A participle of attendant circumstance is translated as a finite verb in parallel with the main verb of the sentence. GGBB gives five characteristics of a participle of attendant circumstance:
The tense of the participle is usually aorist.
The tense of the main verb is usually aorist.
The mood of the main verb is usually imperative or indicative.
The participle will precede the main verb.
Attendant circumstance participles occur frequently in narrative literature, infrequently elsewhere. (GGBB 642)