CAMPANA, SergioSergioCAMPANA2020-05-262020-05-2620160028-0836http://hdl.handle.net/20.500.12386/25187Two sources of highly energetic flares have been discovered in archival X-ray data of 70 nearby galaxies. These flares have an undetermined origin and might represent previously unknown astrophysical phenomena. See Letter p.356STAMPAenArticle10.1038/538321a2-s2.0-84992406210000386673100024https://www.nature.com/articles/538321a2016Natur.538..321CFIS/05 - ASTRONOMIA E ASTROFISICAERC sectors::Physical Sciences and Engineering::PE9 Universe sciences: astro-physics/chemistry/biology; solar systems; stellar, galactic and extragalactic astronomy, planetary systems, cosmology, space science, instrumentation::PE9_11 Relativistic astrophysics