Radio and X-Ray Observations of the Transitional Supernova 2019yvr: Insights into the Progenitor Mass-loss History

The final life stages of the massive star progenitors of stripped-envelope supernovae (SESNe) remain an open question, especially when it comes to the timing and magnitude of the progenitor stripping. Observing SESNe across the electromagnetic spectrum allows for the most direct constraints on mass loss in the final stages of progenitor evolution. In this work, we present radio (GMRT+VLA) and X-ray (Swift+Chandra) observations of SN 2019yvr obtained from 18 to 1784 days postexplosion. SN 2019yvr was a Type Ib supernova (SN Ib, with strong helium but little or no hydrogen ) that transitioned into a Type IIn supernova (SN IIn, with shock-driven hydrogen features from interaction with circumstellar material, CSM) at ∼100 days postexplosion. The radio evolution is best fit by a synchrotron self-absorbed model with a ρ ∝ r −1.54±0.31 CSM density profile, suggesting a decreasing mass-loss rate from the progenitor in the years leading up to the explosion. The radio-derived shock speed is high, more than 30,000 km s −1 at early times, suggesting a compact progenitor star. The combined radio and X-ray data probe CSM that extends from 1.7 × 10 16 cm up to ∼20 × 10 16 cm and was created by mass loss from ∼(1−3) × 10 −5 M ⊙ yr −1 (assuming a CSM speed of 100 km s −1 ). The combined dataset rules out any dramatic jump in CSM density (which was seen in the optical analog SN 2014C) associated with the emergence of optical hydrogen emission lines. We place SN 2019yvr in context with similar transitional SNe and discuss implications for the progenitor.