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16 April 2024 |
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Isolated Neutron Stars in the Galaxy | | S.B. Popov
; M.E. Prokhorov
; M. Colpi
; A. Treves
; R. Turolla
; V.M. Lipunov
; | | Date: |
14 Aug 2000 | | Subject: | astro-ph | | Affiliation: | Sternberg Astronomical Institute), M.E. Prokhorov (Sternberg Astronomical Institute), M. Colpi (University of Milan), A. Treves (University of Como), R. Turolla (University of Padova) and V.M. Lipunov (Moscow State University | | Abstract: | In this article we briefly review our recent results on evolution and properties of isolated neutron stars (INSs) in the Galaxy. As the first step we calculate a {it census} of INSs in our Galaxy. We infer a lower bound for the mean kick velocity of NSs, $ sim $(200-300) ${
m km s^{-1}}$. The same conclusion is reached for both a constant magnetic field ($Bsim 10^{12}$ G) and for a magnetic field decaying exponentially with a timescale $sim 10^9$ yr. These results, moreover, constrain the fraction of low velocity stars, which could have escaped pulsar statistics, to $sim$few percents. Then we show that the range of minimum value of magnetic moment, $mu_b$: $sim 10^{29.5}ge mu_b ge 10^{28} {
m G} {
m cm}^3$, and the characteristic decay time, $t_d$: $sim 10^8ge t_d ge 10^7 {
m yrs}$, can be excluded assuming the standard initial magnetic momentum, $mu_0=10^{30} {
m G} {
m cm}^3$, 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 $mu_0$. It is shown that old accreting INSs become more abundant than young cooling INSs at X-ray fluxes below $sim 10^{-13}$ erg cm$^{-2}$ s$^{-1}$. We can predict that about one accreting INS per square degree should be observed at the {it Chandra} and {it Newton} flux limits of $sim 10^{-16}$ erg cm$^{-2}$ s$^{-1}.$ The weak {it ROSAT} sources, associated with INSs, can be young cooling objects, if the NSs birth rate in the solar vicinity during the last $sim 10^6$ yr was much higher than inferred from radiopulsar observations. | | Source: | arXiv, astro-ph/0008199 | | Services: | Forum | Review | PDF | Favorites | |
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