Improving Damped Random Walk parameters for SDSS Stripe 82 Quasars with
  Pan-STARRS1
  We use the Panoramic Survey Telescope and Rapid Response System 1 Survey
(Pan-STARRS1, PS1) data to extend the Sloan Digital Sky Survey (SDSS) Stripe 82
quasar light curves. Combining PS1 and SDSS light curves provides a 15 yr
baseline for 9248 quasars - 5 yr longer than prior studies that used only SDSS.
We fit the light curves with the damped random walk (DRW) model model - a
statistical description of their variability. We correlate the resulting DRW
model parameters: asymptotic variability amplitude SF$_{\infty}$, and
characteristic timescale $\tau$, with quasar physical properties - black hole
mass, bolometric luminosity, and redshift. Using simulated light curves, we
find that a longer baseline allows us to better constrain the DRW parameters.
After adding PS1 data, the variability amplitude is a stronger function of the
black hole mass, and has a weaker dependence on quasar luminosity. In addition,
the characteristic timescale $\tau$ dependence on quasar luminosity is
marginally weaker. We also make predictions for the fidelity of DRW model
parameter retrieval when light curves will be further extended with Zwicky
Transient Facility (ZTF) and the Rubin Observatory Legacy Survey of Space and
Time (LSST) data. Finally, we show how updated DRW parameters offer an
independent method of discovering changing-look quasar candidates (CLQSOs). The
candidates are outliers in terms of differences in magnitude and scatter
between SDSS and PS1 segments. We identify 40 objects (35 newly reported) with
tenfold increase in variability timescale between SDSS and SDSS--PS1 data,
which is due to a large change in brightness (over 0.5 mag) - characteristic
for CLQSOs.
