Evolution of Isolated Neutron Stars

Abstract. In this paper we briefly review our recent results on evolution and properties of isolated neutron stars (INSs) in the Galaxy. As the first step we discuss stochastic period evolution of INSs. We briefly discuss how an INS’s spin period evolves under influence of interaction with turbulized interstellar medium. To investigate statistical properties of the INS population we calculate a census of INSs in our Galaxy. We infer a lower bound for the mean kick velocity of NSs, < V >∼(200-300) kms. The same conclusion is reached for both a constant magnetic field (B ∼ 10 G) and for a magnetic field decaying exponentially with a timescale ∼ 10 yr. These results, moreover, constrain the fraction of low velocity NSs, which could have escaped pulsar statistics, to ∼few percents. Then we show that for exponential field decay the range of minimum value of magnetic moment, μb: ∼ 10 29.5 ≥ μb ≥ 10 28 Gcm, and the characteristic decay time, td: ∼ 10 8 ≥ td ≥ 10 7 yrs, can be excluded assuming the standard initial magnetic momentum, μ0 = 10 30 Gcm, if accreting INSs are observed. For these parameters an INS would never reach the stage of accretion from the interstellar medium even for a low space velocity of the star and high density of the ambient plasma. The range of excluded parameters increases for lower values of μ0. It is shown that old accreting INSs become more abundant than young cooling INSs at X-ray fluxes below ∼ 10 erg cm s. We can predict that about one accreting INS per square degree should be observed at the Chandra and Newton flux limits of ∼ 10 erg cm s. The weak ROSAT sources, associated with INSs, can be young cooling objects, if the NSs birth rate in the solar vicinity during the last ∼ 10 yr was much higher than inferred from radiopulsar observations.