A flash, perhaps, and a bang (6)
I believe the answer is:
report
I believe this is a double definition.
'a flash perhaps' is the first definition.
(flash is a kind of report)
'a bang' is the second definition.
(I've seen this before)
'and' acts as a link.
(Other definitions for report that I've seen before include "Relate; gun noise" , "Make a complaint about (someone)" , "Narrative given by porter" , "'Description, account (6)'" , "Written account" .)