Potential kick velocity distribution of black hole X-ray binaries and implications for natal kicks

Abstract

We use Very Long Baseline Interferometry to measure the proper motions of three black hole X-ray binaries (BHXBs). Using these results together with data from the literature and Gaia-DR2 to collate the best available constraints on proper motion, parallax, distance and systemic radial velocity of 16 BHXBs, we determined their three dimensional Galactocentric orbits. We extended this analysis to estimate the probability distribution for the potential kick velocity (PKV) a BHXB system could have received on formation. Constraining the kicks imparted to BHXBs provides insight into the birth mechanism of black holes (BHs). Kicks also have a significant effect on BH-BH merger rates, merger sites, and binary evolution, and can be responsible for spin-orbit misalignment in BH binary systems. 75% of our systems have potential kicks > 70 km s −1 . This suggests that strong kicks and hence spin-orbit misalignment might be common among BHXBs, in agreement with the observed quasi-periodic X-ray variability in their power density spectra. We used a Bayesian hierarchical methodology to analyse the PKV distribution of the BHXB population, and suggest that a unimodal Gaussian model with a mean of 107±16 km s −1 is a statistically favourable fit. Such relatively high PKVs would also reduce the number of BHs likely to be retained in globular clusters. We found no significant correlation between the BH mass and PKV, suggesting a lack of correlation between BH mass and the BH birth mechanism. Our Python code allows the estimation of the PKV for any system with sufficient observational constraints.

Machine-learning interpolation of population-synthesis simulations to interpret gravitational-wave observations: A case study

“…Our results suggest that binary BHs were imparted moderate kicks at formation (σ 70 km/s). This is in tentative agreement with position and proper-motion measurements in X-ray binaries [41][42][43], as well as GW measurements of BH-binary spin misalignment [44,45]. Our findings are, however, in contrast with current supernova models which predict that BH natal kicks should be highly suppressed due to fallback material in the late stage of the explosion (e.g.…”

A period-dependent spatial scatter of Galactic black hole transients

“…This was based upon work done by Repetto et al (2012) using Galactic population simulations, accounting for a variety of kick distributions and the location of objects within the Galactic potential. More recent proxies of v nk for BHXBs fall around ∼ 80-130 km s −1 (Gandhi et al 2019;Atri et al 2019b), and this is also the case for the distribution inferred from the first set of more massive BHBs studied with LIGO/Virgo (Wong & Gerosa 2019). However, accounting for realistic initial spatial and kinematic scatter of progenitors in the disc can greatly mitigate the necessity of strong natal kicks in many cases (Belczynski et al 2016b), thus complicating proper evaluation of this scenario.…”

“…Some of these handicaps are being overcome with data from new astrometric surveys which are transforming the understanding of BHs in Galactic binary systems (e.g. Gaia Collaboration et al 2018;Gandhi et al 2019;Atri et al 2019b;Rao et al 2019). Here, we investigate updated samples of Galactic BHXBs to uncover an intriguing relation between the latitudinal height scatter and system orbital periods for BHXBs.…”

A radio parallax to the black hole X-ray binary MAXI J1820+070

“…We monitored MAXI J1820 (see Table 1) with the Very Long Baseline Array (VLBA), using both the Jet Acceleration and Collimation Probe of Transient X-ray Binaries (JACPOT-XRB) program (e.g., Miller-Jones et al 2012, and a longrunning astrometry program (e.g., Atri et al 2019, proposal code BA130), supplemented with a targeted European VLBI Network (EVN) campaign (proposal code EA062). All observations used a combination of J1821+0549 (J1821 hereon) and J1813+065 (J1813 hereon) as the phase reference and astrometric check sources.…”