Confirming NGC 6231 as the parent cluster of the runaway high-mass X-ray binary HD 153919/4U 1700-37 withGaiaDR2

Abstract

Context. A significant fraction (10–20%) of the most massive stars move through space with a high (v ≳ 30 km s−1) velocity. One of the possible physical explanations is that a supernova in a compact binary system results in a high recoil velocity of the system. If the system remains bound, it can be subsequently observed as a spectroscopic binary (SB1), a high-mass X-ray binary, a compact binary, and finally a gravitational-wave event. Aims. If such a system is traced back to its parent cluster, binary evolution models can be tested in great detail. Methods. The Gaia proper motions and parallaxes are used to demonstrate that the high-mass X-ray binary HD 153919/4U 1700-37 originates from NGC 6231, the nucleus of the OB association Sco OB1. Results. The O supergiant and its compact companion, of which the physical nature (a neutron star or a black hole) is unknown, move with a space velocity of 63 ± 5 km s−1 with respect to NGC 6231. The kinematical age of the system is 2.2 ± 0.1 Myr. The parallaxes and accurate proper motions in Gaia DR2 were used to perform a membership analysis of NGC 6231; 273 members are identified, of which 268 have good quality photometry. The distance to NGC 6231 is 1.63 ± 0.15 kpc. Isochrone fitting results in an age of 4.7 ± 0.4 Myr and an extinction AV to the cluster of 1.7 ± 0.1. With the identification of NGC 6231 as the parent cluster, the upper limit on the age of the progenitor of 4U1700-37 at the moment of the supernova explosion is 3.0 ± 0.5 Myr. Conclusions. With these constraints, the evolutionary history of the system can be reconstructed with an initial mass of the progenitor of the compact object > 60 M⊙. The high mass, the extreme mass ratio, and short orbital separation of the system make it difficult to produce possible progenitor systems through population synthesis. We propose that the system experienced a Case A mass transfer phase before the supernova, which typically widens a binary. In order to create a progenitor system that does not merge, a lot of angular momentum must be lost from the system during the phase of mass transfer and/or an asymmetry in the supernova explosion provides a kick resulting in the observed orbital parameters. Given its current high space velocity and the derived evolutionary history, the compact object in the system is more likely to have received a large natal kick, which suggests that it is more likely a neutron star than a black hole. HD 153919/4U1700-37 might be a prototype in the Milky Way for the progenitor of gravitational wave events such as GW190412.

Finding the birthplace of HMXBs in the Galaxy using Gaia EDR3: Kinematical age determination through orbit integration

“…4U 1700-377 Ankay et al (2001) suggest that this HMXB originates from the OB association of Sco OB1, of which NGC 6231 is the core. This is based on astrometric data from Hipparcos, and more recent data from Gaia DR2 corroborates this finding (van der Meij et al 2021). The companion star in 4U 1700-377 is an early supergiant (O6 Ia, Sota et al 2011) weighing 46±5 M (Abubekerov 2004).…”

“…Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. Software: matplotlib (Hunter 2007), NumPy (van der Walt et al 2011), scipy (Jones et al 2001 and Python from python.org…”

No Peaks without Valleys: The Stable Mass Transfer Channel for Gravitational-wave Sources in Light of the Neutron Star–Black Hole Mass Gap

“…One would thus expect the birth rate of WR-XRB systems to be approximately equal to the birth rate of high-mass XRBs. However, while there are hundreds of Galactic high-mass XRBs (see Liu et al 2006, for the most recent review), there is only one known WR-XRB system in the Milky Way (Cygnus X-3; van Kerkwijk et al 1992). This is known as the "missing WR-XRB" problem (e.g., Lommen et al 2005).…”

“…On the other hand, if a dearth of low-mass BHs remains in all mass observations of BHs, we argue that a gap in the remnant mass distribution is a more likely explanation. A rapidly increasing number of recent detections through various observational methods already seem to challenge whether the NS-BH mass gap is empty (e.g., Breivik et al 2019;Giesers et al 2019;Thompson et al 2019;Rivinius et al 2020;Wyrzykowski & Mandel 2020;Gomez & Grindlay 2021;Jayasinghe et al 2021;van der Meij et al 2021;Andrews et al 2022;Jayasinghe et al 2022;Lam et al 2022;Sahu et al 2022). At the same time, many of these candidates are controversial (see El-Badry et al 2022, and references therein), and the existence of a gap in the remnant mass distribution remains an open question to this day.…”

No peaks without valleys: The stable mass transfer channel for gravitational-wave sources in light of the neutron star-black hole mass gap

“…On the other hand, if a dearth of low-mass BHs remains in all massobservations of BHs, we argue that a gap in the remnant mass distribution is a more likely explanation. A rapidly increasing number of recent detections through various observational methods already seem to challenge whether the NS-BH mass gap is empty (e.g., Thompson et al 2019;Giesers et al 2019;Breivik et al 2019;Rivinius et al 2020;Wyrzykowski & Mandel 2020;Gomez & Grindlay 2021;Sahu et al 2022;Lam et al 2022;van der Meij et al 2021;Jayasinghe et al 2021Jayasinghe et al , 2022Andrews et al 2022). At the same time, many of these candidates are controversial (see El-Badry et al 2022, and references therein), and the existence of a gap in the remnant mass distribution remains an open question to this day.…”