[thulldud]

The authors are probably comparing this to solar flares, in which we see the flare by EM (light) 8 minutes after it happens, but the associated coronal mass ejection which causes most of the disruption comes a couple of days later, because the light travels at lightspeed, and the plasma travels much slower.

Scale that up to interstellar distances and magnitudes, and the plasma front would strike centuries, not days, after the EM pulse (be that visible or gamma).

So that is already a lot of disbelief to have to suspend just to enjoy wasting a couple of hours in front of a movie screen.

[Joe Brower]

You are correct, of course. In the case of something like a supernova, the Earth would be burnt to a crisp and then many years later (hundreds of years most likely), the first outer shell of matter would arrive and make impact. That would finish off anything that managed to survive the initial EM burst.

Speaking of suspension of disbelief, I really had to check my BS-meter at the door when I went to see 'Avatar' -- from what I recall of EM theory. I loved the Pandora's floating rock formations, rich with "Unobtanium" ore (the room-temperature semiconductor central to the story). However, to make mountains float would require a magnetic field so intense it would pull the hemoglobin right out of your blood. That would have spoiled the movie a bit, I imagine... !