  On 2017 August 17 the merger of two compact objects with masses consistent
with two neutron stars was discovered through gravitational-wave (GW170817),
gamma-ray (GRB 170817A), and optical (SSS17a/AT 2017gfo) observations. The
optical source was associated with the early-type galaxy NGC 4993 at a distance
of just $\sim$40 Mpc, consistent with the gravitational-wave measurement, and
the merger was localized to be at a projected distance of $\sim$2 kpc away from
the galaxy's center. We use this minimal set of facts and the mass posteriors
of the two neutron stars to derive the first constraints on the progenitor of
GW170817 at the time of the second supernova (SN). We generate simulated
progenitor populations and follow the three-dimensional kinematic evolution
from the binary neutron star (BNS) birth to the merger time, accounting for
pre-SN galactic motion, for considerably different input distributions of the
progenitor mass, pre-SN semimajor axis, and SN-kick velocity. Though not
considerably tight, we find these constraints to be comparable to those for
Galactic BNS progenitors. The derived constraints are very strongly influenced
by the requirement of keeping the binary bound after the second SN and having
the merger occur relatively close to the center of the galaxy. These
constraints are insensitive to the galaxy's star formation history, provided
the stellar populations are older than 1 Gyr.
