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Astron. Astrophys. 345, 117-120 (1999)

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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] 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.

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© European Southern Observatory (ESO) 1999

Online publication: April 12, 1999