Measuring the Magnetic Dipole Moment and Magnetospheric Fluctuations of SXP 18.3 with a Kalman Filter
The magnetic dipole moment μ of an accretion-powered pulsar in magnetocentrifugal equilibrium cannot be inferred uniquely from time-averaged pulse period and aperiodic X-ray flux data, because the radiative efficiency η _0 of the accretion is unknown, as are the mass, radius, and distance of the sta...
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| Format: | Article |
| Language: | English |
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IOP Publishing
2024-01-01
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| Series: | The Astrophysical Journal |
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| Online Access: | https://doi.org/10.3847/1538-4357/ad2adc |
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| author | Joseph O’Leary Andrew Melatos Nicholas J. O’Neill Patrick M. Meyers Dimitris M. Christodoulou Sayantan Bhattacharya Silas G. T. Laycock |
| author_facet | Joseph O’Leary Andrew Melatos Nicholas J. O’Neill Patrick M. Meyers Dimitris M. Christodoulou Sayantan Bhattacharya Silas G. T. Laycock |
| author_sort | Joseph O’Leary |
| collection | DOAJ |
| description | The magnetic dipole moment μ of an accretion-powered pulsar in magnetocentrifugal equilibrium cannot be inferred uniquely from time-averaged pulse period and aperiodic X-ray flux data, because the radiative efficiency η _0 of the accretion is unknown, as are the mass, radius, and distance of the star. The degeneracy associated with the radiative efficiency is circumvented if fluctuations of the pulse period and aperiodic X-ray flux are tracked with a Kalman filter, whereupon μ can be measured uniquely up to the uncertainties in the mass, radius, and distance. Here, the Kalman filter analysis is demonstrated successfully in practice for the first time on Rossi X-ray Timing Explorer observations of the X-ray transient SXP 18.3 in the Small Magellanic Cloud (SMC), which is monitored regularly. The analysis yields $\mu ={8.0}_{-1.2}^{+1.3}\,\times \,{10}^{30}\,{\rm{G}}\,{\mathrm{cm}}^{3}$ and ${\eta }_{0}={0.04}_{-0.01}^{+0.02}$ , compared to $\mu ={5.0}_{-1.0}^{+1.0}\times {10}^{30}\,{\rm{G}}\,{\mathrm{cm}}^{3}$ as inferred traditionally from time-averaged data assuming η _0 = 1. The analysis also yields time-resolved estimates of two hidden state variables, the mass accretion rate and the Maxwell stress at the disk–magnetosphere boundary. The success of the demonstration confirms that the Kalman filter analysis can be applied in the future to study the magnetic moments and disk–magnetosphere physics of accretion-powered pulsar populations in the SMC and elsewhere. |
| first_indexed | 2024-04-24T11:15:52Z |
| format | Article |
| id | doaj.art-3a196656759b440c949fbdc3a0141e7b |
| institution | Directory Open Access Journal |
| issn | 1538-4357 |
| language | English |
| last_indexed | 2024-04-24T11:15:52Z |
| publishDate | 2024-01-01 |
| publisher | IOP Publishing |
| record_format | Article |
| series | The Astrophysical Journal |
| spelling | doaj.art-3a196656759b440c949fbdc3a0141e7b2024-04-11T08:01:02ZengIOP PublishingThe Astrophysical Journal1538-43572024-01-01965210210.3847/1538-4357/ad2adcMeasuring the Magnetic Dipole Moment and Magnetospheric Fluctuations of SXP 18.3 with a Kalman FilterJoseph O’Leary0https://orcid.org/0000-0002-6547-2039Andrew Melatos1https://orcid.org/0000-0003-4642-141XNicholas J. O’Neill2Patrick M. Meyers3https://orcid.org/0000-0002-2689-0190Dimitris M. Christodoulou4https://orcid.org/0000-0002-7652-2206Sayantan Bhattacharya5https://orcid.org/0000-0001-8572-8241Silas G. T. Laycock6https://orcid.org/0000-0002-8427-0766School of Physics, University of Melbourne , Parkville, VIC 3010, Australia; Australian Research Council Centre of Excellence for Gravitational Wave Discovery (OzGrav) , Parkville, VIC 3010, AustraliaSchool of Physics, University of Melbourne , Parkville, VIC 3010, Australia; Australian Research Council Centre of Excellence for Gravitational Wave Discovery (OzGrav) , Parkville, VIC 3010, AustraliaSchool of Physics, University of Melbourne , Parkville, VIC 3010, Australia; Australian Research Council Centre of Excellence for Gravitational Wave Discovery (OzGrav) , Parkville, VIC 3010, AustraliaTheoretical Astrophysics Group, California Institute of Technology , Pasadena, CA 91125, USAUniversity of Massachusetts Lowell , Kennedy College of Sciences, Lowell, MA 01854, USA; Lowell Centre for Space Science and Technology , Lowell, MA 01854, USAUniversity of Massachusetts Lowell , Kennedy College of Sciences, Lowell, MA 01854, USA; Lowell Centre for Space Science and Technology , Lowell, MA 01854, USAUniversity of Massachusetts Lowell , Kennedy College of Sciences, Lowell, MA 01854, USA; Lowell Centre for Space Science and Technology , Lowell, MA 01854, USAThe magnetic dipole moment μ of an accretion-powered pulsar in magnetocentrifugal equilibrium cannot be inferred uniquely from time-averaged pulse period and aperiodic X-ray flux data, because the radiative efficiency η _0 of the accretion is unknown, as are the mass, radius, and distance of the star. The degeneracy associated with the radiative efficiency is circumvented if fluctuations of the pulse period and aperiodic X-ray flux are tracked with a Kalman filter, whereupon μ can be measured uniquely up to the uncertainties in the mass, radius, and distance. Here, the Kalman filter analysis is demonstrated successfully in practice for the first time on Rossi X-ray Timing Explorer observations of the X-ray transient SXP 18.3 in the Small Magellanic Cloud (SMC), which is monitored regularly. The analysis yields $\mu ={8.0}_{-1.2}^{+1.3}\,\times \,{10}^{30}\,{\rm{G}}\,{\mathrm{cm}}^{3}$ and ${\eta }_{0}={0.04}_{-0.01}^{+0.02}$ , compared to $\mu ={5.0}_{-1.0}^{+1.0}\times {10}^{30}\,{\rm{G}}\,{\mathrm{cm}}^{3}$ as inferred traditionally from time-averaged data assuming η _0 = 1. The analysis also yields time-resolved estimates of two hidden state variables, the mass accretion rate and the Maxwell stress at the disk–magnetosphere boundary. The success of the demonstration confirms that the Kalman filter analysis can be applied in the future to study the magnetic moments and disk–magnetosphere physics of accretion-powered pulsar populations in the SMC and elsewhere.https://doi.org/10.3847/1538-4357/ad2adcNeutron starsAccretionMagnetic fields |
| spellingShingle | Joseph O’Leary Andrew Melatos Nicholas J. O’Neill Patrick M. Meyers Dimitris M. Christodoulou Sayantan Bhattacharya Silas G. T. Laycock Measuring the Magnetic Dipole Moment and Magnetospheric Fluctuations of SXP 18.3 with a Kalman Filter The Astrophysical Journal Neutron stars Accretion Magnetic fields |
| title | Measuring the Magnetic Dipole Moment and Magnetospheric Fluctuations of SXP 18.3 with a Kalman Filter |
| title_full | Measuring the Magnetic Dipole Moment and Magnetospheric Fluctuations of SXP 18.3 with a Kalman Filter |
| title_fullStr | Measuring the Magnetic Dipole Moment and Magnetospheric Fluctuations of SXP 18.3 with a Kalman Filter |
| title_full_unstemmed | Measuring the Magnetic Dipole Moment and Magnetospheric Fluctuations of SXP 18.3 with a Kalman Filter |
| title_short | Measuring the Magnetic Dipole Moment and Magnetospheric Fluctuations of SXP 18.3 with a Kalman Filter |
| title_sort | measuring the magnetic dipole moment and magnetospheric fluctuations of sxp 18 3 with a kalman filter |
| topic | Neutron stars Accretion Magnetic fields |
| url | https://doi.org/10.3847/1538-4357/ad2adc |
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