Black hole-neutron star coalescence: Effects of the neutron star spin on jet launching and dynamical ejecta mass

Black hole-neutron star (BHNS) mergers are thought to be sources of gravitational waves (GWs) with coincident electromagnetic (EM) counterparts. To further probe whether these systems are viable progenitors of short gamma-ray bursts (SGRBs) and kilonovas, and how one may use (the lack of) EM counterparts associated with LIGO/Virgo candidate BHNS GW events to sharpen parameter estimation, we study the impact of neutron star spin in BHNS mergers. Using dynamical spacetime magnetohydrodynamic simulations of BHNSs initially on a quasicircular orbit, we survey configurations that differ in the BH spin (a(BH)/M-BH = 0 and 0.75), the NS spin (a(NS)/M-NS = -0.17, 0, 0.23, and 0.33), and the binary mass ratio (q = (MBHMNS)-M- = 3 :1 and 5:1). The general trend we find is that increasing the NS prograde spin increases both the rest mass of the accretion disk onto the remnant black hole, and the rest mass of dynamically ejected matter. By a time Delta t similar to 3500-5500M similar to 88-138(M-NS/1.4 M-circle dot) ms after the peak gravitational-wave amplitude, a magnetically driven jet is launched only for q = 3:1 regardless of the initial NS spin. The lifetime of the jets [At X 0.5-0.8(M HB /1.4 M-circle dot) s] and their outgoing Poynting luminosity [L-Poyn similar to 10(513 +/- 03) erg/s] are consistent with typical SGRBs' luminosities and expectations from the Blandford-Znajek mechanism. By the time we terminate our simulations, we do not observe either an outflow or a large-scale magnetic-field collimation for the other systems we consider. The mass range of dynamically ejected matter is 10(-43) -10(-2) (MNs / 1 . 4 M-circle dot) M-circle dot, which can power kilonovas with peak bolometric luminosities L-knova similar to 10(40)-10(41.4) erg/s with rise times less than or similar to 6.5 h and potentially detectable by the LSST.