Astronomy and Astrophysics – Astrophysics
Scientific paper
2007-10-16
AIPConf.Proc.983:548-550,2008
Astronomy and Astrophysics
Astrophysics
3 pages, 3 figures. To appear in the proceedings of "Forty Years of Pulsars: Millisecond Pulsars, Magnetars and More" held in
Scientific paper
10.1063/1.2900296
During accretion, a neutron star (NS) is spun up as angular momentum is transported through its liquid surface layers. We study the resulting differentially rotating profile, focusing on the impact this has for type I X-ray bursts. The viscous heating is found to be negligible, but turbulent mixing can be activated. Mixing has the greatest impact when the buoyancy at the compositional discontinuity between accreted matter and ashes is overcome. This occurs preferentially at high accretion rates or low spin frequencies and may depend on the ash composition from the previous burst. We then find two new regimes of burning. The first is ignition in a layer containing a mixture of heavier elements with recurrence times as short as ~5-30 minutes, similar to short recurrence time bursts. When mixing is sufficiently strong, a second regime is found where accreted helium mixes deep enough to burn stably, quenching X-ray bursts altogether. The carbon-rich material produced by stable helium burning would be important for triggering and fueling superbursts.
Bildsten Lars
Piro Anthony L.
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