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Researchers find the first neutron star that bursts as predicted.

For the first time, researchers at MIT and elsewhere have detected all phases of thermonuclear burning in a neutron star. The star, located close to the center of the galaxy in the globular cluster Terzan 5, is a "model burster," says Manuel Linares, a postdoc at MIT's Kavli Institute for Astrophysics and Space Research.
Linares and his colleagues from MIT, McGill University, the University of Minnesota and the University of Amsterdam analysed X-ray observations from NASA's Rossi X-ray Timing Explorer (RXTE) satellite, and discovered the star is the first of its kind to burst the way that models predict. What's more, the discovery may help explain why such a model star has not been detected until now. A paper to be published in the March 20 issue of The Astrophysical Journal details the group's findings.

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Title: Implications of burst oscillations from the slowly rotating accreting pulsar IGR 17480-2446 in the globular cluster Terzan 5
Authors: Y. Cavecchi, A. Patruno, B. Haskell, A.L. Watts, Y. Levin, M. Linares, D. Altamirano, R. Wijnands, M. van der Klis
(Version v2)

The recently-discovered accreting X-ray pulsar IGR J17480--2446 spins at a frequency of ~11 Hz. We show that Type I X-ray bursts from this source display oscillations at the same frequency as the stellar spin. IGR J17480--2446 is the first secure case of a slowly rotating neutron star which shows Type I burst oscillations, all other sources featuring such oscillations spin at hundreds of Hertz. This means that we can test burst oscillation models in a completely different regime. We explore the origin of Type I burst oscillations in IGR J17480--2446 and conclude that they are not caused by global modes in the neutron star ocean. We also show that the Coriolis force is not able to confine an oscillation-producing hot-spot on the stellar surface. The most likely scenario is that the burst oscillations are produced by a hot-spot confined by hydromagnetic stresses.

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Title: The spin and orbit of the newly discovered pulsar IGR J17480-2446
Authors: A. Papitto (Univ.Cagliari), A.D'Ai' (Univ.Palermo), S.Motta (INAF-OAB), A.Riggio (INAF-OAC), L.Burderi (Univ.Cagliari), T.Di Salvo (Univ.Palermo), T.Belloni (INAF-OAB)

We present an analysis of the spin and orbital properties of the newly discovered accreting pulsar IGR J17480-2446, located in the globular cluster Terzan 5. Considering the pulses detected by the Rossi X-ray Timing Explorer at a period of 90.539646(6) ms, we derive a solution for the 21.2750(5) hr binary system. The binary mass function is estimated as 0.021259(5) Msun, indicating a main sequence companion star with a mass in the range 0.4--1.0 Msun.
We also report on the detection of pulsations at the spin period of the source during a Swift observation performed ~2 d before the beginning of the RXTE coverage. Assuming that the inner disc radius lies in between the neutron star radius and the corotation radius while the source shows pulsations, we estimate the magnetic field of the neutron star to be within ~2E8 G and ~2.4E10 G. Together with the value of the neutron star spin period, such an estimate puts this source in the still poorly sampled population of slow, possibly mildly recycled, accreting pulsars.

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