(S (S (BASENP (DT The) (NN explosion)) (VP (VBZ is) (VP (VBN said) (S (VP (TO to) (VP (VB be) (NP (NP (BASENP (DT the) (ADJP (RBS most) (JJ powerful)) (NN explosion)) (VP (VBN known) (PP (TO to) (BASENP (NNS scientists))))) (COMMA ,) (SBAR (WHNP (WDT which)) (S (VP (VBZ consists) (PP (IN of) (NP (BASENP (DT a) (JJ gamma-ray) (NN burst)) (CC or) (BASENP (DT an) (JJ x-ray) (NN blast)))))))))))))) (PERIOD .))