I was flying an Asp with 6/B shields, shield boosters and Military bulkheads (not much cargo space though). About two hours ago, while still two jumps away, I was interdicted and attacked by someone - I never did see who - my shields were gone before I could even turn towards him (it only took two or 3 hits - I had 2 pips to shields), so I fled - 4 pips to engines, retract weapons, max boost, max thrust, working my joystick and thrusters like mad while waiting to High Wake out of there (I'd submitted to the interdiction to cut the cool-down time). He hit me twice while my FSD charged and I jumped away with just 19% hull and a cracked windscreen.
I'm guessing he had Railguns...
With that kind of alpha damage, I'd have to agree with railguns or hammers. If he had plasma, there would be a miss or two there and you would have seen a shot go past you. I ran an FAS with 4 hammers not long ago. Incredibly fun and crazy damage output. I cooked myself while dealing it out, but it was pretty fun. Even heat sinks couldn't save me from frying. A setup like that could appear and sound like a single shot while you're being hit with 12 individual bolts.
I've since downsized to 2 hammers.