Gravitational waves or deconfined quarks: What causes the premature collapse of neutron stars born in short gammaray bursts?
Abstract
We infer the collapse times of longlived neutron stars into black holes using the xray afterglows of 18 short gammaray bursts. We then apply hierarchical inference to infer properties of the neutron star equation of state and dominant spindown mechanism. We measure the maximum nonrotating neutron star mass M_{TOV}=2.3 1_{0.21}^{+0.36}M_{☉} and constrain the fraction of remnants spinning down predominantly through gravitationalwave emission to η =0.6 9_{0.39}^{+0.21} with 68% uncertainties. In principle, this method can determine the difference between hadronic and quark equation of states. In practice, however, the data is not yet informative with indications that these neutron stars do not have hadronic equation of states at the 1 σ level. These inferences all depend on the underlying progenitor mass distribution for short gammaray bursts produced by binary neutron star mergers. The recently announced gravitationalwave detection of GW190425 suggests this underlying distribution is different from the locally measured population of double neutron stars. We show that M_{TOV} and η constraints depend on the fraction of binary mergers that form through a distribution consistent with the locally measured population and a distribution that can explain GW190425. The more binaries that form from the latter distribution, the larger M_{TOV} needs to be to satisfy the xray observations. Our measurements above are marginalized over this unknown fraction. If instead, we assume GW190425 is not a binary neutron star merger, i.e., the underlying mass distribution of double neutron stars is the same as observed locally, we measure M_{TOV}=2.2 6_{0.17}^{+0.31}M_{☉}.
 Publication:

Physical Review D
 Pub Date:
 March 2020
 DOI:
 10.1103/PhysRevD.101.063021
 arXiv:
 arXiv:2001.06102
 Bibcode:
 2020PhRvD.101f3021S
 Keywords:

 Astrophysics  High Energy Astrophysical Phenomena;
 General Relativity and Quantum Cosmology;
 Nuclear Theory
 EPrint:
 Published in Phys. Rev. D: Vol 101, Issue 6