Statistics – Computation
Scientific paper
Jan 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009aas...21341003r&link_type=abstract
American Astronomical Society, AAS Meeting #213, #410.03; Bulletin of the American Astronomical Society, Vol. 41, p.211
Statistics
Computation
Scientific paper
X-ray binary systems where the X-ray source is a pulsar can be ideal systems for a dynamical determination of the neutron star's mass. The orbital period, the semiamplitude of the optical star's radial velocity curve, the duration of the X-ray eclipse, and the projected semimajor axis of the pulsar's orbit (measured from the pulse arrival times) can be combined to yield the masses of both stars. We consider six systems where the needed measurements have been made: Vela X-1, 4U 1538-52, SMC X-1, LMC X-4, Cen X-3, and Her X-1. In previous studies, two approximations have been used to determine the neutron star's mass. One involves the computation of the effective Roche lobe radius, and one involves the computation of the X-ray eclipse duration. We use an "exact" numerical code based on Roche geometry and a genetic optimizer to analyze the published data for these systems. We find preliminary masses for the neutron stars of 1.78 ± 0.25 M(odot) for Vela X-1, 0.85 ± 0.13 M(odot) for 4U 1538-52, 0.88 ± 0.12 M(odot) for SMC X-1, 1.02 ± 0.07 M(odot) for LMC X-4, 1.34 ± 0.20 M(odot)for Cen X-3, and 1.13 ± 0.36 M(odot) for Her X-1. The masses for Vela X-1 and Cen X-3 agree with the previously published results, whereas the masses for the four remaining systems are roughly 1σ lower than the previous results. We discuss the limits of the approximations that were used to derive the earlier mass determinations. We also comment on the implications our new mass measurements have for observationally refining the upper and lower bounds of the neutron star mass distribution.
Orosz Jerome A.
Rawls Meredith L.
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