Constraining the Maximum Mass of Neutron Stars From Multi-Messenger Observations of GW170817

Ben Margalit; Brian Metzger

doi:10.3847/2041-8213/aa991c

paper

Constraining the Maximum Mass of Neutron Stars From Multi-Messenger Observations of GW170817

arXiv:1710.05938 · doi:10.3847/2041-8213/aa991c

Abstract

We combine electromagnetic (EM) and gravitational wave (GW) information on the binary neutron star (NS) merger GW170817 in order to constrain the radii $R_{ns}$ and maximum mass $M_{max}$ of NSs. GW170817 was followed by a range of EM counterparts, including a weak gamma-ray burst (GRB), kilonova (KN) emission from the radioactive decay of the merger ejecta, and X-ray/radio emission consistent with being the synchrotron afterglow of a more powerful off-axis jet. The type of compact remnant produced in the immediate merger aftermath, and its predicted EM signal, depend sensitively on the high-density NS equation of state (EOS). For a soft EOS which supports a low $M_{max}$ , the merger undergoes a prompt collapse accompanied by a small quantity of shock-heated or disk wind ejecta, inconsistent with the large quantity $≳ 1 0^{- 2} M_{⊙}$ of lanthanide-free ejecta inferred from the KN. On the other hand, if $M_{max}$ is sufficiently large, then the merger product is a rapidly-rotating supramassive NS (SMNS), which must spin-down before collapsing into a black hole. A fraction of the enormous rotational energy necessarily released by the SMNS during this process is transferred to the ejecta, either into the GRB jet (energy $E_{GRB}$ ) or the KN ejecta (energy $E_{ej}$ ), also inconsistent with observations. By combining the total binary mass of GW170817 inferred from the GW signal with conservative upper limits on $E_{GRB}$ and $E_{ej}$ from EM observations, we constrain the likelihood probability of a wide-range of previously-allowed EOS. These two constraints delineate an allowed region of the $M_{max} - R_{ns}$ parameter space, which once marginalized over NS radius places an upper limit of $M_{max} ≲ 2.17 M_{⊙}$ (90\%), which is tighter or arguably less model-dependent than other current constraints.

arXiv commentApJL, accepted version

Constraining the Maximum Mass of Neutron Stars From Multi-Messenger Observations of GW170817

Abstract

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