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arXiv · 1506.03600

On the maximum accretion luminosity of magnetized neutron stars: connecting X-ray pulsars and ultraluminous X-ray sources

Alexander A. Mushtukov·Valery F. Suleimanov·Sergey S. Tsygankov·Juri Poutanen
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Abstract

We study properties of luminous X-ray pulsars using a simplified model of the accretion column. The maximal possible luminosity is calculated as a function of the neutron star (NS) magnetic field and spin period. It is shown that the luminosity can reach values of the order of $10^{40}\,{\rm erg/s}$ for the magnetar-like magnetic field ($B\gtrsim 10^{14}\,{\rm G}$) and long spin periods ($P\gtrsim 1.5\,{\rm s}$). The relative narrowness of an area of feasible NS parameters which are able to provide higher luminosities leads to the conclusion that $L\simeq 10^{40}\,\,{\rm erg/s}$ is a good estimate for the limiting accretion luminosity of a NS. Because this luminosity coincides with the cut-off observed in the high mass X-ray binaries luminosity function which otherwise does not show any features at lower luminosities, we can conclude that a substantial part of ultra-luminous X-ray sources are accreting neutron stars in binary systems.

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Alexander A. Mushtukov, Valery F. Suleimanov, Sergey S. Tsygankov, Juri Poutanen. 2015-06-11. On the maximum accretion luminosity of magnetized neutron stars: connecting X-ray pulsars and ultraluminous X-ray sources. https://doi.org/10.1093/mnras%2Fstv2087

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