What type of action is concentrating on Detect Magic?

Question

Detect magic has

Duration concentration, up to 1 min./level (D)

But nowhere is concentration clearly defined or the action required to concentrate on this spell.

There is concentration while casting a spell

To cast a spell, you must concentrate. If something interrupts your concentration while you’re casting, you must make a concentration check or lose the spell.

One way to consider this is that to benefit from detect magic you continue casting it for as long as you want to benefit from its effect. However since I know of no spell which provides an effect while casting it, clearly detect magic must be finished casting, otherwise it makes no sense.

The most logical way for this to work is its a standard action to concentrate on the spell, but its never actually said anywhere.

I have a similar question called Spells which require concentration such as detect magic, but it was never really answered to my satisfaction.

Answer 1

A Standard Action

Whenever you have to concentrate to maintain a spell effect, your character must use a Standard Action:

Concentration

The spell lasts as long as you concentrate on it. Concentrating to maintain a spell is a standard action that does not provoke attacks of opportunity. Anything that could break your concentration when casting a spell can also break your concentration while you’re maintaining one, causing the spell to end. See concentration.

You can’t cast a spell while concentrating on another one. Some spells last for a short time after you cease concentrating.

Answer 2

You are mixing the duration of "concentration" and concentration checks you do when casting a spell in hostile conditions.

These are two different things with the same name.