Populating the Galaxy with pulsars I. Stellar and binary evolution

Abstract

The computation of theoretical pulsar populations has been a major component of pulsar studies since the 1970s. However, the majority of pulsar population synthesis has only regarded isolated pulsar evolution. Those that have examined pulsar evolution within binary systems tend to either treat binary evolution poorly or evolve the pulsar population in an ad hoc manner. Thus, no complete and direct comparison with observations of the pulsar population within the Galactic disc has been possible to date. Described here is the first component of what will be a complete synthetic pulsar population survey code. This component is used to evolve both isolated and binary pulsars. Synthetic observational surveys can then be performed on this population for a variety of radio telescopes. The final tool used for completing this work will be a code comprised of three components: stellar/binary evolution, Galactic kinematics and survey selection effects. Results provided here support the need for further (apparent) pulsar magnetic field decay during accretion, while they conversely suggest the need for a re-evaluation of the assumed typical millisecond pulsar formation process. Results also focus on reproducing the observed PṖ diagram for Galactic pulsars and how this precludes short time-scales for standard pulsar exponential magnetic field decay. Finally, comparisons of bulk pulsar population characteristics are made to observations displaying the predictive power of this code, while we also show that under standard binary evolutionary assumption binary pulsars may accrete much mass.

Accretion, ablation and propeller evolution in close millisecond pulsar binary systems

“…For our base model (Model A) accretion induced field decay is chosen to follow an inverse function (equ. 9 of Kiel et al 2008) with a scaling factor of M ⋆ = 10 −4 M ⊙ (Shibazaki et al 1989) and a pulsar magnetic field decay timescale of 900 Myr. This form of decay is adopted as the overall shape of the theoretical pulsar distribution better reproduces the observed distribution of pulsars in the spin period-spin period derivative diagram than equ.…”

“…This form of decay is adopted as the overall shape of the theoretical pulsar distribution better reproduces the observed distribution of pulsars in the spin period-spin period derivative diagram than equ. 8 of Kiel et al (2008). Three supernova Maxwellian kick distributions are adopted which correspond to core collapse (with a dispersion of σ CC = 265 km s −1 ), accretion induced collapse (σ AIC = 90 km s −1 ), and electron capture (as defined by Kiel et al 2008; σ ECS = 90 km s −1 ).…”

“…binpop employs a rapid Binary Stellar Evolution (bse) algorithm as described in Hurley, Tout & Pols (2002) 1 and Hurley, Pols & Tout (2000), with updates provided in Kiel & Hurley (2006), Kiel et al (2008) and Kiel & Hurley (2009). An important addition to bse, for this work, was the inclusion of pulsar physics in both isolation and binary systems (Kiel at al.…”

“…The binary population synthesis is performed using binpop, a package developed in Kiel et al (2008). binpop employs a rapid Binary Stellar Evolution (bse) algorithm as described in Hurley, Tout & Pols (2002) 1 and Hurley, Pols & Tout (2000), with updates provided in Kiel & Hurley (2006), Kiel et al (2008) and Kiel & Hurley (2009).…”

“…In this process, the propeller mechanism expels incoming material at the expense of the NS's angular momentum. During this phase the NS spin angular momentum and orbital angular momentum are updated as described by Kiel et al (2008) and outlined below. In this case, the donor spins down as ∆M is removed, coupling it to the orbit as described above.…”