The Environment of the Binary Neutron Star Merger GW170817

Abstract

We present Hubble Space Telescope (HST) and Chandra imaging, combined with Very Large Telescope MUSE integral field spectroscopy of the counterpart and host galaxy of the first binary neutron star merger detected via gravitational-wave emission by LIGO and Virgo, GW170817. The host galaxy, NGC 4993, is an S0 galaxy at z=0.009783. There is evidence for large, face-on spiral shells in continuum imaging, and edge-on spiral features visible in nebular emission lines. This suggests that NGC 4993 has undergone a relatively recent ( 1  Gyr) "dry" merger. This merger may provide the fuel for a weak active nucleus seen in Chandra imaging. At the location of the counterpart, HST imaging implies there is no globular or young stellar cluster, with a limit of a few thousand solar masses for any young system. The population in the vicinity is predominantly old with 1% of any light arising from a population with ages 500 Myr < . Both the host galaxy properties and those of the transient location are consistent with the distributions seen for short-duration gamma-ray bursts, although the source position lies well within the effective radius (r 3 e~k pc), providing an r e -normalized offset that is closer than 90% of short GRBs. For the long delay time implied by the stellar population, this suggests that the kick velocity was significantly less than the galaxy escape velocity. We do not see any narrow host galaxy interstellar medium features within the counterpart spectrum, implying low extinction, and that the binary may lie in front of the bulk of the host galaxy.

Fast Radio Bursts from Activity of Neutron Stars Newborn in BNS Mergers: Offset, Birth Rate, and Observational Properties

“…In the calculations, we average over all possible orientations of host galaxies. The observed offsets of GW170817/GRB 170817A (2 kpc) (Levan et al 2017), FRB 180924 (4 kpc) (Bannister et al 2019), FRB 180916 (4.7 kpc) (Marcote et al 2020) and FRB 190523 (29 kpc) and offsets distribution of short GRBs (Fong et al 2010(Fong et al , 2013Berger 2014) are also shown for comparison. For massive spiral galaxies (α = 1), 60% NS-NS systems will have offsets larger than 10 kpc.…”

The Masses of Isolated Neutron Stars Inferred from the Gravitational Redshift Measurements

“…For the case of GW170817, we fix the source location to the known position (R.A. = 197.450374 • , Decl. = −23.381495 • , z c = 0.0099) as determined by electromagnetic (EM) observations (Abbott et al 2017;Levan et al 2017) following Abbott et al (2019a), and assume the spin of each NS is aligned with the orbital angular momentum. We further marginalize the likelihood over coalescence phase (assuming that the signal is dominated by the l = 2, |m| = 2 modes) and the luminosity distance to accelerate Nest sampling (Allen et al 2012;Abbott et al 2019a;Radice & Dai 2019;Thrane & Talbot 2019).…”

The Equation of State and Some Key Parameters of Neutron Stars: Constraints from GW170817, the Nuclear Data, and the Low-mass X-Ray Binary Data

“…where M c is chirp mass and q is mass ratio. Note that here M 1 and M 2 are detector frame parameters, but we can just calculate the source frame masses through parameterized EoSs, so we optimize central enthalpy h c1 and h c2 to get M 1 /(1 + z) and M 2 /(1 + z), respectively, where z = 0.0099 is the geocentric redshift of the source of GW170817 (Levan et al 2017; inferred from the electromagnetic observations of the host galaxy NGC4993. Then we can combine four pressure parameters and optimized central enthalpy h opt c1 (h opt c2 ) to calculate Λ 1 (Λ 2 ).…”