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Astron. Astrophys. 345, 117-120 (1999)
4. Summary
New values for the spin period of SMC X-1 have been determined
during recent ROSAT observations. These observations clearly
show that the steady spin-up of the neutron star has continued. This
makes SMC X-1 the exceptional X-ray pulsar in which no spin-down
episode has been observed, though it is still unknown whether this
spin-up occurs in reality or it is just an apparent superposition of
more frequent spin-up and spin-down episodes. The magnetic moment of
the pulsar could be as small as ![[FORMULA]](img59.gif)
if
its spin trend can be described by classical accretion torque models.
Detailed timing observations are strongly recommended to resolve this
subject, and will have important implications on the theoretical
models for angular momentum transfer between a magnetic neutron star
and the surrounding accretion disk.
© European Southern Observatory (ESO) 1999
Online publication: April 12, 1999
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