The origin of the bimodal luminosity distribution of ultraluminous X-ray pulsars

Abstract

The mechanism that can be responsible for the bimodal luminosity distribution of super-Eddington X-ray pulsars in binary systems is pointed out. The transition from the high to low state of these objects is explained by accretion flow spherization due to the radiation pressure at certain (high) accretion rates. The transition between the states can be associated with a gradual change in the accretion rate. The complex behavior of the recently discovered ultraluminous X-ray pulsars M 82 X-2, NGC 5907 ULX-1, and NGC 7793 P13 is explained by the proposed mechanism. The proposed model also naturally explains the measured spinup of the neutron star in these pulsars, which is slower than the expected one by several times.

15 pages, 2 figures

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• Detection of 125.5-day Optical Periodic Modulation of the Neutron Star M51 ULX-8
• Investigating the nature of the ultraluminous X-ray sources in the galaxy NGC 925
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• Populations of ultraluminous X-ray sources in galaxies: origin and evolution
• Do the periodic activities of repeating fast radio bursts represent the spins of neutron stars?