NICER Observation of Unusual Burst Oscillations in 4U 1728-34

Simin Mahmoodifar*, Tod E. Strohmayer, Peter Bult, Diego Altamirano, Zaven Arzoumanian, Deepto Chakrabarty, Keith C. Gendreau, Sebastien Guillot, Jeroen Homan, Gaurava K. Jaisawal, Laurens Keek, Michael T. Wolff

*Corresponding author for this work

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Abstract

The Neutron Star Interior Composition Explorer has observed seven thermonuclear X-ray bursts from the low-mass X-ray binary neutron star 4U 1728−34 from the start of the mission’s operations until 2019 February. Three of these bursts show oscillations in their decaying tail, with frequencies that are within 1 Hz of the previously detected burst oscillations from this source. Two of these burst oscillations have unusual properties: they have large fractional root mean square (rms) amplitudes of 48% ± 9% and 46% ± 9%, and they are detected only at photon energies above 6 keV. By contrast, the third detected burst oscillation is compatible with previous observations of this source, with a fractional rms amplitude of 7.7% ± 1.5% rms in the 0.3 to 6.2 keV energy band. We discuss the implications of these large-amplitude burst oscillations, finding that they are difficult to explain with the current theoretical models for X-ray burst tail oscillations.
Original languageEnglish
Article number145
JournalAstrophysical Journal
Volume878
Issue number2
Number of pages7
ISSN0004-637X
DOIs
Publication statusPublished - 2019

Keywords

  • Methods: data analysis
  • Stars: neutron
  • Stars: oscillations
  • X-rays: binaries
  • X-rays: individual (4U 1728,34)

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