The r-mode instability what we (think) we know 5+.)%6,'3,*7%89:9 - - PowerPoint PPT Presentation

The r-mode instability

what we (think) we know…

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Young radio pulsars: Original r-mode window consistent with the inferred birth spin of the Crab PSR (19 ms), but not with the 16 ms X-ray PSR J0537-6910. Recycled pulsars: Need to allow the formation of a cold 716 Hz PSR (presumably after recycling). This constrains the instability window at low temperatures. LMXBs: Nuclear burning of accreted material provides a thermostat that sets the core temperature to 108 K. Fastest systems (around 640 Hz) require smaller instability region.

“constraints”

shear bulk Consider temperature limits for systems in quiescence (Brown+Ushomirsky). If a system is r-mode unstable, how would we know? Are there systems that behave (in some sense) “funny”?

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Demonstrates that our understanding of the r-modes is incomplete. Given the “best estimate” for the main damping mechanisms, many observed LMXBs should be unstable.

r-mode puzzle

rigid crust no crust with “slippage” Rigid crust with viscous (Ekman) boundary layer would lead to sufficient damping… …but the crust is more like jelly, so the effect is reduced (“slippage”). Magnetic field is too weak to alter the nature of the boundary layer. Superfluid “mutual friction” (due to electrons scattered off vortices) has no effect. Saturation amplitude due to mode-coupling is too large to allow evolution far into instability region.

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