  The Accreting Millisecond X-ray Pulsar IGR J17591-2342 is a LMXB system that
went in outburst on August 2018 and it was monitored by the NICER observatory
and partially by other facilities. We aim to study how the spectral emission of
this source evolved during the outburst, by exploiting the whole X-ray data
repository of simultaneous observations. The continuum emission of the combined
broad-band spectra is on average well described by an absorbed Comptonisation
component scattering black-body-distributed photons peaking at (0.8+/-0.5) keV,
by a moderately optically thick corona (tau=2.3+/-0.5) with temperature of
(34+/-9) keV. A black-body component with temperature and radial size of
(0.8+/-0.2) keV and (3.3+/-1.5) km respectively is required by some of the
spectra and suggests that part of the central emission, possibly a fraction of
the neutron star surface, is not efficiently scattered by the corona. The
continuum at low energies is characterised by significant residuals suggesting
the presence of an absorption edge of O VIII and of emission lines of Ne IX
ions. Moreover, broad Fe I and Fe XXV K-alpha emission lines are detected at
different times of the outburst, suggesting the presence of reflection in the
system.
