  The progenitor system of the compact binary merger GW190425 had a total mass
of $3.4^{+0.3}_{-0.1}$ M$_\odot$ (90th-percentile confidence region) as
measured from its gravitational wave signal. This mass is significantly
different from the Milky Way (MW) population of binary neutron stars (BNSs)
that are expected to merge in a Hubble time and from that of the first BNS
merger, GW170817. Here we explore the expected electromagnetic signatures of
such a system. We make several astrophysically motivated assumptions to further
constrain the parameters of GW190425. By simply assuming that both components
were NSs, we reduce the possible component masses significantly, finding $m_1 =
1.85^{+0.27}_{-0.19}$ M$_\odot$ and $m_2 = 1.47^{+0.16}_{-0.18}$ M$_\odot$.
However if the GW190425 progenitor system was a NS-black hole merger, we find
best-fitting parameters $m_1 = 2.19^{+0.21}_{-0.17}$ M$_\odot$ and $m_2 =
1.26^{+0.10}_{-0.08}$ M$_\odot$. For a well-motivated BNS system where the
lighter NS has a mass similar to the mass of non-recycled NSs in MW BNS
systems, we find $m_1 = 2.03^{+0.15}_{-0.14}$ M$_\odot$ and $m_2 = 1.35 \pm
0.09$ M$_\odot$, corresponding to only 7% mass uncertainties. For all
scenarios, we expect a prompt collapse of the resulting remnant to a black
hole. Examining detailed models with component masses similar to our
best-fitting results, we find the electromagnetic counterpart to GW190425 is
expected to be significantly redder and fainter than that of GW170817. We find
that almost all reported observations used to search for an electromagnetic
counterpart for GW190425 were too shallow to detect the expected counterpart.
If the LIGO-Virgo Collaboration promptly provides the chirp mass, the
astronomical community can adapt their observations to improve the likelihood
of detecting a counterpart for similarly "high-mass" BNS systems. (abridged)
