harrowerr cruiser display Lightning arc battery wrong