A.T. Robertson Commentary Luke 2:9

"And an angel of the Lord stood by them, and the glory of the Lord shone round about them: and they were sore afraid." — Luke 2:9 (ASV)

Stood by them (επεστη αυτοις). Ingressive aorist active indicative. Stepped by their side. The same word in Ac 12:7 of the angel there. Paul uses it in the sense of standing by in Ac 22:20. It is a common old Greek word, εφιστημ.

Were sore afraid (εφοβηθησαν φοβον μεγαν). First aorist passive indicative with cognate accusative (the passive sense gone), they feared a great fear.