gistfile1.lua

-- 1)
function enemy:shoot()
  local Bullet = require "Bullet";
  Bullet.owner = self;
  -- the same as your previous code
end;

function enemy:canShootAgain()
  self.activeBul = false;
end;

-- When you want the enemy to shoot again, just call canShootAgain from bullet
bullet.owner:canShootAgain();

gistfile2.lua

-- 2)
function enemy:shoot()
  local Bullet = require "Bullet";
  Bullet.owner = self;
  -- the same as your previous code
end;

function enemy:canShootAgain()
  self.activeBul = false;
end;

-- When you want the enemy to shoot again, just call canShootAgain from bullet
bullet.owner:dispatchEvent({name = 'canShootAgain'});

-- Add this to the end of your enemy construction
enemy:addEventListener('canShootAgain', enemy);

http://stackoverflow.com/questions/16391401/bullet-fire-reset-event-corona-sdk/16401418#16401418