Binary Pulsar PSR 1913 + 16: Model for Its Origin

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Abstract
The existing observational data for the binary pulsar PSR 1913 + 16 are sufficient to give a rather well-defined model for the system. On the basis of evolutionary considerations, the pulsar must be a neutron star near the upper mass limit of 1.2 solar masses ( M ⊙ ). The orbital inclination is probably high, i ≳ 70°, and the mass of the unseen companion probably lies close to the upper limit of the range 0.25 M ⊙ to 1.0 M ⊙ . The secondary cannot be a main sequence star and is probably a degenerate helium dwarf. At the 5.6-kiloparsec distance indicated by the dispersion measure, the magnetic dipole model gives an age of ∼4 × 10 4 years, a rate of change of the pulsar period of P ∼2 nanoseconds per day, and a surface magnetic field strength ∼ ⅓ that of the Crab pulsar. The pulsar is fainter than an apparent magnitude V ∼+ 26.5 and is at least ∼80 times fainter than the Crab pulsar in the x-ray band. The companion star should be fainter than V ∼+ 30, and a radio supernova remnant may be detectable near the position of the pulsar at a flux level of ≲10 janskys. Important tests of this model will be provided by more accurate measurement of P and by a careful search for a faint supernova remnant.