The association of GRB170817A with GW170817 has confirmed the long-standing hypothesis that binary neutron star (BNS) mergers are the progenitors of at least some short gamma-ray bursts (SGRBs). This connection has ushered in an era in which broadband observations of SGRBs, together with measurements of the time delay between the gravitational waves and the electromagnetic radiation, allow for probing the properties of the emitting outflow and its engine to an unprecedented detail. Because the structure of the radiating outflow is molded by the interaction of a relativistic jet with the binary ejecta, it is of paramount importance to study the system in a realistic setting. Here we present a three-dimensional hydrodynamic simulation of a relativistic jet propagating in the ejecta of a BNS merger, which were computed with a general relativistic magnetohydrodynamic simulation. We find that the jet’s centroid oscillates around the axis of the system, due to inhomogeneities encountered in the propagation. These oscillations allow the jet to find the path of least resistance and travel faster than an identical jet in smooth ejecta. In our setup the breakout time is ∼0.6 s, which is comparable to the expected central engine duration in SGRBs and possibly a non-negligible fraction of the total delay between the gravitational and gamma-ray signals. Our simulation also shows that energy is carried in roughly equal amounts by the jet and by the cocoon, and that about 20% of the injected energy is transferred to the ejecta via mechanical work.
- NSF-PAR ID:
- 10351649
- Date Published:
- Journal Name:
- Annual Review of Astronomy and Astrophysics
- Volume:
- 59
- Issue:
- 1
- ISSN:
- 0066-4146
- Page Range / eLocation ID:
- 155 to 202
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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ABSTRACT The association of GRB170817A with a binary neutron star (BNS) merger has revealed that BNSs produce at least a fraction of short gamma-ray 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 broad-band 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 GW-triggered events. We find a gamma-ray 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, GW-triggered aligned case. Afterglow detection probabilities of GW-triggered 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 low-energy bands, unlike gamma-ray-triggered events (cosmological SGRBs) which are significantly brighter at higher energies. We further quantify observational biases with respect to host galaxy masses.
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1146/annurev-astro-112420-030742
