Multi-wavelength spectroscopic analysis of the ULX Holmberg II X-1 and its nebula suggests the presence of a heavy black hole accreting from a B-type donor

S. Reyero Serantes, L. Oskinova, W. -R. Hamann +11

Ultra-luminous X-ray sources (ULXs) are high-mass X-ray binaries with an X-ray luminosity above $10^{39}$ erg s${}^{-1}$. These ULXs can be powered by black holes that are more massi…