Read Spell TracesSource Ultimate Intrigue pg. 90
You can identify spells by the lingering traces they leave.
Benefit: When using identify or any spell of a higher level that normally allows you to detect the school and aura strength of an active spell, if you exceed the DC by 10 or more, you also learn the exact spell. If the spell you are using would already allow you to learn the exact spell from its aura, you can attempt to identify the spell from the traces in a lingering aura, though you take a –10 penalty on such an attempt. When using greater detect magic to attempt to identify unique magical signatures, you receive a +2 bonus on your Knowledge (arcana) checks.
In addition, you gain a +2 bonus on saving throws against magic aura and other spells and effects that conceal a spell’s true aura unless you succeed at a saving throw.