Her X-1: correlated variability of the 1.24 sec and the 35
day periods
Ruediger Staubert
Susanne Schandl
Abstract
Both the 1.24 s pulsational period and the 35 day turn-on period
of Her X-1 show long-term variability. It is shown that both
periods vary in a highly correlated way: when the spin-up rate
drops the 35 day precessional period gets shorter. This
correlation is most evident on long time scales ( ~ 2000 days),
e.g. during two extended spin-down episodes, but also on shorter
timescales (a few 100 days) on which quasi-periodic variations are
apparent. The likely common cause are variations of the rate of
mass accretion onto the neutron star. A physical explanation
within the framework of the coronal wind model is proposed.
Further details on the jitter of the 35 day clock will be
discussed. Recently, a third 'extended low' has been observed
which my allow further insight into a possible correlation of such
events with spin-down episodes.
File translated from TEX by TTH, version 2.32.
On 16 Jul 1999, 09:19.