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arXiv · 1009.5427

Evidence for a Massive Neutron Star from a Radial-Velocity Study of the Companion to the Black Widow Pulsar PSR B1957+20

M. H. van Kerkwijk·R. Breton·S. R. Kulkarni
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Abstract

The most massive neutron stars constrain the behavior of ultra-dense matter, with larger masses possible only for increasingly stiff equations of state. Here, we present evidence that the black widow pulsar, PSR B1957+20, has a high mass. We took spectra of its strongly irradiated companion and found an observed radial-velocity amplitude of K_obs=324+/-3 km/s. Correcting this for the fact that, due to the irradiation, the center of light lies inward relative to the center of mass, we infer a true radial-velocity amplitude of K_2=353+/-4 km/s and a mass ratio q=M_PSR/M_2=69.2+/-0.8. Combined with the inclination i=65+/-2 deg inferred from models of the lightcurve, our best-fit pulsar mass is M_PSR=2.40+/-0.12 M_sun. We discuss possible systematic uncertainties, in particular in the lightcurve modeling. Taking an upper limit of i<85 deg based on the absence of radio eclipses at high frequency, combined with a conservative lower-limit to the motion of the center of mass, K_2>343 km/s (q>67.3), we infer a lower limit to the pulsar mass of M_PSR>1.66 M_sun.

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M. H. van Kerkwijk, R. Breton, S. R. Kulkarni. 2010-12-14. Evidence for a Massive Neutron Star from a Radial-Velocity Study of the Companion to the Black Widow Pulsar PSR B1957+20. https://doi.org/10.1088/0004-637x%2F728%2F2%2F95

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