Asymmetric mass ratios for bright double neutron-star mergers

R. D. Ferdman (), P. C. C. Freire, B. B. P. Perera, N. Pol, F. Camilo, S. Chatterjee, J. M. Cordes, F. Crawford, J. W. T. Hessels, V. M. Kaspi, M. A. McLaughlin, E. Parent, I. H. Stairs and J. Leeuwen
Additional contact information
R. D. Ferdman: University of East Anglia
P. C. C. Freire: Max-Planck-Institut für Radioastronomie
B. B. P. Perera: Arecibo Observatory
N. Pol: West Virginia University
F. Camilo: South African Radio Astronomy Observatory
S. Chatterjee: Cornell University
J. M. Cordes: Cornell University
F. Crawford: Franklin and Marshall College
J. W. T. Hessels: University of Amsterdam
V. M. Kaspi: McGill University
M. A. McLaughlin: West Virginia University
E. Parent: McGill University
I. H. Stairs: University of British Columbia
J. Leeuwen: ASTRON, Netherlands Institute for Radio Astronomy

Nature, 2020, vol. 583, issue 7815, 211-214

Abstract: Abstract The discovery of a radioactively powered kilonova associated with the binary neutron-star merger GW170817 remains the only confirmed electromagnetic counterpart to a gravitational-wave event1,2. Observations of the late-time electromagnetic emission, however, do not agree with the expectations from standard neutron-star merger models. Although the large measured ejecta mass3,4 could be explained by a progenitor system that is asymmetric in terms of the stellar component masses (that is, with a mass ratio q of 0.7 to 0.8)5, the known Galactic population of merging double neutron-star systems (that is, those that will coalesce within billions of years or less) has until now consisted only of nearly equal-mass (q > 0.9) binaries6. The pulsar PSR J1913+1102 is a double system in a five-hour, low-eccentricity (0.09) orbit, with an orbital separation of 1.8 solar radii7, and the two neutron stars are predicted to coalesce in $${470}_{-11}^{+12}$$470−11+12 million years owing to gravitational-wave emission. Here we report that the masses of the pulsar and the companion neutron star, as measured by a dedicated pulsar timing campaign, are 1.62 ± 0.03 and 1.27 ± 0.03 solar masses, respectively. With a measured mass ratio of q = 0.78 ± 0.03, this is the most asymmetric merging system reported so far. On the basis of this detection, our population synthesis analysis implies that such asymmetric binaries represent between 2 and 30 per cent (90 per cent confidence) of the total population of merging binaries. The coalescence of a member of this population offers a possible explanation for the anomalous properties of GW170817, including the observed kilonova emission from that event.

Date: 2020
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DOI: 10.1038/s41586-020-2439-x

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