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We present broad-band, multi-epoch X-ray spectroscopy of the pulsatingultra-luminous X-ray source (ULX) in NGC 5907. Simultaneous XMM-Newton andNuSTAR data from 2014 are best described by a multi-color black-body model witha temperature gradient as a function of accretion disk radius significantlyflatter than expected for a standard thin accretion disk (T(r) ~ r^{-p}, withp=0.608^{+0.014}_{-0.012}). Additionally, we detect a hard power-law tail atenergies above 10 keV, which we interpret as being due to Comptonization. Wecompare this observation to archival XMM-Newton, Chandra, and NuSTAR data from2003, 2012, and 2013, and investigate possible spectral changes as a functionof phase over the 78d super-orbital period of this source. We find thatobservations taken around phases 0.3-0.4 show very similar temperatureprofiles, even though the observed flux varies significantly, while oneobservation taken around phase 0 has a significantly steeper profile. Wediscuss these findings in light of the recent discovery that the compact objectis a neutron star and show that precession of the accretion disk or the neutronstar can self-consistently explain most observed phenomena.

Spectral Changes in the Hyperluminous Pulsar in NGC 5907 as a Function of Super-Orbital Phase