A Chandra X-ray study of millisecond pulsars in the globular cluster Omega Centauri: a correlation between spider pulsar companion mass and X-ray luminosity

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Title: A Chandra X-ray study of millisecond pulsars in the globular cluster Omega Centauri: a correlation between spider pulsar companion mass and X-ray luminosity
Authors: Zhao, Jiaqi, Heinke, Craig O.
Publication Year: 2023
Collection: Astrophysics
Subject Terms: Astrophysics - High Energy Astrophysical Phenomena
More Details: Millisecond pulsars (MSPs) are faint X-ray sources commonly observed in Galactic globular clusters (GCs). In this work, we investigate 18 MSPs newly found in the GC Omega Centauri ($\omega$ Cen) and search for their X-ray counterparts using Chandra observations with a total exposure time of 290.9 ks. We identify confident X-ray counterparts for 11 of the MSPs, with 9 of them newly identified in this work based on their positions, spectral properties, and X-ray colours. The X-ray spectra of 9 MSPs are well described by a neutron star hydrogen atmosphere model, while 2 MSPs are well fitted by a power-law model. The identified MSPs have X-ray luminosities ranging from $1.0\times10^{30}$ erg s$^{-1}$ to $1.4\times10^{31}$ erg s$^{-1}$. Additionally, for population comparison purposes, we study the X-ray counterpart to MSP E in the GC M71, and find its X-ray spectrum is well described by blackbody-like models with a luminosity of $1.9\times10^{30}$ erg s$^{-1}$. We investigate the empirical correlations between X-ray luminosities and minimum companion masses, as well as mass functions, of spider pulsars. Clear correlations are observed, with best-fit functions of $\log_{10}{L_X} = (1.0\pm0.1) \log_{10}{M_{c, min}} + (32.5\pm0.2)$ and $\log_{10}{L_X} = (0.35\pm0.04) \log_{10}{\rm MF} + (32.71\pm0.20)$, respectively, with an intrinsic scatter of $\log_{10}{L_X}$ of $\sim$0.3, where $L_X$ is the 0.5$-$10 keV X-ray luminosity, $M_{c, min}$ is the minimum companion mass, and MF represents the mass function, in solar masses.
Comment: 18 pages, 8 figures, 8 tables; accepted for publication in MNRAS
Document Type: Working Paper
Access URL: http://arxiv.org/abs/2309.13189
Accession Number: edsarx.2309.13189
Database: arXiv
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  Data: A Chandra X-ray study of millisecond pulsars in the globular cluster Omega Centauri: a correlation between spider pulsar companion mass and X-ray luminosity
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  Data: <searchLink fieldCode="AR" term="%22Zhao%2C+Jiaqi%22">Zhao, Jiaqi</searchLink><br /><searchLink fieldCode="AR" term="%22Heinke%2C+Craig+O%2E%22">Heinke, Craig O.</searchLink>
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  Data: 2023
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  Data: Millisecond pulsars (MSPs) are faint X-ray sources commonly observed in Galactic globular clusters (GCs). In this work, we investigate 18 MSPs newly found in the GC Omega Centauri ($\omega$ Cen) and search for their X-ray counterparts using Chandra observations with a total exposure time of 290.9 ks. We identify confident X-ray counterparts for 11 of the MSPs, with 9 of them newly identified in this work based on their positions, spectral properties, and X-ray colours. The X-ray spectra of 9 MSPs are well described by a neutron star hydrogen atmosphere model, while 2 MSPs are well fitted by a power-law model. The identified MSPs have X-ray luminosities ranging from $1.0\times10^{30}$ erg s$^{-1}$ to $1.4\times10^{31}$ erg s$^{-1}$. Additionally, for population comparison purposes, we study the X-ray counterpart to MSP E in the GC M71, and find its X-ray spectrum is well described by blackbody-like models with a luminosity of $1.9\times10^{30}$ erg s$^{-1}$. We investigate the empirical correlations between X-ray luminosities and minimum companion masses, as well as mass functions, of spider pulsars. Clear correlations are observed, with best-fit functions of $\log_{10}{L_X} = (1.0\pm0.1) \log_{10}{M_{c, min}} + (32.5\pm0.2)$ and $\log_{10}{L_X} = (0.35\pm0.04) \log_{10}{\rm MF} + (32.71\pm0.20)$, respectively, with an intrinsic scatter of $\log_{10}{L_X}$ of $\sim$0.3, where $L_X$ is the 0.5$-$10 keV X-ray luminosity, $M_{c, min}$ is the minimum companion mass, and MF represents the mass function, in solar masses.<br />Comment: 18 pages, 8 figures, 8 tables; accepted for publication in MNRAS
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      – SubjectFull: Astrophysics - High Energy Astrophysical Phenomena
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      – TitleFull: A Chandra X-ray study of millisecond pulsars in the globular cluster Omega Centauri: a correlation between spider pulsar companion mass and X-ray luminosity
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            NameFull: Zhao, Jiaqi
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            NameFull: Heinke, Craig O.
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