Hourly radio variability of PD,70c from time-differential photometry

The radio emission mechanisms from accreting protoplanets and their variability link observations and physical properties. We revisit the variability of the ∼343,GHz (ALMA Band 7) flux density from PDS,70c (F_ B7). The subtraction of the extended time-averaged signal may enable the measurement of the flux density from variable and embedded point sources. Visibility alignment and self-calibration yield close to thermal residuals in each execution block (EB) of ALMA observations, thus allowing the time-differential photometry of point-sources in the visibility domain. The variability of PDS,70c was checked against synthetic control point sources. In images of the 2017 ALMA dataset, with three ∼1,h EBs, PDS,70c was detected only on 6 December 2017, where F_ B7 rose by 228% (3.3σ). Time-differential photometry confirms a rise by 170% (t) shows some scatter when splitting the deep 2023 EBs into 20,min intervals, with a ̧hi^2 test significant at 2.6,σ, and an intrinsic dispersion of 49% (3.7σ). An application to ∼2,h EBs from the 2023 dataset resulted in constant flux densities, within a scatter of ∼15%. However, F_ ̊m B7 The radio variability of PDS,70c, observed over hours but averaged out on longer timescales, is indeed expected if the signal is due to i free-free from an accretion shock on a circumplanetary disk surface. A planet-to-environment mass ratio <10^-4 is required to avoid smoothing by radiative diffusion if the signal is due to thermal emission from the environment.