The soft X-ray emission of Ark 120. XMM-Newton, NuSTAR, and the   importance of taking the broad view
  We present simultaneous XMM-Newton and NuSTAR observations of the `bare' Seyfert 1 galaxy, Ark 120, a system in which ionized absorption is absent. The NuSTAR hard X-ray spectral coverage allows us to constrain different models for the excess soft X-ray emission. Among phenomenological models, a cutoff power law best explains the soft X-ray emission. This model likely corresponds to Comptonization of the accretion disk seed UV photons by a population of warm electrons: using Comptonization models, a temperature of ~0.3 keV and an optical depth of ~13 are found. If the UV-to-X-ray optxagnf model is applied, the UV fluxes from the XMM-$Newton$ Optical Monitor suggest an intermediate black hole spin. Contrary to several other sources observed by NuSTAR, no high energy cutoff is detected, with a lower limit of 190 keV. 
G. Matt, A. Marinucci, M. Guainazzi, L.W. Brenneman, M. Elvis, A.   Lohfink, P. Arevalo, S.E. Boggs, M. Cappi, F.E. Christen...
astro-ph.HE