Optical, ultraviolet and X-ray analysis of the black hole candidate BG Geminorum

We present the first high resolution optical spectrum of the black hole candidate BG Geminorum, as well as UV spectroscopy from the Hubble Space Telescope, and X-ray data from INTEGRAL. The UV spectra suggest the presence of material in BG Gem with velocities possibly as high as ∼1000 km s⁻¹, suggesting an origin at a distance of ∼0.7 R⊙ from a 3.5 M_⊙ object; if real, this would be strong evidence that the primary in BG Gem is indeed a black hole. In contrast, the upper limit provided by the INTEGRAL data gives a maximum X-ray luminosity of only ∼0.1 of the Eddington luminosity.