Fürst, F.F.FürstWalton, D. J.D. J.WaltonStern, D.D.SternBACHETTI, MatteoMatteoBACHETTIBarret, D.D.BarretBrightman, M.M.BrightmanHarrison, F. A.F. A.HarrisonRana, V.V.Rana2021-04-212021-04-2120170004-637Xhttp://hdl.handle.net/20.500.12386/30820We present broadband, multi-epoch X-ray spectroscopy of the pulsating ultra-luminous X-ray source (ULX) in NGC 5907. Simultaneous XMM-Newton and NuSTAR data from 2014 are best described by a multicolor blackbody model with a temperature gradient as a function of accretion disk radius significantly flatter than expected for a standard thin accretion disk (T(r)\propto r-p, with p=0.608-0.012+0.014). Additionally, we detect a hard power-law tail at energies above 10 keV, which we interpret as being due to Comptonization. We compare this observation to archival XMM-Newton, Chandra, and NuSTAR data from 2003, 2012, and 2013, and investigate possible spectral changes as a function of phase over the 78-day super-orbital period of this source. We find that observations taken around phases 0.3-0.4 show very similar temperature profiles, even though the observed flux varies significantly, while one observation taken around phase 0 has a significantly steeper profile. We discuss these findings in light of the recent discovery that the compact object is a neutron star and show that precession of the accretion disk or the neutron star can self-consistently explain most observed phenomena.STAMPAenArticle10.3847/1538-4357/834/1/772-s2.0-85010042323https://iopscience.iop.org/article/10.3847/1538-4357/834/1/772017ApJ...834...77FFIS/05 - ASTRONOMIA E ASTROFISICAERC sectors::Physical Sciences and Engineering::PE9 Universe sciences: astro-physics/chemistry/biology; solar systems; stellar, galactic and extragalactic astronomy, planetary systems, cosmology, space science, instrumentation::PE9_10 High energy and particle astronomy – X-rays, cosmic rays, gamma rays, neutrinos