Broad-line region structure and line profile variations in the changing
  look AGN HE1136-2304
  A strong X-ray outburst was detected in HE1136-2304 in 2014. Accompanying
optical spectra revealed that the spectral type has changed from a nearly
Seyfert 2 type (1.95), classified by spectra taken 10 and 20 years ago, to a
Seyfert 1.5 in our most recent observations. We seek to investigate a detailed
spectroscopic campaign on the spectroscopic properties and spectral variability
behavior of this changing look AGN and compare this to other variable Seyfert
galaxies. We carried out a detailed spectroscopic variability campaign of
HE1136-2304 with the 10 m Southern African Large Telescope (SALT) between 2014
December and 2015 July. The broad-line region (BLR) of HE1136-2304 is
stratified with respect to the distance of the line-emitting regions. The
integrated emission line intensities of Halpha, Hbeta, HeI 5876, and HeII 4686
originate at distances of 15.0 (+4.2,-3.8), 7.5 (+4.6,-5.7), 7.3 (+2.8,-4.4),
and 3.0 (+5.3,-3.7) light days with respect to the optical continuum at 4570AA.
The variability amplitudes of the integrated emission lines are a function of
distance to the ionizing continuum source as well. We derived a central black
hole mass of 3.8 (+-3.1) 10exp(7) M_solar based on the line widths and
distances of the BLR. The outer line wings of all BLR lines respond much faster
to continuum variations indicating a Keplerian disk component for the BLR. The
response in the outer wings is about two light days shorter than the response
of the adjacent continuum flux with respect to the ionizing continuum flux. The
vertical BLR structure in HE1136-2304 confirms a general trend that the
emission lines of narrow line active galactic nuclei (AGNs) originate at larger
distances from the midplane in comparison to AGNs showing broader emission
lines. Otherwise, the variability behavior of this changing look AGN is similar
to that of other AGN.
