Narrow Line Seyfert 1 galaxies at hard X-rays
  Narrow Line Seyfert 1 (NLSy1) galaxies are a peculiar class of type 1 AGN
(BLSy1). The X-ray properties of individual objects belonging to this class are
often extreme and associated with accretion at high Eddington ratios. Here we
present a study on a sample of 14 NLSy1 galaxies selected at hard X-rays (> 20
keV) from the fourth INTEGRAL/IBIS catalogue. The 20-100 keV IBIS spectra show
hard X-ray photon indeces flatly distributed (Gamma_{20-100 keV} ranging from
~1.3 to ~3.6) with an average value of <Gamma_{20-100 keV}> = 2.3+/-0.7,
compatible with a sample of hard X-ray BLSy1 average slope. Instead, NLSy1 show
steeper spectral indeces with respect to BLSy1 when broad-band spectra are
considered. Indeed, we combine XMM-Newton and Swift/XRT with INTEGRAL/IBIS data
sets to obtain a wide energy spectral coverage (0.3-100 keV). A constraint on
the high energy cut-off and on the reflection component is achieved only in one
source, Swift J2127.4+5654 (E_{cut-off} ~ 50 keV, R=1.0{+0.5}_{-0.4}). Hard
X-ray selected NLSy1 do not display particularly strong soft excess emission,
while absorption fully or partially covering the continuum is often measured as
well as Fe line emission features. Variability is a common trait in this
sample, both at X-ray and at hard X-rays. The fraction of NLSy1 in the hard
X-ray sky is likely to be ~15%, in agreement with estimates derived in
optically selected NLSy1 samples. We confirm the association of NLSy1 with
small black hole masses with a peak at 10^{7} M_{dot} in the distribution,
however hard X-ray NLSy1 seem to occupy the lower tail of the Eddington ratios
distribution of classical NLSy1.
