NuSTAR/XMM-Newton monitoring of the Seyfert 1 galaxy HE 1143-1810.
  Testing the two-corona scenario
  We test the two-corona accretion scenario for active galactic nuclei in the
case of the `bare' Seyfert 1 galaxy HE 1143-1810. We perform a detailed study
of the broad-band UV--X-ray spectral properties and of the short-term
variability. We present results of a joint XMM-Newton and NuSTAR monitoring of
the source, consisting of 5x20 ks observations, each separated by 2 days,
performed in December 2017. The source is variable in flux among the different
observations, and a correlation is observed between the UV and X-ray emission.
Moderate spectral variability is observed in the soft band. The time-averaged
X-ray spectrum exhibits a cut-off at $\sim 100$ keV consistent with thermal
Comptonization. We detect an iron K$\alpha$ line consistent with being constant
during the campaign and originating from a mildly ionized medium. The line is
accompanied by a moderate, ionized reflection component. A soft excess is
clearly present below 2 keV and is well described by thermal Comptonization in
a `warm' corona with a temperature of $\sim 0.5$ keV and a Thomson optical
depth of $\sim 17-18$. For the hot hard X-ray emitting corona, we obtain a
temperature of $\sim 20$ keV and an optical depth of $\sim 4$ assuming a
spherical geometry. A fit assuming a jet-emitting disc (JED) for the hot corona
also provides a nice description of the broad-band spectrum. In this case, the
data are consistent with an accretion rate varying between $\sim 0.7$ and $\sim
0.9$ in Eddington units and a transition between the outer standard disc and
the inner JED at $\sim 20$ gravitational radii. The broad-band high-energy data
agree with an accretion flow model consisting of two phases: an outer standard
accretion disc with a warm upper layer, responsible for the optical--UV
emission and the soft X-ray excess, and an inner slim JED playing the role of a
hard X-ray emitting hot corona.
