Understanding Compact Object Formation and Natal Kicks. Iii. The Case of Cygnus X-1

Abstract

In recent years, accurate observational constraints become available for an increasing number of Galactic X-ray binaries. Together with proper motion measurements, we could reconstruct the full evolutionary history of X-ray binaries back to the time of compact object formation. In this paper, we present the first study of the persistent X-ray source Cygnus X-1 that takes into account of all available observational constraints. Our analysis accounts for three evolutionary phases: orbital evolution and motion through the Galactic potential after the formation of black hole (BH), and binary orbital dynamics at the time of core collapse. We find that the mass of the BH immediate progenitor is 15.0 − 20.0 M ⊙ , and at the time of core collapse, the BH has potentially received a small kick velocity of ≤ 77 km s −1 at 95% confidence. If the BH progenitor mass is less than ∼ 17 M ⊙ , a non zero natal kick velocity is required to explain the currently observed properties of Cygnus X-1. Since the BH has only accreted mass from its companion's stellar wind, the negligible amount of accreted mass is impossible to explain the observationally inferred BH spin of a * > 0.95, and the origin of this extreme BH spin must be connected to the BH formation itself. Right after the BH formation, we find that the BH companion is a 19.8 − 22.6 M ⊙ main sequence star, orbiting the BH at a period of 4.7 − 5.2 days. Furthermore, recent observations show that the BH companion is currently super-synchronized. This supersynchronism indicates that the strength of tides exerted on the BH companion should be weaker by a factor of at least two compared to the usually adopted strength.

Black Hole Spin via Continuum Fitting and the Role of Spin in Powering Transient Jets

“…Consider, for example, the persistent system Cyg X-1 ): For its black hole to achieve its present spin of a * > 0.95 via disk accretion, an initially nonspinning black hole would have had to accrete > 7.3 M ⊙ from its donor (Bardeen 1970;King & Kolb 1999) to become the 14.8 M ⊙ black hole we observe today. However, even at the maximum (Eddington-limited) accretion rate this would require > 31 million years, while the age of the system is between 4.8 and 7.6 million years (Wong et al 2012). Likewise for M33 X-7 and LMC X-1, the corresponding minimum spin-up timescales are > 17 and > 25 million years, respectively, while the respective ages of the systems are < ∼ 3 and < ∼ 5 million years .…”

“…Initial efforts are under way to use the available continuum-fitting spin data to investigate the formation and evolution of black holes, as well as their host systems (e.g., Lee et al 2002;Wong et al 2012), and to understand how a black hole interacts with its environment (e.g., Wang et al 2003;Cooke et al 2008). The most important application to date of spin data is the discovery of a long-predicted correlation between jet power and black hole spin, which is the subject of Section 7.…”

Compact Binary Merger Rates: Comparison With Ligo/Virgo Upper Limits

“…Natal Kick from 3D Velocity: Cyg X-1 Wong et al (2012) have studied evolution and dynamics of 3D motion of Cyg X-1 based on parallax measurement of Reid et al (2011). They have used the same method as Willems et al (2005) and Fragos et al (2009) in study of GRO J1655-40 and XTE J1118+480, respectively.…”

“…They have used the same method as Willems et al (2005) and Fragos et al (2009) in study of GRO J1655-40 and XTE J1118+480, respectively. Using position of this system in Galaxy, its radial velocity and its proper motion Wong et al (2012) traced this system back in time to the moment of BH formation. The system was found to be h z = 30-110 pc above Galactic plane and move with peculiar 3D velocity of 22-32 -km s 1 right after BH formation.…”

Estimates of black hole natal kick velocities from observations of low-mass X-ray binaries

“…Willems et al (2005) find that a birth kick of a few tens of km/s (and no more than around 200 km/s) was given in the supernova that formed GRO J1655-40. Wong et al (2012) find that Cygnus X-1 likely received a non-zero birth kick (cf. (Nelemans et al 1999)), but with a velocity no larger than around 80 km/s.…”