An Iron K Component to the Ultrafast Outflow in NGC 1313 X-1

We present the detection of an absorption feature at $E$ = 8.77$^{+0.05}_{-0.06}$ keV in the combined X-ray spectrum of the ultraluminous X-ray source NGC 1313 X-1 observed with $\textit{XMM-Newton}$ and $\textit{NuSTAR}$, significant at the 3$\sigma$ level. If associated with blueshifted ionized iron, the implied outflow velocity is ~0.2$c$ for Fe XXVI, or ~0.25$c$ for Fe XXV. These velocities are similar to the ultrafast outflow seen in absorption recently discovered in this source at lower energies by $\textit{XMM-Newton}$, and we therefore conclude that this is an iron component to the same outflow. Photoionization modeling marginally prefers the Fe XXV solution, but in either case the outflow properties appear to be extreme, potentially supporting a super-Eddington hypothesis for NGC 1313 X-1.
M.J.M. acknowledges support from an STFC Ernest Rutherford fellowship, C.P. and A.C.F. acknowledge support from ERC Advanced Grant 340442, and D.B. acknowledges financial support from the French Space Agency (CNES). This research has made use of data obtained with NuSTAR, a project led by Caltech, funded by NASA, and managed by NASA/JPL, and has utilized the NUSTARDAS software package, jointly developed by the ASDC (Italy) and Caltech (USA). This research has also made use of data obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States.