On the Curious Pulsation Properties of the Accreting Millisecond Pulsar IGR J17379-3747

Peter Bult, Craig B. Markwardt, Diego Altamirano, Zaven Arzoumanian, Deepto Chakrabarty, Keith C. Gendreau, Sebastien Guillot, Gaurava K. Jaisawal, Paul S. Ray, Tod E. Strohmayer

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Abstract

We report on the Neutron Star Interior Composition Explorer (NICER) monitoring campaign of the 468 Hz accreting millisecond X-ray pulsar IGR J17379-3747. From a detailed spectral and timing analysis of the coherent pulsations we find that they show a strong energy dependence, with soft thermal emission lagging about 640 µs behind the hard, Comptonized emission. Additionally, we observe uncommonly large pulse fractions, with measured amplitudes in excess of 20% sinusoidal fractional amplitude across the NICER passband and fluctuations of up to similar to 70%. Based on a phase-resolved spectral analysis, we suggest that these extreme properties might be explained if the source has an unusually favorable viewing geometry with a large magnetic misalignment angle. Due to these large pulse fractions, we were able to detect pulsations down to quiescent luminosities (similar to 5 x 1033 erg s-1. We discuss these low-luminosity pulsations in the context of transitional millisecond pulsars.
Original languageEnglish
Article number70
JournalAstrophysical Journal
Volume877
Issue number2
Number of pages12
ISSN0004-637X
DOIs
Publication statusPublished - 2019

Keywords

  • Stars: neutron
  • X-rays: binaries
  • X-rays: individual (IGR J17379-3747)

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