Hydrodynamic evolution of neutron star merger remnants

Based on the special relativistic hydrodynamic equations and updated cooling function, we investigate the long-term evolution of neutron stars merger (NSM) remnants by a one-dimensional hydrodynamic code. Three NSM models from one soft equation of state, SFHo, and two stiff equations of state, DD2 and TM1, are used to compare their influences on the hydrodynamic evolution of remnants. We present the luminosity, mass and radius of remnants, as well as the velocity, temperature and density of shocks. For a typical interstellar medium (ISM) density with solar metallicity, we find that the NSM remnant from the SFHo model makes much more changes to ISM in terms of velocity, density and temperature distributions, compared with the case of DD2 and TM1 models. The maximal luminosity of the NSM remnant from the SFHo model is 3.4 x 10(38) erg s(-1), which is several times larger than that from DD2 and TM1 models. The NSM remnant from the SFHo model can maintain high luminosity (>10(38) erg s(-1)) for 2.29 x 10(4) yr. Furthermore, the density and temperature of remnants at the maximal luminosity are not sensitive to the power of the original remnant. For the ISM with the solar metallicity and n(H) = 1 cm(-3), the density of the first shock similar to 10(-23) g cm(-3) and the temperature similar to 3 x 10(5) K in the maximal luminosity phase; The temperature of the first shock decreases and there is a thin 'dense' shell with density similar to 10(-21) g cm(-3) after the maximal luminosity. These characteristics may be helpful for future observations of NSM remnants.