Confirmation of intermediate-mass black holes candidates with X-ray
  observations
  The origin of supermassive black holes (SMBH) in galaxy centers still remains
uncertain. There are two possible ways of their formation - from massive ($10^5
- 10^6 M_{\odot}$) and low-mass ($100 M_{\odot}$) BH nuclei. The latter
scenario should leave behind a large number of intermediate mass black holes
(IMBH, $10^2 - 10^5 M_{\odot}$). The largest published sample of bona-fide
IMBH-powered AGN contains 10 objects confirmed in X-ray. Here we present a new
sample of 15 bona-fide IMBHs, obtained by confirming the optically selected
IMBH candidates by the presence of radiation from the galactic nucleus in the
X-ray range, which increases the number of confirmed IMBHs at the centers of
galaxies by 2.5 times. In the same way, 99 black holes with masses of
$2\cdot10^5 - 10^6 M_{\odot}$ were confirmed. The sources of X-ray data were
publicly available catalogs, archives of data, and our own observations on
XMM-Newton, Chandra and Swift. The Eddington coefficients for 30% of the
objects from both samples turned out to be close to critical, from 0.5 to 1,
which is an unusually high fraction. Also for the first time for light-weight
SMBH the correlations between the luminosity in the [OIII] emission line or the
broad component of the $H\alpha$ line and the luminosity in the X-ray range
were plotted.
