The tremendous progress in neutron star mass measurements can be illustrated by a short description of new results obtained from November 2005 (when this book was mainly completed) to August 2006 (when last minute changes were introduced).
Jacoby et al. (2006) reported the direct measurement of the orbital decay Pb = (—3.95±0.13)x10"12 in thedouble neutron star binary PSRB2127+11C discussed in § 9.1.2 c. New timing data allowed the authors to infer more accurate values of neutron star masses, M1 (1a) = (1.358 ± 0.010) M© and M2(1) = (1.354 ± 0.010) M© (compare with the values in Table 9.4).
Bassa etal. (2006) andCocozza etal. (2006) presented new observations of a compact binary containing the millisecond pulsar J1911-5958A and a white dwarf. The pulsar was discovered in 1999 (D'Amico et al., 2001b). The pulsar timing showed that the orbit is nearly circular and the orbital period is Pb = 0. 84 days. The authors present new optical observations of the white dwarf which allowed them to measure its radial velocities. Moreover, comparing the data with white dwarf atmosphere models and theoretical mass-radius relations, Bassa etal. (2006) obtained the white dwarf mass M2 (1a) = (0.18±0.02) M©. The radial velocities and M2 gave them two equations to determine the pulsar mass M1(1a) = 1.40+016 M0. No relativistic effects have been detected from this binary.
Lorimer et al. (2006) reported the discovery of PSR J1906+0746, a young pulsar in a highly relativistic orbit with a neutron star or a white dwarf (Pb = 3.98 hr, e = 0.085). Huge periastron advance has been measured, uo & 7.°57 yr-1, which gives the total binary mass M(1a) = (2.61 ± 0.02) M0 and the binary merging time ideath ~ 300 Myr. Further observations are required to resolve M1 and M2.
Finally, Freire et al. (2006) discovered a new millisecond pulsar J1741+1351 in a circular orbit with a white dwarf (Pb = 16 days). The pulsar timing shows the Shapiro effect which gives two parameters (sin i & 0.96, M2(1a) = (0.30 ± 0.07) M0) and two respective equations to determine the pulsar mass, M1(1a) = (1.8 ± 0.3) M0, interesting for the EOS problem.
With this spectacular progress, new exciting and decisive neutron star mass measurements can be expected any day!
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