X-ray Variations at the Orbital Period from Cygnus X-1 in the High/Soft State

Abstract

Orbital variability has been found in the X-ray hardness of the black hole candidate Cygnus X-1 during the soft/high X-ray state using light curves provided by the Rossi X-ray Timing Explorer's All Sky Monitor. We are able to set broad limits on how the mass-loss rate and X-ray luminosity vary between the hard and soft states. The folded light curve shows diminished flux in the soft X-ray band at phase 0 (defined as the time of of the superior conjunction of the X-ray source). Models of the orbital variability provide slightly superior fits when the absorbing gas is concentrated in neutral clumps and better explain the strong variability in hardness. In combination with the previously established hard/low state dips, our observations give a lower limit to the mass loss rate in the soft state (Mdot<2x10^{-6} Msun/yr) than the limit in the hard state (Mdot<4x10^{-6} Msun/yr). Without a change in the wind structure between X-ray states, the greater mass-loss rate during the low/hard state would be inconsistent with the increased flaring seen during the high-soft state.

Accepted for publication in The Astrophysical Journal

References in corpus (7)

• X-ray Properties of Black-Hole Binaries
• Probing clumpy stellar winds with a neutron star
• Chandra X-ray spectroscopy of the focused wind in the Cygnus X-1 system. I. The non-dip spectrum in the low/hard state
• The structure of blue supergiant winds and the accretion in supergiant High Mass X-ray Binaries
• The Ultraviolet Spectrum and Physical Properties of the Mass Donor Star in HD 226868 = Cygnus X-1
• Superorbital variability of X-ray and radio emission of Cyg X-1. I. Emission anisotropy of precessing sources
• Ultraviolet observations of the X-ray photoionized wind of Cygnus X-1 during X-ray soft/high state

Cited by in corpus (10)

• Long term variability of Cygnus X-1 V. State definitions with all sky monitors
• Long term variability of Cygnus X-1: VII. Orbital variability of the focussed wind in Cyg X-1 / HDE 226868 system
• A multiwavelength study of Cygnus X-1: the first mid-infrared spectroscopic detection of compact jets
• Chandra X-Ray Spectroscopy of the Focused Wind in the Cygnus X-1 System. II. The Nondip Spectrum in the Low/Hard State - Modulations with Orbital Phase
• Chandra X-ray spectroscopy of the focused wind in the Cygnus X-1 system III. Dipping in the low/hard state
• The X-ray spectral-timing contribution of the stellar wind in the hard state of Cyg X-1
• XRISM High-Resolution X-ray Spectroscopy of Cygnus X-1 -- highly ionized Iron absorption structures
• Orbital modulations of X-ray light curves of Cyg X-1 in its low/hard and high/soft states
• Stellar wind variability in Cygnus X-1 from high-resolution excess variance spectroscopy with Chandra
• Smearing of mass accretion rate variation by viscous processes in accretion disks in compact binary systems