The mass of the black hole in GS2023+338/V404 Cygni

Abstract

New high resolution (0.8 A) Hα spectroscopy provides further constraints on the orbital parameters of the black hole candidate V404 Cyg. Our updated mass function is now 6.08±0.06 M⊙ which confirms V404 Cyg as the most important black hole candidate yet found. We also resolve the rotational broadening of the secondary star which yields the lowest mass ratio ever measured (q=Mc/Mx=0.050). The mass of the black hole is now restricted to the range 7–29 M⊙.