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

Abstract

The Neutron Star Interior Composition Explorer (NICER) has observed seven thermonuclear X-ray bursts from the Low Mass X-ray Binary (LMXB) neutron star 4U 1728-34 from the start of the mission's operations until February of 2019. 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 rms amplitudes of $48\pm 9\%$ and $46\pm 9\%$, 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 $7.7\pm 1.5\%$ rms in the 0.3 to 6.2 keV energy band. We discuss the implications of these large-amplitude burst oscillations, finding they are difficult to explain with the current theoretical models for X-ray burst tail oscillations.

arXiv comment14 pages, 6 figures, published in ApJ 878, 2, 145

References in corpus (21)

• Thermonuclear (type-I) X-ray bursts observed by the Rossi X-ray Timing Explorer
• Nuclear-Powered Millisecond Pulsars and the Maximum Spin Frequency of Neutron Stars
• Thermonuclear burst oscillations
• Propagation of thermonuclear flames on rapidly rotating neutron stars: extreme weather during type I X-ray bursts
• Discovery of coherent millisecond X-ray pulsations in Aql X-1
• Rotational Evolution During Type I X-Ray Bursts
• Intermittent millisecond X-ray pulsations from the neutron-star X-ray transient SAX J1748.9-2021 in the globular cluster NGC 6440
• On the Amplitude of Burst Oscillations in 4U 1636-54: Evidence for Nuclear Powered Pulsars
• R-Modes on Rapidly Rotating, Relativistic Stars: I. Do Type-I Bursts Excite Modes in the Neutron-Star Ocean?
• The Frequency Stability of Millisecond Oscillations in Thermonuclear X-Ray Bursts
• Intermittent pulsations in an accretion-powered millisecond pulsar
• On the radiation beaming of bright X-ray pulsars and constraints on neutron star mass-radius relation
• An Atlas of Burst Oscillations and Spectral Properties in 4U 1728-34
• Phase-coherent timing of the accreting millisecond pulsar SAX J1748.9-2021
• Why is it Difficult to Detect a Millisecond Pulsar in Neutron Star X-ray Binaries?
• Analysis of variability in the burst oscillations of the accreting millisecond pulsar XTE J1814-338
• Modeling the X-rays from the Central Compact Object PSR J1852+0040 in Kesteven 79: Evidence for a Strongly Magnetized Neutron Star
• X-ray Burst Oscillations: From Flame Spreading to the Cooling Wake
• The Effect of the Mass Accretion Rate on the Burst Oscillations in 4U 1728-34
• Evolution of the bursting-layer wave during a Type 1 X-ray burst
• Generation of Type I X-ray Burst Oscillations by Unstable Surface Modes

Cited by in corpus (7)

• The X-ray bursts of XTE J1739-285: a NICER sample
• Thermonuclear X-ray bursts from LMXB 4U 1636$-$536 observed with AstroSat
• Nuclear-powered X-ray millisecond pulsars
• Discovery of a 584.65 Hz Burst Oscillation in the Low Mass X-Ray Binary 4U 1730--22
• GECAM detection of a bright type-I X-ray burst from 4U 0614+09: confirmation its spin frequency at 413 Hz
• AstroSat and NuSTAR observations of XTE J1739-285 during the 2019-2020 outburst
• A transition from mixed-fuel to pure-helium thermonuclear bursts in Terzan 5 X-3/Swift J174805.3-244637