Simulating short GRB jets in late binary neutron star merger environments

Abstract

The electromagnetic emission and the afterglow observations of the binary neutron star merger event GW 170817A confirmed the association of the merger with a short gamma-ray burst (sGRB) harboring a narrow ($5$°-$10$°) and powerful ($10^{49}$-$10^{50}$erg) jet. Using the 1~second-long neutrino-radiation-GR-MHD simulation of coalescing neutron stars of Kiuchi et al. (2023) and following the semi-analytical estimates of Pais et al. (2023), we inject a narrow, powerful, unmagnetized jet into the post-merger phase. We explore different opening angles, luminosities, central engine durations, and times after the merger. We explore early ($0.1$s following the merger) and late ($1$s) jet launches; the latter is consistent with the time delay of $\approx 1.74$s observed between GW 170817 and GRB 170817A. We demonstrate that the semi-analytical estimates correctly predict the jets' breakout and collimation conditions. When comparing our synthetic afterglow light curves to the observed radio data of GW170807, we find a good agreement for a $3\times 10^{49}$ ergs jet launched late with an opening angle in the range $\simeq 5$°-$7$°.

25 pages, 17 figures, 2 tables. Accepted for publication on ApJ, minor corrections