Orbital period decay of compact black hole X-ray binaries: the influence of circumbinary disks?

Abstract

Context. Recently, compact black hole X-ray binaries XTE J 1118+480 and A0620-00 have been reported to be experiencing a fast orbital period decay, which is two orders of magnitude higher than expected with gravitational wave radiation. Magnetic braking of an Ap/Bp star has been suggested to account for the period change when the surface magnetic field of the companion star B s > ∼ 10 4 G. However, our calculation indicates that anomalous magnetic braking cannot significantly contribute to the large orbital period decay rates observed in these two sources even if B s > ∼ 10 4 G. Aims. Observations have provided evidence that circumbinary disks around two compact black hole X-ray binaries may exist. Our analysis shows that, for some reasonable parameters, tidal torque between the circumbinary disk and the binary can efficiently extract the orbital angular momentum from the binary, and result in a large orbital period change rate. Methods. Based on the circumbinary disk model, we simulate the evolution of XTE J 1118+480 via a stellar evolution code. Results. Our computations are approximatively in agreement with the observed data (the masses of two components, donor star radius, orbital period, and orbital period derivative). Conclusions. The mass transfer rate and circumbinary disk mass are obviously far greater than the inferred values from observations. Therefore, it seems that the circumbinary disk is unlikely to be the main cause of the rapid orbital decay observed in some compact black hole X-ray binaries.

Formation of Scorpius X-1 induced by anomalous magnetic braking of Ap/Bp stars

“…If the donor stars have a very strong magnetic field and a rel- atively high wind-driving efficiency, anomalously high orbitalperiod derivatives of black-hole LMXBs could be produced by anomalous magnetic braking (González Hernández et al 2017). In addition, circumbinary disks surrounding the binary may be an alternative mechanism as well (Chen & Li 2015;Chen & Podsiadlowski 2017 ).…”

Extremely fast orbital decay of the black hole X-ray binary Nova Muscae 1991

“…Recently, Chen & Li (2015) have proposed AML models including circumbinary discs as a possible way to explain the fast orbital period decays in these BHXBs. This work shows the evolution of orbital period and period derivative for XTE J1118+480 during ∼ 0.8 − 1.2 Gyr (for initial M2 ∼ 3 − 1.5 M⊙) of its binary evolution.…”

“…On the other hand, the detection of middleinfrared excesses from Spitzer (Muno & Mauerhan 2006) and WISE (Wang & Wang 2014) have been interpreted as evidence for the presence of candidate circumbinary discs, or Remillard (1986) jets (Gallo et al 2007), in these two BHXB systems. However, Chen & Li (2015) have presented AML models including circumbinary discs but found that both the required mass transfer rate and circumbinary disc mass are far greater than the values inferred from observations. This makes unlikely that circumbinary discs are the main cause of the rapid orbital decay observed in these two BHXBs.…”

A Circumbinary Disk Model for the Rapid Orbital Shrinkage in Black Hole Low-mass X-Ray Binaries

“…Theoretically it is possible to explain the rapid orbital shrinkage of the BHLMXBs with reasonable values of M CB,0 and t vis,0 . It is known that a rapid orbital decay can accelerate mass loss from the donor, consequently enhance the X-ray luminosity (Justham et al 2006;Chen & Li 2015). However, observationally the three BHLMXBs are all faint sources.…”

“…In this subsection, we present the results in the pre-CB disk phase by calculating a number of evolutions with different initial values of M 2 and P orb . Several authors have theoretically investigated the properties of the donors in BHLMXBs (e.g., Podsiadlowski et al 2003;Ivanova 2006;Justham et al 2006;Yungelson & Lasota 2008;Chen & Li 2015;Fragos & McClintock 2015;Wang et al 2016). In Table 1, We list the observed parameters of the three BHLMXBs.…”