Ultraviolet observations of the X-ray photoionized wind of Cygnus X-1 during X-ray soft/high state

Abstract

(Shortened) Ultraviolet observations of the black hole X-ray binary Cygnus X-1 were obtained using the STIS on HSTubble. We detect P Cygni line features show strong, broad absorption components when the X-ray source is behind the companion star and noticeably weaker absorption when the X-ray source is between us and the companion star. We fit the P Cygni profiles using the SEI method applied to a spherically symmetric stellar wind subject to X-ray photoionization from the black hole. The Si IV doublet provides the most reliable estimates of the parameters of the wind and X-ray illumination. The velocity $v$ increases with radius $r$ according to $v=v_{\infty }(1-r_{\star }/r{)}^{\beta }$, with$\beta \approx 0.75$ and $v_{\infty }\approx 1420$ km s${}^{-1}$.The microturbulent velocity was $\approx 160$ km s${}^{-1}$. Our fit implies a ratio of X-ray luminosity to wind mass-loss rate of L${}_{X,38}/{\dot{M}}_{-6}\approx 0.33$, measured at ${\dot{M}}_{-6}$ = 4.8. Our models determine parameters that may be used to estimate the accretion rate onto the black hole and independently predict the X-ray luminosity. Our predicted L${}_x$ matches that determined by contemporaneous RXTE ASM remarkably well, but is a factor of 3 lower than the rate according to Bondi-Hoyle-Littleton spherical wind accretion. We suggest that some of the energy of accretion may go into powering a jet.

34 pages, 21 figures, 4 tables, accepted for publication in ApJ

References in corpus (1)

• Stellar Wind Variations During the X-ray High and Low States of Cygnus X-1

Cited by in corpus (2)

• Chandra X-ray spectroscopy of the focused wind in the Cygnus X-1 system. I. The non-dip spectrum in the low/hard state
• Stellar Wind Variations During the X-ray High and Low States of Cygnus X-1