It has to produce radiation patterned so as to imitate interstellar parallax. And it has to physically emit very high energy particles such as we detect on earth in cosmic rays.

It doesn't have to be "perfect". Keep in mind the old joke about the experimental and theoretical physicist:

Experimental physicist: I did an experiment and the sign on constant X came out positive.

Theoretical physicist: It's easy to see that it should be that way because of reasons Y and Z.

Some time later

E: Oops, turns out there was a mistake in my experiment, the sign on constant X should really be negative.

T: It's even easier to see why that should be the case.