2021A&A...646A.165S

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 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 1930Å continuum-emitting region. Assuming an accretion disc with an axis inclined at 60° to the line of sight, we obtained log(r_1/2/cm)=15.4_–0.4^+0.93. We also estimated the central black hole mass from spectroscopic data. The width of the CIV, MgII, and Hβ emission lines, and the continuum luminosity at 1350, 3000, and 5100Å, led to log(M_BH/M_☉)=8.6±0.4. Thus, hot gas responsible for the 1930Å continuum emission is likely orbiting a 4.0x10⁸M_☉ black hole at an r_1/2 of only a few tens of Schwarzschild radii.