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 multi-wavelength 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 these modeling 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 a too massive accretion disk if the duration of the central engine activity is comparable to the observed $T_{90}$ of GRB 170817A, unless the timescale of the central engine activity is less than $\sim$ 0.2s. We propose that the GRB observations are helpful to constrain the combined tidal parameter $\tilde{\Lambda}$, and by adopting the accretion disk mass distribution estimated in BZ mechanism, the $90\%$ credible interval of $\tilde{\Lambda}$ for the progenitor of GW170817 is inferred as $309-954$.