Brice, N;
Zane, S;
Turolla, R;
Wu, K;
(2021)
Super-Eddington Emission from Accreting, Highly Magnetised Neutron Stars with a Multipolar Magnetic Field.
Monthly Notices of the Royal Astronomical Society
, 504
(1)
pp. 701-715.
10.1093/mnras/stab915.
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Abstract
Pulsating ultraluminous X-ray sources (PULXs) are characterized by an extremely large luminosity (>1040 erg s−1). While there is a general consensus that they host an accreting, magnetized neutron star (NS), the problem of how to produce luminosities >100 times the Eddington limit, LE, of a solar mass object is still debated. A promising explanation relies on the reduction of the opacities in the presence of a strong magnetic field, which allows for the local flux to be much larger than the Eddington flux. However, avoiding the onset of the propeller effect may be a serious problem. Here, we reconsider the problem of column accretion on to a highly magnetized NS, extending previously published calculations by relaxing the assumption of a pure dipolar field and allowing for more complex magnetic field topologies. We find that the maximum luminosity is determined primarily by the magnetic field strength near the NS surface. We also investigate other factors determining the accretion column geometry and the emergent luminosity, such as the assumptions on the parameters governing the accretion flow at the disc–magnetosphere boundary. We conclude that a strongly magnetized NS with a dipole component of ∼1013 G, octupole component of ∼1014 G, and spin period ∼1 s can produce a luminosity of ∼1041 erg s−1 while avoiding the propeller regime. We apply our model to two PULXs, NGC 5907 ULX-1, and NGC 7793 P13, and discuss how their luminosity and spin period rate can be explained in terms of different configurations, either with or without multipolar magnetic components.
| Type: | Article |
|---|---|
| Title: | Super-Eddington Emission from Accreting, Highly Magnetised Neutron Stars with a Multipolar Magnetic Field |
| Open access status: | An open access version is available from UCL Discovery |
| DOI: | 10.1093/mnras/stab915 |
| Publisher version: | https://doi.org/10.1093/mnras/stab915 |
| Language: | English |
| Additional information: | This version is the version of record. For information on re-use, please refer to the publisher’s terms and conditions. |
| Keywords: | Accretion, accretion discs, stars: neutron, X-rays: binaries |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Space and Climate Physics |
| URI: | https://discovery-pp.ucl.ac.uk/id/eprint/10126434 |
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