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arXiv · 1607.03933

Luminosity dependence of the cyclotron line and evidence for the accretion regime transition in V 0332+53

Victor Doroshenko·Sergey S. Tsygankov·Alexander A. Mushtukov·Alexander A. Lutovinov·Andrea Santangelo·Valery F. Suleimanov·Juri Poutanen
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Abstract

We report on the analysis of NuSTAR observations of the Be-transient X-ray pulsar V 0332+53 during the giant outburst in 2015 and another minor outburst in 2016. We confirm the cyclotron-line energy-luminosity correlation previously reported in the source and the line energy decrease during the giant outburst. Based on 2016 observations, we find that a year later the line energy has increased again essentially reaching the pre-outburst values. We discuss this behaviour and conclude that it is likely caused by a change of the emission region geometry rather than previously suggested accretion-induced decay of the neutron stars magnetic field. At lower luminosities, we find for the first time a hint of departure from the anticorrelation of line energy with flux, which we interpret as a transition from super- to sub-critical accretion associated with the disappearance of the accretion column. Finally, we confirm and briefly discuss the orbital modulation observed in the outburst light curve of the source.

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Victor Doroshenko, Sergey S. Tsygankov, Alexander A. Mushtukov, Alexander A. Lutovinov, Andrea Santangelo, Valery F. Suleimanov, Juri Poutanen. 2017-01-31. Luminosity dependence of the cyclotron line and evidence for the accretion regime transition in V 0332+53. https://doi.org/10.1093/mnras%2Fstw3236

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