Nustar and Xmm-newton Observations of the Neutron Star X-ray Binary 1rxs J180408.9-34205

We report on observations of the neutron star (NS) residing in the low-mass X-ray binary 1RXS J180408.934205 taken 2015 March by NuSTAR and XMM-Newton while the source was in the hard spectral state. We find multiple reflection features (Fe Kα detected with NuSTAR; N VII, O VII, and O VIII detected in the RGS) from different ionization zones. Through joint fits using the self consistent relativistic reflection model RELXILL, we determine the inner radius to be ≤ 11.1Rg. For a 1.4 M⊙ NS with a spin of a∗ = 0, this is an inner disk radius of ≤ 22.2 km. We find the inclination of the system to be between 18-29. If the disk is truncated at a radius greater than the neutron star radius, it could be truncated by a boundary layer on the neutron star surface. It is also possible that the disk is truncated at the magnetospheric radius; conservative estimates would then imply B ≤ (0.3 − 1.0) × 10 G at the magnetic poles, though coherent pulsations have not been detected and the source is not identified as a pulsar.