Numerical relativity simulations of the neutron star merger GW190425: microphysics and mass ratio effects
In 2204.05336 we simulate 28 BNS mergers with the chirp mass of GW190425 and spanning a mass ratio 1≤q≤1.67, using finite temperature, composition dependent nuclear equation of state (EOS) and neutrino radiation. We focus on the merger outcome and on possible kilonova counterparts that were not observed during follow-ups (because too dim or the source’s localisation area too broad). The energy emitted in GWs is ≲0.083M⊙c^2 with a peak luminosity of 1.1−2.4×1058erg/s/(1+q)^2. Dynamical ejecta and disc mass are relatively small, the former ranging between 5×10−6 and ∼10−3 M⊙ and the latter between 10−5 and 0.1 M⊙. Asymmetric mergers, especially in the case of stiff EOS, are able to unbind more matter and to form heavier discs compared to equal mass binaries. The angular momentum of the disc is 8−10M⊙ GMdisc/c over three orders of magnitude in Mdisc. While the associated nucleosynthesis shows no peculiarity, the simulated kilonovae are relatively dim compared to the GW170817 event. In particular, for distances compatible with GW190425, we find AB magnitudes always dimmer than ∼20 mag for the B, r and K bands, with brighter kilonovae associated to more asymmetric binaries and stiffer EOS. We suggest that, even assuming a good coverage of GW190425’s sky location, the kilonova signal could hardly have been detected by present wide-field surveys and no firm constraints on the binary parameters or neutron star EOS can be argued from the lack of the detection
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