  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 $309-954$.
