How would a beamed core antimatter drive appear from Earth?

[StrangerTides]

As I understand it, a beamed core antimatter drive would produce thrust by annihilating matter and antimatter and ejecting the results of the annihliation via a magnetic nozzle. The usable results would be charged pions, which would decay into muons, correct?

So my question is, if a spacecraft were approaching the solar system and using this type of propulsion system to decelerate (so that the nozzle is roughly aimed at Earth), would it be visible from an Earth-based telescope, and if so, how would it appear?

Thanks!

 

[Vanadium 50]

It would depend on how big it was, where it was and how fast it was going.

 

[StrangerTides]

Okay, let's just say it's small (say, the size of a small car), moving at a max of say 10% c, on a path intersecting the Earth, and decelerating, so the drive is aimed directly at the observer on the Earth. As for where it is, how about just beyond the orbit of the moon.

I guess my real question is whether anything produced by a matter-antimatter annihilation is visible, such as the pion beam itself, or any other byproducts.

Thanks.