  The black hole candidate XTE J1908+094 went into outburst for the first time
since 2003 in October 2013. We report on an observation with the Nuclear
Spectroscopic Telescope Array (NuSTAR) and monitoring observations with Swift
during the outburst. NuSTAR caught the source in the soft state: the spectra
show a broad relativistic iron line, and the light curves reveal a ~40 ks flare
with the count rate peaking about 40% above the non-flare level and with
significant spectral variation. A model combining a multi-temperature thermal
component, a power-law, and a reflection component with an iron line provides a
good description of the NuSTAR spectrum. Although relativistic broadening of
the iron line is observed, it is not possible to constrain the black hole spin
with these data. The variability of the power-law component, which can also be
modeled as a Comptonization component, is responsible for the flux and spectral
change during the flare, suggesting that changes in the corona (or possibly
continued jet activity) are the likely cause of the flare.

High Energy Astrophysical Phenomena