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Abstract: We investigate the statistics of isolated recycled pulsars and double neutronstar binaries in the Galactic disk. Since recycled pulsars are believed to formthrough accretion and spinup in close binaries, the isolated objects presumablyoriginate from disrupted progenitors of double neutron stars. There are acomparable number of double neutron star systems compared to isolated recycledpulsars. We find that standard evolutionary models cannot explain this fact,predicting several times the number of isolated recycled pulsars than those indouble neutron star systems. We demonstrate, through population synthesiscalculations, that the velocity distribution of isolated recycled pulsars isbroader than for binary systems. When this is accounted for in a model forradio pulsar survey selection effects, which include the effects of Dopplersmearing for the double neutron star binaries, we find that there is a small25% bias towards the detection of double neutron star systems. This bias,however, is not significant enough to explain the observational discrepancy ifstandard sigma = 265 km-s neutron star natal kick velocities are invoked inbinary population syntheses. Population syntheses in which the 1D Maxwellianvelocity dispersion of the natal kick is sigma=170 km-s are consistent with theobservations. These conclusions further support earlier findings the neutronstars formed in close interacting binaries receive significantly smaller natalkicks than the velocities of Galactic single pulsars would seem to indicate.

Author: K. Belczynski, D.R. Lorimer, J.P. Ridley, S.J. Curran



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