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Title: The formation of the eccentric-orbit millisecond pulsar J1903+0327 and the origin of single millisecond pulsars
Authors: Simon Portegies Zwart (Leiden Observatory), Ed van den Heuvel (UvA), Joeri van Leeuwen (ASTRON), Gijs Nelemans (Radboud University)

The millisecond pulsar J1903+0327 is accompanied by an ordinary G-dwarf star in an unusually wide (P_{orb} \simeq 95.2\,days) and eccentric (e \simeq 0.44) orbit. The standard model for producing MSPs fails to explain the orbital characteristics of this extraordinary binary, and alternative binary models are unable to explain the observables. We present a triple-star model for producing MSPs in relatively wide eccentric binaries with a normal (main-sequence) stellar companion. We start from a stable triple system consisting of a Low-Mass X-ray Binary (LMXB) with an orbital period of at least 1 day, accompanied by a G-dwarf in a wide and possibly eccentric orbit. Variations in the initial conditions naturally provide a satisfactory explanation for the unexplained triple component in the eclipsing soft X-ray transient 4U~2129+47 or the cataclysmic variable EC 19314-5915. The best explanation for J1903, however, results from the expansion of the orbit of the LMXB, driven by the mass transfer from the evolving donor star to its neutron star companion, which causes the triple eventually to becomes dynamically unstable. Using numerical computations we show that, depending on the precise system configuration at the moment the triple becomes dynamically unstable, the ejection of each of the three components is possible. If the donor star of the LMXB is ejected, a system resembling J1903, will result. If the neutron star is ejected, a single MSP results. This model therefore also provides a straightforward mechanism for forming single MSP in the Galactic disk. We conclude that the Galaxy contains some 30--300 binaries with characteristics similar to J1903, and about an order of magnitude fewer single millisecond pulsars produced with the proposed triple scenario.

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PSR J1903+0327 is a millisecond pulsar in a highly eccentric binary orbit.
The pulsar was discovered in an ongoing L-band (1.4 GHz) survey with the 305 m diameter Arecibo radio telescope.
The pulse period is 2.15 ms. Analysis of the pulse timing residuals shows a binary orbit with a period of 95.17 days, and a high eccentricity, e = 0.437. The mass of the companion is ~1 solar mass, while the pulsar mass is unusually large at ~1.74 solar masses. A possible near-infrared companion, KS = 18 (2.22), is observed in Gemini North images at its radio position.

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Astronomers baffled by weird, fast-spinning pulsar
Astronomers are baffled after finding an exotic type of star called a pulsar apparently locked in an elongated orbit around a star much like the sun -- an arrangement defying what had been known about such objects.


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A mysterious and unique star system has been discovered by Jodrell Bank astronomers.
The scientists have found the remnants of a dead 'pulsar' star spinning incredibly fast around another sun in an elongated orbit - a combination never seen before.

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Title: An Eccentric Binary Millisecond Pulsar in the Galactic Plane
Authors: D. J. Champion, S. M. Ransom, P. Lazarus, F. Camilo, C. Bassa, V. M. Kaspi, D. J. Nice, P. C. C. Freire, I. H. Stairs, J. van Leeuwen, B. W. Stappers, J. M. Cordes, J. W. T. Hessels, D. R. Lorimer, Z. Arzoumanian, D. C. Backer, N. D. R. Bhat, S. Chatterjee, I. Cognard, J. S. Deneva, C.-A. Faucher-Giguere, B. M. Gaensler, J. L. Han, F. A. Jenet, L. Kasian, V. I. Kondratiev, M. Kramer, J. Lazio, M. A. McLaughlin, A. Venkataraman, W. Vlemmings

Binary pulsar systems are superb probes of stellar and binary evolution and the physics of extreme environments. In a survey with the Arecibo telescope, we have found PSR J1903+0327, a radio pulsar with a rotational period of 2.15 ms in a highly eccentric (e = 0.44) 95-day orbit around a solar mass companion. Infrared observations identify a possible main-sequence companion star. Conventional binary stellar evolution models predict neither large orbital eccentricities nor main-sequence companions around millisecond pulsars. Alternative formation scenarios involve recycling a neutron star in a globular cluster then ejecting it into the Galactic disk or membership in a hierarchical triple system. A relativistic analysis of timing observations of the pulsar finds its mass to be 1.74 0.04 Msun, an unusually high value.

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CSIRO astronomers said they are stumped by the formation of an "eccentric" fast-spinning star.
Scientists at the Australia Telescope National Facility will today publish their findings in the online journal Science Express on the pulsar, which is called J1903+0327.
Astronomer David Champion and his colleagues have discovered the star is 20,000 light years away, and spins at 465 revolutions per second.

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