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Session 113 - Neutron Stars & Pulsars.
Oral session, Saturday, January 10
International Ballroom East,

[113.08] The Unbiased Velocity Distribution of Neutron Stars from a Simulation of Pulsar Surveys

Z. Arzoumanian, J. M. Cordes, D. Chernoff (Cornell U.)

We present the results of a new simulation of the Galactic population of neutron stars: their birthrate, velocity distribution, luminosities, beaming characteristics, and spin evolution. The many simulations in the literature differ from one another primarily in their treatment of the selection effects associated with pulsar detection. Our method, the most realistic to date, goes beyond earlier efforts by retaining the full kinematic, rotational, luminosity, and beaming evolution of each simulated star: \beginitemize \item ``Monte-Carlo'' neutron stars are created according to assumed distributions (at birth) in spatial coordinates, kick velocity, and magnitudes and orientations of the spin and magnetic field vectors. \item The neutron stars spin down following an assumed braking law, and their Galactic trajectories are traced to the present epoch. \item For each star, a pulse waveform is generated using a phenomenological radio-beam model, obviating the need for an arbitrary beaming fraction. Luminosity is assumed to be a parameterized function of period and spin-down rate, with no intrinsic spread, and a parameterized death-line is applied. \item Interstellar dispersion and scattering consistent with survey instrumentation and the galactic locales of the neutron stars are applied to the pulse waveforms, which are Fourier analyzed and tested for detection following the techniques of real-world surveys. \enditemize A unique algorithm is used to compare the populations of simulated and known, non-millisecond, pulsars in the multi-dimensional space of observables (any subset of galactic coordinates, dispersion measure, period, spin-down rate, flux, and proper motion). Model parameters are varied, and statistically independent neutron star populations are created until a maximum likelihood model is found. The highlight of this effort is an unbiased determination of the velocity distribution of neutron stars. We discuss the implications of our results for supernova physics, binary evolution, and the nature of \gamma-ray transients.

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