(S (S (S (BASENP (DT The) (NNS clouds)) (VP (VBD were) (VP (VBN detected) (S (VP (VBG using) (BASENP (NNP Chandra) (NNS observations))))))) (SBAR (WHADVP (WRB when)) (S (BASENP (DT the) (NN galaxy) (NNP Mkn) (NNP 421)) (VP (VBD brightened) (PP (IN in) (BASENP (NN X-ray) (NNS emissions))))))) (PERIOD .))