Evidence for a circumplanetary disc around protoplanet PDS 70 b

We present the first observational evidence for a circumplanetary disc around the protoplanet PDS 70b, based on a new spectrum in the $K$ band acquired with VLT/SINFONI. We tested three hypotheses to explain the spectrum: Atmospheric emission from the planet with either (1) a single value of extinction or (2) variable extinction, and (3) a combined atmospheric and circumplanetary disc model. Goodness-of-fit indicators favour the third option suggesting circumplanetary material contributing excess thermal emission --- most prominent at $2.3 \mu$m. Inferred accretion rates ($ 10^-7.8$--$10^-7.3 M_J$ yr$^-1$) are compatible with observational constraints based on the H$\alpha$ and Br$\gamma$ lines. For the planet, we derive an effective temperature of 1500--1600 K, surface gravity $\log(g) 4.0$, radius $ 1.6 R_J$, mass $ 10 M_J$ and possible thick clouds. Models with variable extinction lead to slightly worse fits. However, the amplitude ($\Delta A_V 3$mag) and timescale of variation ($\lesssim$ years) required for the extinction would also suggest circumplanetary material.