Combined analysis of neutron star natal kicks using proper motions and parallax measurements for radio pulsars and Be X-ray binaries

Abstract

Supernova explosion and the associated neutron star natal kicks are important events on a pathway of a binary to become a gravitational wave source, an X-ray binary or a millisecond radio pulsar. Weak natal kicks often lead to binary survival, while strong kicks frequently disrupt the binary. In this article, we aim to further constrain neutron star natal kicks in binaries. We explore binary population synthesis models by varying prescription for natal kick, remnant mass and mass accretion efficiency. We introduce a robust statistical technique to analyse combined observations of different nature. Using this technique, we further test different models using parallax and proper motion measurements for young isolated radio pulsars and similar measurements for Galactic Be X-ray binaries. Our best model for natal kicks is consistent with both measurements and contains a fraction of w = 0.2 ± 0.1 weak natal kicks with $\sigma _1 = 45^{+25}_{-15}$ km s−1, the remaining natal kicks are drawn from the high-velocity component, same as in previous works: σ2 = 336 km s−1. We found that currently used models for natal kicks of neutron stars produced by electron capture supernova (combination of maxwellian σ = 265 km s−1 and σ = 30 km s−1 for electron capture) are inconsistent or marginally consistent with parallaxes and proper motions measured for isolated radio pulsars. We suggest a new model for natal kicks of ecSN, which satisfy both observations of isolated radio pulsars and Be X-ray binaries.

Where are the magnetar binary companions? Candidates from a comparison with binary population synthesis predictions

“…Of the remaining 20, two have apparently stellar properties broadly consistent with expectations for bound companions (CXOU J1714 and SGR 0755, for which the bright star is a confirmed HMXB, but may but a chance alignment with the magnetar in question). consistent with the upper end of compact remnant-massive star bound systems, specifically high-mass X-ray binaries (Mirabel et al 2002;Atri et al 2019;Igoshev et al 2021). If we instead adopt a distance of 5 kpc -the lowest distance estimated for CXOU J1714 before it was revised upwards by association with the CTB 37 supernova remnant complex (Tian & Leahy 2012) -the transverse velocity estimate drops to 140 ± 67 kms −1 , entirely consistent with bound systems.…”

“…We also investigate the impact of assuming different neutron star natal kick velocities -the kick distributions of Hobbs et al (2005) and Igoshev (2020) yield very similar f bound values of 0.049 and 0.050. Igoshev et al (2021) also found little difference between these kicks in terms of the Be star mass distribution in X-ray binaries. The kick of Bray & Eldridge (2016, however, gives a substantially larger value of 0.23.…”

The role of supernova convection for the lower mass gap in the isolated binary formation of gravitational wave sources

“…Besides the stellar collapse and SN engine mechanism which is the main subject of this work, there are many other uncertain processes that dictate the formation of DCO mergers. Some examples of such processes or parameters which may significantly influence physical properties of DCO mergers are: the metallicity-specific star formation rate density and initial mass function (Chruślińska et al 2020;Santoliquido et al 2021;Broekgaarden et al 2021a;Briel et al 2021;Kroupa & Jerabkova 2021), stellar winds (Vink et al 2001;Sander et al 2022), convection and overshooting (Klencki et al 2021;Belczynski et al 2022), NS and BH natal kicks (Mandel et al 2021;Igoshev et al 2021), type and rate of mass transfer and the outcome of stable/unstable RLOF (Vinciguerra et al 2020;Howitt et al 2020;Bavera et al 2020;Vigna-Gómez et al 2022). The assumptions adopted for this work are described in Section 2.…”

Where are the magnetar binary companions? Candidates from a comparison with binary population synthesis predictions

“…We also investigate the impact of assuming different neutron star natal kick velocities -the kick distributions of Hobbs et al ( 2005 ) and Igoshev ( 2020 ) yield very similar f bound values of 0.049 and 0.050. Igoshev et al ( 2021 ) also found little difference between these kicks in terms of the Be star mass distribution in X-ray binaries. The kick of Bray & Eldridge ( 2016 ) and Bray & Eldridge ( 2018 ), ho we ver, gi ves a substantially larger value of 0.23.…”