The elusiveness of old neutron stars

被引:27
作者
Colpi, M
Turolla, R
Zane, S
Treves, A
机构
[1] Univ Milan, Dept Phys, I-20133 Milan, Italy
[2] Univ Padua, Dept Phys, I-35131 Padua, Italy
[3] Scuola Int Super Studi Avanzati, I-34014 Trieste, Italy
[4] Univ Milan, Fac Sci 2, I-22100 Como, Italy
关键词
accretion; accretion disks; stars : neutron; X-rays : stars;
D O I
10.1086/305810
中图分类号
P1 [天文学];
学科分类号
0704 ;
摘要
Old neutron stars (ONSs) that have radiated away their internal and rotational energy may still shine if they are accreting the interstellar medium. Despite their large number, only two promising candidates have been detected so far, and rather stringent limits on their observability follow from the analysis of ROSAT surveys. This contrasts with optimistic theoretical estimates that predicted a large number of sources in ROSAT fields. We have reconsidered the issue of the observability of ONSs, accounting for the spin and magnetic field evolution over the neutron star lifetime. In the framework of a spin-induced held decay model, we show that the total number of ONSs that are at present in the accretion stage is reduced by a factor of similar to 5 over previous figures if the characteristic timescale for crustal current dissipation is similar to 10(8)-10(9) yr. This brings theoretical predictions much closer to observational limits. Most ONSs should be, at present, in the propeller phase; if subject to episodic flaring, they could be observable.
引用
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页码:252 / 257
页数:6
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