Confirming NGC 6231 as the parent cluster of the runaway high-mass X-ray
  binary HD 153919/4U 1700-37 with Gaia DR2
  A significant fraction of the most massive stars move through space with a
high 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. If such a system is traced back to its parent
cluster, binary evolution models can be tested in great detail. The Gaia proper
motions and parallaxes are used to demonstrate that the high-mass X-ray binary
HD153919/4U 1700-37 originates from NGC6231, the nucleus of the OB association
Sco OB1. 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 km/s with respect to NGC6231. The kinematical age of the system is 2.2
Myr. The parallaxes and accurate proper motions in Gaia DR2 were used to
perform a membership analysis of NGC 6231. The distance to NGC6231 is 1.63 kpc.
Isochrone fitting results in an age of 4.7 Myr. With the identification of
NGC6231 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 Myr. With these
constraints, the evolutionary history of the system can be reconstructed with
an initial mass of the progenitor of the compact object >60 Msun. 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.
HD153919/4U1700-37 might be a prototype in the Milky Way for the progenitor of
gravitational wave events such as GW190412
