Can you pass a police car who is in the right lane, under the speed limit, with its yellow lights flashing?

I came upon this situation a few days ago, and wasn't sure what to do, so I just followed behind. He was in the right lane, going around 5 mph under the limit. He had his yellow lights on top of the car flashing, the ones where each light comes on, left to right.. kind of like they were chasing each other. He drove like that for about a mile. He turned off the lights, resumed speed, drove for about 500 ft, then turned off the road onto another.

This was in Pennsylvania if that makes a difference.