A. Patruno, M. A. Alpar, M. van der Klis, E. P. J. van den Heuvel E. P. J.
The low mass X-ray binary IGR J17480-2446 in the globular cluster Terzan 5
harbors an 11 Hz accreting pulsar. This is the first object discovered in a
globular cluster with a pulsar spinning at such low rate. The accreting pulsar
is anomalous because its characteristics are very different from the other five
known slow accreting pulsars in galactic low mass X-ray binaries. Many features
of the 11 Hz pulsar are instead very similar to those of accreting millisecond
pulsars, spinning at frequencies >100 Hz. Understanding this anomaly is very
valuable because IGR J17480-2446 can be the only accreting pulsar discovered so
far which is in the process of becoming an accreting millisecond pulsar. We
first verify that the neutron star in IGR J17480-2446 is indeed spinning up by
carefully analysing X-ray data with coherent timing techniques that account for
the presence of timing noise. We then study the present Roche Lobe Overflow
epoch and the two previous spin-down epochs dominated by magneto dipole
radiation and stellar wind accretion. We find that IGR J17480-2446 is very
likely a mildly recycled pulsar and suggest that it has started a spin-up phase
in an exceptionally recent time, that has lasted less than a few 10^7 yr. We
also find that the total age of the binary is surprisingly low (<10^8 yr) when
considering typical parameters for the newborn neutron star and propose
different scenarios to explain this anomaly.
View original:
http://arxiv.org/abs/1112.5315
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