Speaker
Description
We present preliminary results from our on-going NOT programme
"Changing State QSO's: a clue to understand their physics".
Extreme photometric variations in
AGN's are often accompanied by large spectral changes whose origin
is not yet understood. This includes Changing Look or Changing State Quasars
(changes in the BLR), candidate Tidal Disruption Events, Erratic Blazar
Variability. Spectral analysis of more cases with large
photometric changes, is necessary to disentangle the role of
reddening variations, changes in the structure of the BLR or
variations in the accretion rate, among others.
The Gaia Alerts provide an all-sky photometric transient survey,
based on the repeated, high-precision measurements made by the Gaia satellite.
Our spectroscopic data suggest that in many cases about one magnitude
long term out burst is associated with a significant spectral change,
such as changing from LINER to Seyfert 1 or strong change in Balmer lines.
The time scales of the spectral changes after the initial change appear
to be rather slow from months to years.
As many objects were detected in the raising phase, those should
be monitored particularly to detect their possible decreasing again and the
associated spectral changes.
In addition, we have been monitoring rare Fast Rise and
Exponential decay (FRED) events among others.
