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Post Info TOPIC: PSR J0437-4715


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RE: PSR J0437-4715
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Title: Evolution of low mass close binary systems with a neutron star: its dependence with the initial neutron star mass
Authors: M. A. De Vito, O. G. Benvenuto

We construct a set of binary evolutionary sequences for systems composed by a normal, solar composition, donor star together with a neutron star. We consider a variety of masses for each star as well as for the initial orbital period corresponding to systems that evolve to ultra-compact or millisecond pulsar-helium white dwarf pairs. Specifically, we select a set of donor star masses of 0.50, 0.65, 0.80, 1.00, 1.25, 1.50, 1.75, 2.00, 2.25, 2.50, 3.00, and 3.50 solar masses, whereas for the accreting neutron star we consider initial masses values of 0.8, 1.0, 1.2, and 1.4 solar masses.
The considered initial orbital period interval ranges from 0.5 to 12 days. It is found that the evolution of systems, with fixed initial values for the orbital period and the mass of the normal donor star, heavily depends upon the mass of the neutron star. In some cases, varying the initial value of the neutron star mass, we obtain evolved configurations ranging from ultra-compact to widely separated objects.
We also analyse the dependence of the final orbital period with the mass of the white dwarf. In agreement with previous expectations, our calculations show that the final orbital period-white dwarf mass relation is fairly insensitive to the initial neutron star mass value. A new period-mass relation based on our own calculations is proposed, which is in good agreement with period-mass relations available in the literature.
As consequence of considering a set of values for the initial neutron star mass, these models allow finding different plausible initial configurations (donor and neutron star masses and orbital period interval) for some of the best observed binary systems of the kind we are interested in here. We apply our calculations to analyse the case of PSR J0437-4715.

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Title: The spectrum of the recycled PSR J0437-4715 and its white dwarf companion
Authors: M. Durant (UFlorida), O. Kargaltsev, G. G. Pavlov, P. M. Kowalski, B. Posselt, M. H. van Kerkwijk, D. L. Kaplan

We present extensive spectral and photometric observations of the recycled pulsar/white-dwarf binary containing PSR J0437-4715, which we analysed together with archival X-ray and gamma-ray data, to obtain the complete mid-infrared to gamma-ray spectrum. We first fit each part of the spectrum separately, and then the whole multi-wavelength spectrum. We find that the optical-infrared part of the spectrum is well fit by a cool white dwarf atmosphere model with pure hydrogen composition. The model atmosphere (Teff = 3950150K, log g=6.980.15, R_WD=(1.90.2)e9 cm) fits our spectral data remarkably well for the known mass and distance (M=0.250.02 solar masses, d=156.31.3pc), yielding the white dwarf age (tau=6.00.5Gyr). In the UV, we find a spectral shape consistent with thermal emission from the bulk of the neutron star surface, with surface temperature between 1.25e5 and 3.5e5K. The temperature of the thermal spectrum suggests that some heating mechanism operates throughout the life of the neutron star. The temperature distribution on the neutron star surface is non-uniform. In the X-rays, we confirm the presence of a high-energy tail which is consistent with a continuation of the cut-off power-law component (Gamma=1.560.01, Ecut=1.10.2GeV) that is seen in gamma-rays and perhaps even extends to the near-UV.

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