Description
A long-standing issue in X-ray studies of AGN is the nature of the "soft excess", an excess of flux seen below ~2keV when the standard AGN continuum that reproduces high-energy X-ray emission is extrapolated down in energy. One of the leading interpretations is that this feature is related to relativistic reflection from the accretion disc, resulting from a combination of relativistically broadened emission lines and the free-free continuum present in reflection models at low energies. To explore this further we present results from a deep, coordinated XMM+NuSTAR observation of the 'bare' type 1 Seyfert PG1426+015, a source of particular interest as the most massive reverberation-mapped black hole to date (log[M/Msun] = 9.0). The broadband spectrum unambiguously reveals the presence of relativistic reflection (broad iron emission, Compton reflection hump) as well as confirming the presence of the strong soft excess reported previously. We test whether relativistic reflection can successfully account for the soft excess along with the higher-energy reflection features, utilizing the two most-commonly used reflection codes (REFLIONX, XILLVER). Ultimately we find that both models are able to successfully reproduce the soft excess, though in the case of the XILLVER model this is contingent on reducing the strength of the OVIII line included in the model, as otherwise this feature prevents the model from reproducing the data. Though we focus on PG1426+015 as a test case, this OVIII issue likely has broader implications for recent attempts to explore the reflection model for the soft excess in AGN more generally.
