ner_tags: O O O O O O O O O O O O O O O O B-Grant I-Grant I-Grant O B-Person O B-Person I-Person O O O O B-Instrument O O
tokens: We thank the anonymous referee for comments and suggestions. This paper was partially funded by the PRIN INAF 2014 grant. M.M. thanks M. Dadina for discussions about the X-IFU instrumental background.