Double and single recycled pulsars: an evolutionary puzzle?

Abstract

We investigate the statistics of isolated recycled pulsars and double neutron star binaries in the Galactic disk. Since recycled pulsars are believed to form through accretion and spinup in close binaries, the isolated objects presumably originate from disrupted progenitors of double neutron stars. There are a comparable number of double neutron star systems compared to isolated recycled pulsars. We find that standard evolutionary models cannot explain this fact, predicting several times the number of isolated recycled pulsars than those in double neutron star systems. We demonstrate, through population synthesis calculations, that the velocity distribution of isolated recycled pulsars is broader than for binary systems. When this is accounted for in a model for radio pulsar survey selection effects, which include the effects of Doppler smearing for the double neutron star binaries, we find that there is a small (25%) bias towards the detection of double neutron star systems. This bias, however, is not significant enough to explain the observational discrepancy if standard (sigma = 265 km/s) neutron star natal kick velocities are invoked in binary population syntheses. Population syntheses in which the 1D Maxwellian velocity dispersion of the natal kick is sigma=170 km/s are consistent with the observations. These conclusions further support earlier findings the neutron stars formed in close interacting binaries receive significantly smaller natal kicks than the velocities of Galactic single pulsars would seem to indicate.Comment: 12 pages, MNRAS (accepted

Massive double compact object mergers: gravitational wave sources and r-process element production sites

“…Other authors sometimes use a Maxwellian distribution with a similar average (e.g., following Hobbs et al 2005) but it can readily be understood that both treatments yield very similar results. Some recent results however point to lower velocities (e.g., Belczynski et al 2010b). To test the influence on our results, a calculation is presented with an average kick velocity of 265 km s −1 .…”

The Fate of the Compact Remnant in Neutron Star Mergers

“…But this initial NS mass can be larger by as much as 0.1 M e . In many cases, the first neutron star formed also goes through a common envelope phase where it can accrete up to ∼0.1 M e through hypercritical accretion (Fryer et al 1996;Belczynski et al , 2010bMacleod & Ramirez-Ruiz 2015a, 2015b.…”

Displacement of X-ray binaries: constraints on the natal kicks

“…For example, the value of σ kick is expected to be in excess of ∼100−200 km s −1 based on measurements of proper motions for isolated radio pulsars (Lyne & Lorimer 1994;Hansen & Phinney 1997;Cordes & Chernoff 1998;Arzoumanian et al 2002;Hobbs et al 2005), but is expected to be smaller based on recent observation of NSs found in binaries (on the order of 100 km s −1 , Pfahl et al 2002;Belczynski et al 2010b;Wong et al 2010;Bodaghee et al 2012) and BPS simulations (on the order of ∼150 km s −1 , Zuo et al 2014;Belczynski et al 2010b). I adopt σ kick = 150 km s −1 in the basic model (model BAC, see Table 1).…”

“…By comparing the predictions with the observed properties of sources interested, the natal kick can be properly constrained. Such works have been carried out extensively by several authors, such as Deway & Cordes (1987), Fryer & Kalogera (1997a,b), Fryer et al (1998), Belczynski et al (2010b) on single pulsars and/or double NS binaries, and Repetto et al (2012) on BH XRBs. For example, recently, Repetto et al (2012), by comparing the synthesized BH low-mass X-ray binary (LMXB) population with the Galactic distribution, concluded that BHs are most likely to have the same/similar distribution of kick velocities as NSs.…”