  We perform the first reflection study of the soft X-ray transient and Type 1
burst source XTE J1709-267 using NuSTAR observations during its 2016 June
outburst. There was an increase in flux near the end of the observations, which
corresponds to an increase from $\sim$0.04 L$_{\mathrm{Edd}}$ to $\sim$0.06
L$_{\mathrm{Edd}}$ assuming a distance of 8.5 kpc. We have separately examined
spectra from the low and high flux intervals, which were soft and show evidence
of a broad Fe K line. Fits to these intervals with relativistic disk reflection
models have revealed an inner disk radius of $13.8_{-1.8}^{+3.0}\ R_{g}$ (where
$R_{g} = GM/c^{2}$) for the low flux spectrum and $23.4_{-5.4}^{+15.6}\ R_{g}$
for the high flux spectrum at the 90\% confidence level. The disk is likely
truncated by a boundary layer surrounding the neutron star or the
magnetosphere. Based on the measured luminosity and using the accretion
efficiency for a disk around a neutron star, we estimate that the theoretically
expected size for the boundary layer would be $\sim0.9-1.1 \ R_{g}$ from the
neutron star's surface, which can be increased by spin or viscosity effects.
Another plausible scenario is that the disk could be truncated by the
magnetosphere. We place a conservative upper limit on the strength of the
magnetic field at the poles, assuming $a_{*}=0$ and $M_{NS}=1.4\ M_{\odot}$, of
$B\leq0.75-3.70\times10^{9}$ G, though X-ray pulsations have not been detected
from this source.
