Fermi Gamma-ray Space Telescope

Location and Environments of Neutron Star Mergers in an Evolving Universe

Dieter Hartmann
(Wiggins, Brandon K.; Fryer, Christopher L.; Smidt, Joseph M.; Lloyd-Ronning, Nicole; Belcynski, Chris)


The simultaneous detection of GW and EM waves from a binary neutron star merger has both solidified the link between neutron star mergers and short-duration GRBs and demonstrated the ability of astronomers to follow-up the gravitational wave detection to place constraints on ejecta as well as merger surroundings. As the sensitivity of aLIGO and VIRGO increases, a growing event sample allow us to constrain populations. While long-duration GRBs originate from massive stars and thus are located near their stellar nurseries, binary neutron stars may merge on much longer timescales, and thus may have had time to migrate appreciably. The strength and character of the electromagnetic afterglow emission of binary neutron star mergers is a sensitive function of the circum-merger environment. Though the explosion sites of short GRBs have been explored in the literature, this aspect needed to be more fully addressed in its cosmological context. We present cosmological simulations following the evolution of a galaxy cluster, including star formation combined with binary population synthesis models to self-consistently track the locations and environmental gas densities of merger sites throughout the cosmic web. We present probability distributions for densities as a function of redshift.