The formation of the eccentric-orbit millisecond pulsar J1903+0327 and the origin of single millisecond pulsars
Number of pages
Faculty of Science (FNWI)
Anton Pannekoek Institute for Astronomy (API)
The millisecond pulsar (MSP) J1903+0327 is accompanied by an ordinary G dwarf star in an unusually wide (P orb 95.2 days)
and eccentric (e 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+0327, 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 become 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+0327 will result. If the neutron star is ejected, a single MSP results. This model therefore also
provides a straightforward mechanism for forming a single MSP in the Galactic disk. We conclude that the Galaxy contains some
30-300 binaries with characteristics similar to J1903+0327 and about an order of magnitude fewer single MSPs produced with
the proposed triple scenario.
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