On the minimum spin period of accreting pulsars

Sercan Çlklntoǧlu*, K. Yavuz Ekşi*

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1 Atıf (Scopus)

Özet

The distribution of the spin frequencies of neutron stars in low-mass X-ray binaries exhibits a cut-off at 730 Hz, below the break-up frequency (mass-shedding limit) of neutron stars. The absence of submillisecond pulsars presents a problem, given that these systems are older than the spin-up time-scale. We examine models of the disc-magnetosphere interaction near torque equilibrium balanced by the torque due to gravitational wave emission. We note that field lines penetrating the disc beyond the inner radius reduce the maximum rotation frequency of the star, a result well known since the seminal work of Ghosh & Lamb. We show that the polar cap area corresponds to about half the neutron star surface area at the cut-off frequency if the inner radius is slightly smaller than the corotation radius. We then include the change in the moment of inertia of the star due to the accretion of mass and find that this effect further reduces the maximum rotation frequency of the star. Finally, we include the torque due to gravitational wave emission and calculate its contribution to the torque equilibrium. Our results suggest that all three processes are significant at the cut-off frequency, and that all of them must be considered in addressing the absence of submillisecond pulsars.

Orijinal dilİngilizce
Sayfa (başlangıç-bitiş)4899-4906
Sayfa sayısı8
DergiMonthly Notices of the Royal Astronomical Society
Hacim524
Basın numarası4
DOI'lar
Yayın durumuYayınlandı - 1 Eki 2023

Bibliyografik not

Publisher Copyright:
© 2023 The Author(s). Published by Oxford University Press on behalf of Royal Astronomical Society.

Finansman

We thank Luciano Rezzolla, Erbil Gügercinoğlu, M. Ali Alpar and Ünal Ertan for their useful comments. KYE acknowledges support from the Scientific and Technological Research Council of Turkey (TÜBİTAK) through project number 112T105. We thank the anonymous referee for constructive comments, which helped us to improve the manuscript.

FinansörlerFinansör numarası
Türkiye Bilimsel ve Teknolojik Araştırma Kurumu112T105

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