Long-term Evolution of Sco X-1: Implications for the Current Spin Frequency and Ellipticity of the Neutron Star
Sco X-1 is the brightest observed extrasolar X-ray source, which is a neutron star (NS) low-mass X-ray binary (LMXB) and is thought to have a strong potential for continuous gravitational waves (CW) detection due to its high accretion rate and relative proximity. Here, we compute the long-term evolu...
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IOP Publishing
2025-01-01
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| Online Access: | https://doi.org/10.3847/1538-4357/adabbf |
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| author | Abhijnan Kar Pulkit Ojha Sudip Bhattacharyya |
| author_facet | Abhijnan Kar Pulkit Ojha Sudip Bhattacharyya |
| author_sort | Abhijnan Kar |
| collection | DOAJ |
| description | Sco X-1 is the brightest observed extrasolar X-ray source, which is a neutron star (NS) low-mass X-ray binary (LMXB) and is thought to have a strong potential for continuous gravitational waves (CW) detection due to its high accretion rate and relative proximity. Here, we compute the long-term evolution of its parameters, particularly the NS spin frequency ( ν ) and the surface magnetic field ( B ), to probe its nature and its potential for CW detection. We find that Sco X-1 is an unusually young (∼7 × 10 ^6 yr) LMXB and constrain the current NS mass to ∼1.4–1.6 M _⊙ . Our computations reveal a rapid B decay, with the maximum current value of ∼1.8 × 10 ^8 G, which can be useful to constrain the decay models. Note that the maximum current ν value is ∼550 Hz, implying that, unlike what is generally believed, a CW emission is not required to explain the current source properties. However, ν will exceed an observed cutoff frequency of ∼730 Hz, and perhaps even the NS breakup frequency, in the future without a CW emission. The minimum NS mass quadrupole moment ( Q ) to avoid this is ∼(2–3) × 10 ^37 g cm ^2 , corresponding to a CW strain of ∼10 ^−26 . Our estimation of current ν values can improve the CW search sensitivity. |
| format | Article |
| id | doaj-art-8228d510720a45458f8a2ad9561b74e0 |
| institution | Kabale University |
| issn | 1538-4357 |
| language | English |
| publishDate | 2025-01-01 |
| publisher | IOP Publishing |
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| series | The Astrophysical Journal |
| spelling | doaj-art-8228d510720a45458f8a2ad9561b74e02025-02-04T08:00:35ZengIOP PublishingThe Astrophysical Journal1538-43572025-01-0198015110.3847/1538-4357/adabbfLong-term Evolution of Sco X-1: Implications for the Current Spin Frequency and Ellipticity of the Neutron StarAbhijnan Kar0https://orcid.org/0000-0001-9207-7803Pulkit Ojha1Sudip Bhattacharyya2https://orcid.org/0000-0002-6351-5808Department of Physical Sciences, Indian Institute of Science Education and Research Berhampur , Vigyanpuri, Ganjam 760003, India ; karabhijnan123@gmail.comCenter for Theoretical Physics , Aleja Lotnikow 32/46, 02-668, Warszawa, Poland ; pojha@cft.edu.plDepartment of Astronomy and Astrophysics, Tata Institute of Fundamental Research , 1 Homi Bhabha Road, Colaba, Mumbai 400005, India ; sudip@tifr.res.inSco X-1 is the brightest observed extrasolar X-ray source, which is a neutron star (NS) low-mass X-ray binary (LMXB) and is thought to have a strong potential for continuous gravitational waves (CW) detection due to its high accretion rate and relative proximity. Here, we compute the long-term evolution of its parameters, particularly the NS spin frequency ( ν ) and the surface magnetic field ( B ), to probe its nature and its potential for CW detection. We find that Sco X-1 is an unusually young (∼7 × 10 ^6 yr) LMXB and constrain the current NS mass to ∼1.4–1.6 M _⊙ . Our computations reveal a rapid B decay, with the maximum current value of ∼1.8 × 10 ^8 G, which can be useful to constrain the decay models. Note that the maximum current ν value is ∼550 Hz, implying that, unlike what is generally believed, a CW emission is not required to explain the current source properties. However, ν will exceed an observed cutoff frequency of ∼730 Hz, and perhaps even the NS breakup frequency, in the future without a CW emission. The minimum NS mass quadrupole moment ( Q ) to avoid this is ∼(2–3) × 10 ^37 g cm ^2 , corresponding to a CW strain of ∼10 ^−26 . Our estimation of current ν values can improve the CW search sensitivity.https://doi.org/10.3847/1538-4357/adabbfGravitational wavesNeutron starsLow-mass x-ray binary starsAccretionX-ray binary stars |
| spellingShingle | Abhijnan Kar Pulkit Ojha Sudip Bhattacharyya Long-term Evolution of Sco X-1: Implications for the Current Spin Frequency and Ellipticity of the Neutron Star The Astrophysical Journal Gravitational waves Neutron stars Low-mass x-ray binary stars Accretion X-ray binary stars |
| title | Long-term Evolution of Sco X-1: Implications for the Current Spin Frequency and Ellipticity of the Neutron Star |
| title_full | Long-term Evolution of Sco X-1: Implications for the Current Spin Frequency and Ellipticity of the Neutron Star |
| title_fullStr | Long-term Evolution of Sco X-1: Implications for the Current Spin Frequency and Ellipticity of the Neutron Star |
| title_full_unstemmed | Long-term Evolution of Sco X-1: Implications for the Current Spin Frequency and Ellipticity of the Neutron Star |
| title_short | Long-term Evolution of Sco X-1: Implications for the Current Spin Frequency and Ellipticity of the Neutron Star |
| title_sort | long term evolution of sco x 1 implications for the current spin frequency and ellipticity of the neutron star |
| topic | Gravitational waves Neutron stars Low-mass x-ray binary stars Accretion X-ray binary stars |
| url | https://doi.org/10.3847/1538-4357/adabbf |
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