Constraining neutron star radii in black hole-neutron star mergers from
  their electromagnetic counterparts
  Mergers of black hole (BH) and neutron star (NS) binaries are of interest
since the emission of gravitational waves (GWs) can be followed by an
electromagnetic (EM) counterpart, which could power short gamma-ray bursts.
Until now, LIGO/Virgo has only observed a candidate BH-NS event,
GW190426\_152155, which was not followed by any EM counterpart. We discuss how
the presence (absence) of a remnant disk, which powers the EM counterpart, can
be used along with spin measurements by LIGO/Virgo to derive a lower (upper)
limit on the radius of the NS. For the case of GW190426\_152155, large
measurement errors on the spin and mass ratio prevent from placing an upper
limit on the NS radius. Our proposed method works best when the aligned
component of the BH spin (with respect to the orbital angular momentum) is the
largest, and can be used to complement the information that can be extracted
from the GW signal to derive valuable information on the NS equation of state.
