Gravitational Lens System PS J0147+4630 (Andromeda's Parachute): Main
  Lensing Galaxy and Optical Variability of the Quasar Images
  Because follow-up observations of quadruple gravitational lens systems are of
extraordinary importance for astrophysics and cosmology, we present
single-epoch optical spectra and $r$--band light curves of PS J0147+4630. This
recently discovered system mainly consists of four images ABCD of a background
quasar around a foreground galaxy G that acts as a gravitational lens. First,
we use long--slit spectroscopic data in the Gemini Observatory Archive and a
multi-component fitting to accurately resolve the spectra of A, D, and G. The
spectral profile of G resembles that of an early-type galaxy at a redshift of
0.678 $\pm$ 0.001, which is about 20\% higher than the previous estimate.
Additionally, the stellar velocity dispersion is measured to $\sim$5\%
precision. Second, our early $r$-band monitoring with the Liverpool Telescope
leads to accurate light curves of the four quasar images. Adopting time delays
predicted by the lens model, the new lens redshift, and a standard cosmology,
we report the detection of microlensing variations in C and D as large as
$\sim$0.1 mag on timescales of a few hundred days. We also estimate an actual
delay between A and B of a few days (B is leading), which demonstrates the big
potential of optical monitoring campaigns of PS J0147+4630.
