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 .