Explosive journal on Van Gogh discovered (10)
I believe the answer is:
incendiary
'explosive' is the definition.
'journal on van gogh discovered' is the wordplay.
'journal' becomes 'diary' (synonyms).
'on' is a charade indicator (letters next to each other).
'van gogh' becomes 'vincent' (synonyms).
'discovered' indicates the central letters.
The central letters of 'vincent' are 'incen'.
'diary' put after 'incen' is 'INCENDIARY'.
(Other definitions for incendiary that I've seen before include "bomb" , "Fire-raiser" , "of a provocative nature" , "Likely to stir up trouble" , "getting people excited" .)