The first simultaneous X-ray broad-band view of Mrk 110 with XMM-Newton
  and NuSTAR
  (Abridged) Soft and hard X-ray excesses, compared to the continuum power-law
shape between ~2-10 keV, are common features observed in the spectra of active
galactic nuclei (AGN) and are associated with the accretion disc-corona system
around the supermassive black hole. However, the dominant process at work is
still highly debated and has been proposed to be either relativistic reflection
or Comptonisation. We aim to characterise the main X-ray spectral physical
components from the bright bare Broad Line Seyfert 1 AGN Mrk 110, and the
physical process(es) at work in its disc-corona system viewed almost face-on.
We perform the X-ray broad-band spectral analysis thanks to two simultaneous
XMM-Newton and NuSTAR observations performed on November 16-17 2019 and April
5-6 2020, we also use for the spectral analysis above 3 keV the deep NuSTAR
observation obtained in January 2017. The broad-band X-ray spectra of Mrk 110
are characterised by the presence of a prominent and absorption-free smooth
soft X-ray excess, moderately broad OVII and FeKalpha emission lines and a lack
of a strong Compton hump. The continuum above ~3keV is very similar at both
epochs, while some variability (stronger when brighter) is present for the soft
X-ray excess. A combination of soft and hard Comptonisation by a warm and hot
corona, respectively, plus mildly relativistic disc reflection reproduce the
broadband X-ray continuum very well. The inferred warm corona temperature,
kT_warm~0.3 keV, is similar to the values found in other sub-Eddington AGN,
whereas the hot corona temperature, kT_hot~21-31 keV (depending mainly on the
assumed hot corona geometry), is found to be in the lower range of the values
measured in AGN.
