How long can afterglow last after a fireball?
This is an persistent ionization trail. As the meteoroid goes through the upper atmosphere at high speed (sometimes more than 45km/s) electrons are stripped from atoms. As the electrons recombine, the gas glows.

Persistent trails are formed by brighter meteors, and can be visible to the naked eye. They may be visible for up to about 45 minutes, but that depends on the meteor. Generally brighter meteors have brighter trails. 

The movement and streaking in the trail can reveal the presence of upper atmosphere winds. As radio waves bounce off the ionised trails, they can be used for long distance radio communictions.

Persistent trails were discussed by the "Bad Astronomer" 



Image taken during the 1966 Leonid Meteor storm, produced by a Mag -6 meteor