  Binary neutron star (BNS) mergers are the leading model to explain the
phenomenology of short gamma-ray bursts (SGRBs), which are among the most
luminous explosions in the universe. Recent observations of long-lasting X-ray
afterglows of SGRBs challenge standard paradigms and indicate that in a large
fraction of events a long-lived neutron star (NS) may be formed rather than a
black hole. Understanding the mechanisms underlying these afterglows is
necessary in order to address the open questions concerning the nature of SGRB
central engines. However, recent theoretical progress has been hampered by the
fact that the timescales of interest for the afterglow emission are
inaccessible to numerical relativity simulations. Here we present a detailed
model to bridge the gap between numerical simulations of the merger process and
the relevant timescales for the afterglows, assuming that the merger results in
a long-lived NS. This model is formulated in terms of a set of coupled
differential equations that follow the evolution of the post-merger system and
predict its electromagnetic (EM) emission in a self-consistent way, starting
from initial data that can be extracted from BNS merger simulations and taking
into account the most relevant radiative processes. Moreover, the model can
accomodate the collapse of the remnant NS at any time during the evolution as
well as different scenarios for the prompt SGRB emission. A second major reason
of interest for BNS mergers is that they are considered the most promising
source of gravitational waves (GWs) for detection with the advanced
ground-based detector network LIGO/Virgo coming online this year.
Multimessenger astronomy with joint EM and GW observations of the merger and
post-merger phase can greatly enhance the scientific output of either type of
observation. However, the actual benefit depends on ...
