The Velocity Distribution of Isolated Radio Pulsars

Abstract

(Abridged) We infer the velocity distribution of radio pulsars by modelling their birth, evolution, and detection in large-scale 0.4 GHz pulsar surveys, and by comparing model distributions of measurable pulsar properties with survey data using a likelihood function. We test models that characterize a population's birth rate, luminosity, shutoff of radio emission, birth locations, and birth velocities. We infer that the radio beam luminosity (i) is comparable to the energy flux of relativistic particles in models for spin-driven magnetospheres, signifying that radio emission losses reach nearly 100% for the oldest pulsars; and (ii) scales approximately as sqrt(Edot) which, in magnetosphere models, is proportional to the voltage drop available for acceleration of particles. We find that a two-component velocity distribution with characteristic velocities of 90 km/s and 500 km/s is greatly preferred to any one-component distribution. We explore some consequences of the preferred birth velocity distribution: (i) roughly 50% of pulsars in the solar neighborhood will escape the Galaxy, while ~15% have velocities greater than 1000 km/s; (ii) an important low-velocity population exists that increases the fraction of neutron stars retained by globular clusters and is consistent with the number of old objects that accrete from the interstellar medium; (iii) under standard assumptions for supernova remnant expansion and pulsar spin-down, ~10% of pulsars younger than 20 kyr will appear to lie outside of their host remnants. Finally, we comment on the ramifications of our birth velocity distribution for binary survival and the population of inspiraling binary neutron stars relevant to some GRB models and potential sources for LIGO.Comment: 16 pages, 4 figures, ApJ (in press). Revisions to reflect refereed version include a new sub(sub)section on effects of the 'standard candle" assumption, and a revised Figure 2. Essential results unchange

Strange exotic states and compact stars

“…So pulsars are speeding through our Galaxy! We note in passing that the distribution of pulsar kick velocities has been found in some earlier work to be bimodal [36] which has been connected to the coexistence of neutron stars and quark stars by Bombaci and Popov [37], where the quark stars experience a second kick due to the phase transition from hadronic to quark matter (see also [38]). …”

Binary star progenitors of long gamma-ray bursts

“…The specific angular momentum of the least stable orbit around a 3 M Kerr black hole for these models is about 30 × 10 15 cm 2 s −1 . (Arzoumanian et al 2002). In order to estimate the chance of obtaining a runaway star out of our system we performed a Monte Carlo simulation for a randomly oriented supernova kick.…”

“…In order to estimate the chance of obtaining a runaway star out of our system we performed a Monte Carlo simulation for a randomly oriented supernova kick. According to the observed velocity distribution of radio pulsars (Arzoumanian et al 2002) the probability for the binary system to break up by the first supernova explosion is about 80%. The same binary model as discussed above was also computed with α SM = 0.1 and α SM = 0.01.…”

Population statistics study of radio and gamma-ray pulsars in the Galactic plane

“…For the radio luminosity, we assume that radio pulsars are standard candles and follow the prescription of Arzoumanian, Chernoff & Cordes [1] (ACC) given by the expression…”

“…We follow the geometric model of the core beam in ACC [1] and the cone model of Kijak & Gil [16] described in this meeting by Harding, Grenier, & Gonthier [12]. In the study of ACC, the ratio of the core-to-cone peak fluxes had a P −1 dependence, resulting in a dominance of the core component for short period pulsars.…”