A flare in the optical spotted in the changing-look Seyfert NGC 3516
  We present observations from the short-term intensive optical campaign (from
Sep2019 to Jan2020) of the changing-look Seyfert NGC 3516. This active galactic
nucleus is known to have strong optical variability and has changed its type in
the past. It has been in the low-activity state in the optical since 2013, with
some rebrightening from the end of 2015 to the beginning of 2016, after which
it remained dormant. We aim to study the photometric and spectral variability
of NGC 3516 from the new observations in U- and B-bands and examine the
profiles of the optical broad emission lines in order to demonstrate that this
object may be entering a new state of activity. NGC 3516 has been monitored
intensively for the past 4 months with an automated telescope in U and B
filters, enabling accurate photometry of 0.01 precision. Spectral observations
were triggered when an increase in brightness was spotted. We support our
analysis of past-episodes of violent variability with the UV and X-ray
long-term light curves constructed from the archival Swift data. An increase of
the photometric magnitude is seen in both U and B filters to a maximum
amplitude of 0.25mag and 0.1 mag, respectively. During the flare, we observe
stronger forbidden high-ionization iron lines than reported before, as well as
the complex broad Ha and Hb lines. This is especially seen in Ha which appears
to be double-peaked. It seems that a very broad component of ~10,000 km/s in
width in the Balmer lines is appearing. The trends in the optical, UV, and
X-ray light curves are similar, with the amplitudes of variability being
significantly larger in the case of UV and X-ray bands. The increase of the
continuum emission, the variability of the coronal lines, and the very broad
component in the Balmer lines may indicate that the AGN of NGC 3516 is finally
leaving the low-activity state in which it has been for the last ~3 years.
