FUSE Spectra of the Black Hole Binary LMC X-3

TL;DR

This study presents far-ultraviolet spectra of LMC X-3, revealing stable O VI emission lines and their velocity variations, which offer new constraints on the black hole's mass during a high X-ray luminosity state.

Contribution

It provides the first detailed FUV spectral analysis of LMC X-3, linking emission line velocities to the black hole's orbital motion and mass estimation.

Findings

O VI emission lines are stable during observations.

Velocity variations align with the black hole's orbital velocity.

System was in a high X-ray luminosity state during data collection.

Abstract

Far-ultraviolet spectra of LMC X-3 were taken covering photometric phases 0.47 to 0.74 in the 1.7-day orbital period of the black-hole binary (phase zero being superior conjunction of the X-ray source). The continuum is faint and flat, but appears to vary significantly during the observations. Concurrent RXTE/ASM observations show the system was in its most luminous X-ray state during the FUSE observations. The FUV spectrum contains strong terrestrial airglow emission lines, while the only stellar lines clearly present are emissions from the O VI resonance doublet. Their flux does not change significantly during the FUSE observations. These lines are modelled as two asymmetrical profiles, including the local ISM absorptions due to C II and possibly O VI. Velocity variations of O VI emission are consistent with the orbital velocity of the black hole and provide a new constraint on its mass.