Long-term variability of the composite galaxy SDSS J103911-000057: A
  candidate of true Type-2 AGN
  In the manuscript, the composite galaxy SDSS J103911-000057 (=SDSS J1039) is
reported as a better candidate of true Type-2 AGN without hidden BLRs. None
broad but only narrow emission lines detected in SDSS J1039 can be well
confirmed both by the F-test technique and by the expected broad emission lines
with EW smaller than 13.5\AA~ with 99\% confidence level. Meanwhile, a reliable
AGN power law component is preferred with confidence level higher than 7sigma
in SDSS J1039. Furthermore, the long-term variability of SDSS J1039 from CSS
can be well described by the DRW process with intrinsic variability timescale
$\tau\sim100{\rm days}$, similar as normal quasars. And, based on BH mass in
SDSS J1039 through the msig relation and on the correlation between AGN
continuum luminosity and total H$\alpha$ luminosity, the expected broad
H$\alpha$, if there was, could be re-constructed with line width about
$300-1000{\rm km~s^{-1}}$ and with line flux about $666\times10^{-17}{\rm
erg~s^{-1}~cm^{-2}}$ under the Virialization assumption to BLRs, providing
robust evidence to reject the probability that the intrinsic probable broad
H$\alpha$ were overwhelmed by noises of the SDSS spectrum in SDSS J1039.
Moreover, the SDSS J1039 does follow the same correlation between continuum
luminosity and [O~{\sc iii}] line luminosity as the one for normal broad line
AGN, indicating SDSS J1039 classified as a changing-look AGN at dim state can
be well ruled out. Therefore, under the current knowledge, SDSS J1039 is a
better candidate of true Type-2 AGN.
