Gravitational lens system SDSS J1339+1310: microlensing factory and time
  delay
  We spectroscopically re-observed the gravitational lens system SDSS
J1339+1310 using OSIRIS on the GTC. We also monitored the $r$-band variability
of the two quasar images (A and B) with the LT over 143 epochs in the period
2009$-$2016. These new data in both the wavelength and time domains have
confirmed that the system is an unusual microlensing factory. The
C$\scriptsize{\rm{IV}}$ emission line is remarkably microlensed, since the
microlensing magnification of B relative to that for A, $\mu_{\rm{BA}}$,
reaches a value of 1.4 ($\sim$ 0.4 mag) for its core. Moreover, the B image
shows a red wing enhancement of C$\scriptsize{\rm{IV}}$ flux (relative to A),
and $\mu_{\rm{BA}}$ = 2 (0.75 mag) for the C$\scriptsize{\rm{IV}}$ broad-line
emission. Regarding the nuclear continuum, we find a chromatic behaviour of
$\mu_{\rm{BA}}$, which roughly varies from $\sim$ 5 (1.75 mag) at 7000 \AA\ to
$\sim$ 6 (1.95 mag) at 4000 \AA. We also detect significant microlensing
variability in the $r$ band, and this includes a number of microlensing events
on timescales of 50$-$100 d. Fortunately, the presence of an intrinsic 0.7 mag
dip in the light curves of A and B, permitted us to measure the time delay
between both quasar images. This delay is $\Delta t_{\rm{AB}}$ = 47$^{+5}_{-6}$
d (1$\sigma$ confidence interval; A is leading), in good agreement with
predictions of lens models.
