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We present here broadband radio observations of the CSM interactingSN2019oys. SN2019oys was first detected in the optical and was classified as aType Ib SN. Then, about $\sim 100$ days after discovery, it showed an opticalrebrightening and a spectral transition to a spectrum dominated by strongnarrow emission lines, which suggests strong interaction with a distant, dense,CSM shell. We modeled the broadband, multi-epoch, radio spectra, covering 2.2to 36 GHz and spanning from 22 to 1425 days after optical discovery, as asynchrotron emitting source. Using this modeling we characterized the shockwaveand the mass-loss rate of the progenitor. Our broadband radio observations showstrong synchrotron emission. This emission, as observed 201 and 221 days afteroptical discovery, exhibits signs of free-free absorption from the material infront of the shock traveling in the CSM. In addition, the steep power law ofthe optically thin regime points towards synchrotron cooling of the radiatingelectrons. Analyzing these spectra in the context of the SN-CSM interactionmodel gives a shock velocity of 14,000 $\rm km \, s^{-1}$, and an electronnumber density of $2.6 \times 10^5 \, \rm cm^{-3}$ at a distance of $2.6 \times10^{16}$ cm. This translates to a high mass-loss rate from the progenitormassive star of $6.7 \times 10^{-4} \, \rm M_{\odot} yr^{-1}$ for an assumedwind of 100 $\rm km s^{-1}$ (assuming constant mass-loss rate in steady winds).The late-time radio spectra, 392 and 557 days after optical discovery, areshowing broad spectral peaks. We show that this can be explained by introducinga non-homogeneous CSM structure.

The dense and non-homogeneous circumstellar medium revealed in radio wavelengths around the Type Ib SN 2019oys