1RXS J180408.9–342058 is a transient neutron star low-mass X-ray binary that exhibited a bright accretion outburst in 2015 .
We present NuSTAR , Swift , and Chandra observations obtained around the peak brightness of this outburst .
The source was in a soft X-ray spectral state and displayed an X-ray luminosity of L _ { \mathrm { X } } \simeq ( 2 - 3 ) \times 10 ^ { 37 } ~ { } ( D / 5.8 ~ { } \mathrm { kpc } ) ^ { 2 } ~ { } \mathrm { erg~ { } s } ^ { -1 } ( 0.5–10 keV ) .
The NuSTAR data reveal a broad Fe-K emission line that we model as relativistically broadened reflection to constrain the accretion geometry .
We found that the accretion disk is viewed at an inclination of i \simeq 27 ^ { \circ } – 35 ^ { \circ } and extended close to the neutron star , down to R _ { \mathrm { in } } \simeq 5–7.5 gravitational radii ( \simeq 11–17 km ) .
This inner disk radius suggests that the neutron star magnetic field strength is B \lesssim 2 \times 10 ^ { 8 } G. We find a narrow absorption line in the Chandra /HEG data at an energy of \simeq 7.64 keV with a significance of \simeq 4.8 \sigma .
This feature could correspond to blue-shifted Fe xxvi and arise from an accretion disk wind , which would imply an outflow velocity of v _ { \mathrm { out } } \simeq 0.086 c ( \simeq 25 800 ~ { } \mathrm { km~ { } s } ^ { -1 } ) .
However , this would be extreme for an X-ray binary and it is unclear if a disk wind should be visible at the low inclination angle that we infer from our reflection analysis .
Finally , we discuss how the X-ray and optical properties of 1RXS J180408.9–342058 are consistent with a relatively small ( P _ { \mathrm { orb } } \lesssim 3 hr ) binary orbit .