Anti-correlation between X-ray luminosity and pulsed fraction in the Small Magellanic Cloud pulsar SXP 1323

11 Sep 2018, 09:50


Jun Yang (University of Utah)


We report the evidence for the anti-correlation between pulsed fraction (PF) and luminosity of the X-ray pulsar SXP 1323, found for the first time in a luminosity range $10^{35}$--$10^{37}$ erg s$^{-1}$ from observations spanning 15 years. The phenomenon of a decrease in X-ray PF when the source flux increases has been observed in our pipeline analysis of other X-ray pulsars in the Small Magellanic Cloud (SMC). It is expected that the luminosity under a certain value decreases as the PF decreases due to the propeller effect. Above the propeller region, an anti-correlation between the PF and flux might occur either as a result of an increase in the un-pulsed component of the total emission or a decrease of the pulsed component. Additional modes of accretion may also be possible, such as spherical accretion and a change in emission geometry. At higher mass accretion rates, the accretion disk could also extend closer to the neutron star (NS) surface, where a reduced inner radius leads to hotter inner disk emission. These modes of plasma accretion may affect the change in the beam configuration to fan-beam dominant emission.

Primary author

Jun Yang (University of Utah)


Daniel Wik (University of Utah) Andreas Zezas (Harvard-Smithsonian Center for Astrophysics) Malcolm Coe (University of Southampton) Jeremy Drake (Harvard-Smithsonian Center for Astrophysics) JaeSub Hong (Harvard-Smithsonian Center for Astrophysics) Silas Laycock (University of Massachusetts, Lowell)

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