  Binary neutron star (NS) mergers with their subsequent fast-rotating
supramassive magnetars are one attractive interpretation for at least some
short gamma-ray bursts (SGRBs), based on the internal plateau commonly observed
in the early X-ray afterglow. The rapid decay phase in this scenario signifies
the epoch when the star collapses to a black hole after it spins down, and
could effectively shed light on the underlying unclear equation of state (EoS)
of dense matter. In the present work, we confront the protomagnetar masses of
the internal plateau sample from representative EoS models, with the one
independently from the observed galactic NS-NS binary, aiming to contribute new
compact star EoSs from SGRB observations. For this purpose, we employ various
EoSs covering a wide range of maximum mass for both NSs and quark stars (QSs),
and in the same time satisfying the recent observational constraints of the two
massive pulsars whose masses are precisely measured (around $2 M_{\odot}$). We
first illustrate that how well the underlying EoS would reconcile with the
current posterior mass distribution, is largely determined by the static
maximum mass of that EoS. We then construct 3 new postmerger QS EoSs (PMQS1,
PMQS2, PMQS3), respecting fully the observed distribution. We also provide
easy-to-use parameterizations for both the EoSs and the corresponding maximum
gravitational masses of rotating stars. In addition, we calculate the fractions
of postmerger products for each EoS, and discuss potential consequences for the
magnetar-powered kilonova model.
