Speaker: Guillermo Rodriguez (INAF - Osservatorio Astronomico di Roma)
Title: Ultraluminous X-ray Sources: an expected population of Intermediate Mass Black Holes appears to be Super-Eddington Neutron Stars
Abstract: Ultraluminous X-ray Sources (ULXs) were thought to host a population of Intermediate or Stellar Mass Black Holes (IMBH, SMBH), but the recent discovery of several Pulsating Ultra Luminous X-rays sources (PULXs) challenges this view. PULXs unambiguously associates these sources to Neutron Stars (NSs) exceeding up to 1000 times their (isotropic) Eddington Luminosity. This findings also challenge the standard, currently used accretion models. Having a clear picture of the PULX population is crucial to understand this new class of extragalactic NSs, the ULX class in general and the IMBH and SMBH populations in the Universe. The extreme timing properties and very low pulsed-fractions of the PULXs makes their discovery extremely challenging. I will tell you how we have made these discoveries and their main implications.