The association of GRB170817A with a binary neutron star (BNS) merger has revealed that BNSs produce at least a fraction of short gammaray bursts (SGRBs). As gravitational wave (GW) detectors push their horizons, it is important to assess coupled electromagnetic (EM)/GW probabilities and maximize observational prospects. Here, we perform BNS population synthesis calculations with the code mobse, seeding the binaries in galaxies at three representative redshifts, $z$ = 0.01, 0.1, and 1 of the Illustris TNG50 simulation. The binaries are evolved and their locations numerically tracked in the host galactic potentials until merger. Adopting the microphysics parameters of GRB170817A, we numerically compute the broadband light curves of jets from BNS mergers, with the afterglow brightness dependent on the local medium density at the merger site. We perform Monte Carlo simulations of the resulting EM population assuming either a random viewing angle with respect to the jet, or a jet aligned with the orbital angular momentum of the binary, which biases the viewing angle probability for GWtriggered events. We find a gammaray detection probability of $\sim\!2{{\rm per\ cent}},10{{\rm per\ cent}},\mathrm{and}\ 40{{\rm per\ cent}}$ for BNSs at $z$ = 1, 0.1, and 0.01, respectively, for the random case, rising to $\sim\!75{{\rm per\ cent}}$ for the $z$ = 0.01, GWtriggered aligned case. Afterglow detection probabilities of GWtriggered BNS mergers vary in the range of $\sim \! 0.3 \!\! 0.5{{\rm per\ cent}}$, with higher values for aligned jets, and are comparable across the high and lowenergy bands, unlike gammaraytriggered events (cosmological SGRBs) which are significantly brighter at higher energies. We further quantify observational biases with respect to host galaxy masses.
The binary neutron star (BNS) mass distribution measured with gravitationalwave observations has the potential to reveal information about the dense matter equation of state, supernova physics, the expansion rate of the Universe, and tests of general relativity. As most current gravitationalwave analyses measuring the BNS mass distribution do not simultaneously fit the spin distribution, the implied populationlevel spin distribution is the same as the spin prior applied when analysing individual sources. In this work, we demonstrate that introducing a mismatch between the implied and true BNS spin distributions can lead to biases in the inferred mass distribution. This is due to the strong correlations between the measurements of the mass ratio and spin components aligned with the orbital angular momentum for individual sources. We find that applying a lowspin prior that excludes the true spin magnitudes of some sources in the population leads to significantly overestimating the maximum neutron star mass and underestimating the minimum neutron star mass at the population level with as few as six BNS detections. The safest choice of spin prior that does not lead to biases in the inferred mass distribution is one that allows for high spin magnitudes and tilts misaligned with the orbital angular momentum.
more » « less NSFPAR ID:
 10363180
 Publisher / Repository:
 Oxford University Press
 Date Published:
 Journal Name:
 Monthly Notices of the Royal Astronomical Society
 Volume:
 511
 Issue:
 3
 ISSN:
 00358711
 Page Range / eLocation ID:
 p. 43504359
 Format(s):
 Medium: X
 Sponsoring Org:
 National Science Foundation
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