The soft-X-ray emission of Ark 120. XMM-Newton, NuSTAR, and the importance of taking the broad view
Harrison, F. A.; Stern, D.; Zhang, W. W.; Cappi, M.; Guainazzi, M.; Fabian, A. C.; Reynolds, C. S.; Elvis, M.; Lohfink, A.; Matt, G.; Boggs, S. E.; Christensen, F. E.; Craig, W. W.; Hailey, C. J.; Walton, D. J.; Marinucci, A.; Brenneman, L. W.; Fuerst, F.; Parker, M.; Arèvalo, P.
Italy, Spain, United States, Chile, Denmark, United Kingdom
Abstract
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 disc 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.