TITLE:   GCN CIRCULAR
NUMBER:  24420
SUBJECT: LIGO/Virgo S190426c (BHNS candidate): Implications from Numerical Relativity
DATE:    19/05/07 18:39:37 GMT
FROM:    Antonios Tsokaros at U of Illinois,Urbana-Champaign  <tsokaros@illinois.edu>

LIGO/Virgo S190426c (BHNS candidate): Implications from Numerical Relativity

M. Ruiz, S. L. Shapiro and A. Tsokaros
report on behalf of the Illinois Relativity Group


Consistent with GCN 24411, indicating that the LIGO/Virgo gravitational
wave source S190426c is a likely BHNS, the absence of a gamma-ray burst,
kilonova and other counterpart EM radiation agrees with recent GRMHD
simulations of BHNS mergers by our Illinois Relativity Group. In
Ruiz, Shapiro and Tsokaros (2018), PRD 98, 123017 (arXiv 1810.08618), the
group surveyed BHNS configurations with different initial mass ratios
q=BH:NS=3:1 and 5:1, BH spins a_{BH}/M_{BH}=-0.5, 0, 0.5, 0.75 and dipole
magnetic fields (aligned and tilted by 90 degrees with respect to the
orbital angular momentum). Only for initial a_{BH}/M_{BH}>=0.5 and
aligned B-fields did we find collimated, magnetically-confined jets
launched from the poles of the BH remnants following the peak GW signal.
Only in those cases did we find EM luminosities consistent with typical
sGRBs and significant mass outflows. For example, in our case q=5:1 and
a_{BH}/M_{BH}=0 the remnant disk and magnetic field were too small to
drive a jet and generate a significant mass outflow or counterpart EM
luminosity, hence no sGRB or kilonova.