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arXiv · 1712.05322

Peculiarities of super-Eddington flares from the X-ray pulsar LMC X-4 with NuSTAR

A. E. Shtykovsky·V. A. Arefiev·A. A. Lutovinov·S. V. Molkov
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Abstract

We present results of the analysis of super-Eddington flares registered from the X-ray pulsar LMC X-4 by the NuSTAR observatory in the broad energy range 3-79 keV. The pulsar spectrum is well described by the thermal comptonization model both in a quiescent state and during flares, when the peak luminosity reaches values $L_{\rm x} \sim (2-4)\times10^{39}$ erg s$^{-1}$. An important feature, found for the first time, is that the order of magnitude increase in the luminosity during flares is observed primarily at energies below 25-30 keV, whereas at higher energies (30-70 keV) the shape of the spectrum and the source flux remain practically unchanged. The luminosity increase is accompanied by changes in the source pulse profile -- in the energy range of 3-40 keV it becomes approximately triangular, and the pulsed fraction increases with increasing energy, reaching 60-70% in the energy range of 25-40 keV. The paper discusses possible changes in the geometry of the accretion column, which can explain variations in spectra and pulse profiles.

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A. E. Shtykovsky, V. A. Arefiev, A. A. Lutovinov, S. V. Molkov. 2017-12-14. Peculiarities of super-Eddington flares from the X-ray pulsar LMC X-4 with NuSTAR. https://doi.org/10.1134/s1063773718030015

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