GW170817: The Energy Extraction Process of the Off-axis Relativistic Outflow and the Constraint on the Equation of State of Neutron Stars

Abstract

As revealed recently by the modeling of the multiwavelength data of the emission following GW170817/GRB 170817A, there was an off-axis energetic relativistic outflow component launched by this historic double neutron star merger event. In this work we use the results of this model to examine the energy extraction process of the central engine. We show that the magnetic process (i.e., the Blandford–Znajek mechanism) is favored, while the neutrino process usually requires an accretion disk that is too massive if the duration of the central engine activity T act is comparable to the observed T 90 of GRB 170817A. If T act is less than ∼0.2 s, the two models are indistinguishable. We propose that the GRB observations are helpful to constrain the combined tidal parameter , and by adopting the accretion disk mass distribution estimated in the BZ mechanism, the 90% credible interval of for the progenitor of GW170817 is inferred as 309 − 954.