Resolving the inner accretion flow towards the central supermassive
  black hole in SDSS J1339+1310
  We studied the accretion disc structure in the doubly imaged lensed quasar
SDSS J1339+1310 using $r$-band light curves and UV-visible to near-IR (NIR)
spectra from the first 11 observational seasons after its discovery. The
2009$-$2019 light curves displayed pronounced microlensing variations on
different timescales, and this microlensing signal permitted us to constrain
the half-light radius of the 1930 \r{A} continuum-emitting region. Assuming an
accretion disc with an axis inclined at 60 deg to the line of sight, we
obtained log$_{10}$($r_{1/2}$/cm) = 15.4$^{+0.3}_{-0.4}$. We also estimated the
central black hole mass from spectroscopic data. The width of the Civ, Mgii,
and H$\beta$ emission lines, and the continuum luminosity at 1350, 3000, and
5100 \r{A}, led to log$_{10}$($M_{BH}$/M$_{\odot}$) = 8.6 $\pm$ 0.4. Thus, hot
gas responsible for the 1930 \r{A} continuum emission is likely orbiting a 4.0
$\times$ 10$^8$ M$_{\odot}$ black hole at an $r_{1/2}$ of only a few tens of
Schwarzschild radii.
