ἆρ' οὖν; -> so then?
The particle ἆρα introduces "yes" or "no" questions. The particle οὖν is used "in dialogue (often in questions), to indicate that the point the speaker makes, the question the speaker asks, etc., is the main thing the speaker wants to convey or ask, given the preceding context (so, now, well then, therefore);
- in dialogue: τί οὖν; so what?, what, then?"
(Cambridge Grammar of Classical Greek , p. 681)