2004ApJ...600..939H

During a type I burst, the turbulent deflagration front may excite waves in the neutron star ocean and upper atmosphere with frequencies ω∼1 Hz. These waves may be observed as highly coherent flux oscillations during the burst. The frequencies of these waves change as the upper layers of the neutron star cool, which accounts for the small variation in the observed quasi-periodic oscillation (QPO) frequencies. In principle, several modes could be excited, but the fundamental buoyant r-mode exhibits significantly larger variability for a given excitation than all of the other modes. An analysis of modes in the burning layers themselves and the underlying ocean shows that it is unlikely these modes can account for the observed burst oscillations. On the other hand, photospheric modes that reside in a cooler portion of the neutron star atmosphere may provide an excellent explanation for the observed oscillations.