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Population Synthesis of Old Neutron Stars in the Galaxy

Published online by Cambridge University Press:  25 May 2016

S. B. Popov ,
M. Colpi ,
A. Treves ,
R. Turolla ,
V. M. Lipunov  and
M. E. Prokhorov
S. B. Popov
Affiliation:
Sternberg Astronomical Institute, Universiteskii Pr. 13, 119899, Moscow, Russia
M. Colpi
Affiliation:
Dept. of Physics, Univ. of Milan, Via Celoria 16, 20133 Milan, Italy
A. Treves
Affiliation:
Dipartimento di Scienze, Univ. dell'Insubria, Via Lucini 3, 22100, Como, Italy
R. Turolla
Affiliation:
Dept. of Physics, Univ. of Padova, Via Marzolo 8, 35131 Padova, Italy
V. M. Lipunov
Affiliation:
Dept. of Physics, Moscow State Univ., Sternberg Astronomical Institute, Universiteskii Pr. 13, 119899, Moscow, Russia
M. E. Prokhorov
Affiliation:
Sternberg Astronomical Institute, Universiteskii Pr. 13, 119899, Moscow, Russia

Abstract

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The paucity of old, isolated accreting neutron stars in ROSAT observations is used to derive a lower limit on the mean velocity of neutron stars at birth. The secular evolution of the population is simulated following the paths of a statistical sample of stars for different values of the initial kick velocity, drawn from an isotropic, Gaussian distribution with mean velocity 0 ≤ 〈V〉 ≤ 550 km s−1. The spin-down, induced by dipole losses and the interaction with the ambient medium, is tracked together with the dynamical evolution in the Galactic potential, allowing for the determination of the fraction of stars which are, at present, in each of the four possible stages: Ejector, Propeller, Accretor, and Georotator. Taking from the ROSAT All-Sky Survey an upper limit of ~ 10 accreting neutron stars within ~ 140 pc from the Sun, we infer a lower bound for the mean kick velocity, 〈V〉 ≳ 200–300 km s−1. The same conclusion is reached for both a constant (B ~ 1012 G) and an exponentially decaying magnetic field with a timescale ~ 109 yr. Present results, moreover, constrain the fraction of low-velocity stars which could have escaped pulsar statistics to ≲ 1%.

Type
Part I: Talks
Information
Symposium - International Astronomical Union , Volume 195: Highly Energetic Physical Processes and Mechanisms , 2000 , pp. 181 - 188
Copyright
Copyright © Astronomical Society of the Pacific 2000 

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