Critical Hit chance related questions

Hey guys, got a few more

1a. Does Azram's Star have a hidden Critical Hit chance bonus that is not in the weapon description?
1b. Does this Critical Hit chance increases with increased Magic Aptitude?

2. Does the Critical Hit chance bonus from Backstab Mastery universally applies to all throwing weapons, firearm weapons and bows even when not doing a proper backstab?
Or it only applies when you are doing a proper backstab when standing behind the enemy and holding the appropriate melee weapon?

 

Throwing mastery confers a critical hit bonus, that is all I know.