Evolution of the bursting-layer wave during a Type 1 X-ray burst

TL;DR

This study investigates the evolution of waves during Type 1 X-ray bursts, finding that coupling between surface and crustal waves is weak, which challenges previous models explaining QPO frequency drifts.

Contribution

The paper provides a detailed analysis showing that the coupling between bursting layer waves and crustal interface waves is weak, contradicting earlier hypotheses about QPO cut-offs.

Findings

Weak coupling between surface and crustal waves during bursts

Crustal-interface wave does not significantly influence burst dynamics

No early QPO cut-off occurs due to wave coupling

Abstract

In a popular scenario due to Heyl, quasi periodic oscillations (QPOs) which are seen during type 1 X-ray bursts are produced by giant travelling waves in neutron-star oceans. Piro and Bildsten have proposed that during the burst cooling the wave in the bursting layer may convert into a deep crustal interface wave, which would cut off the visible QPOs. This cut-off would help explain the magnitude of the QPO frequency drift, which is otherwise overpredicted by a factor of several in Heyl's scenario. In this paper, we study the coupling between the bursting layer and the deep ocean. The coupling turns out to be weak and only a small fraction of the surface-wave energy gets transferred to that of the crustal-interface wave during the burst. Thus the crustal-interface wave plays no dynamical role during the burst, and no early QPO cut-off should occur.