Suppose there is a device in the middle of a large but ordinary room that creates a permanent anti-magic field with a 10-foot radius (as per the Antimagic Field spell). A spellcaster suspects that the device is magical, so she casts Detect Magic (60 foot range, cone-shape) while standing 30 feet away.
Would the spellcaster detect the presence of the antimagic field, and does it depend on whether the field is from a magical item vs. cast by a spellcaster?
We know that the Detect Magic spell gets cast successfully because the caster is outside of the antimagic field. Presumably, whether or not the antimagic field gets detected depends on whether or not the antimagic field has an aura that extends past its radius. If the device had a 1 foot magical aura, then the Detect Magic spell would presumably not be able to detect the tiny aura because it couldn't penetrate into the antimagic field.
Another question is whether a magical aura is itself suppressed by an antimagic field, and whether an antimagic field itself produces any aura.
Note: this other question is extremely relevant, but does not discuss my particular question: Do you know that Detect Magic is being suppressed if it intersects with Antimagic Field?