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

Abstract

We present here broadband radio observations of the CSM interacting SN2019oys. SN2019oys was first detected in the optical and was classified as a Type Ib SN. Then, about $\sim 100$ days after discovery, it showed an optical rebrightening and a spectral transition to a spectrum dominated by strong narrow emission lines, which suggests strong interaction with a distant, dense, CSM shell. We modeled the broadband, multi-epoch, radio spectra, covering 2.2 to 36 GHz and spanning from 22 to 1425 days after optical discovery, as a synchrotron emitting source. Using this modeling we characterized the shockwave and the mass-loss rate of the progenitor. Our broadband radio observations show strong synchrotron emission. This emission, as observed 201 and 221 days after optical discovery, exhibits signs of free-free absorption from the material in front of the shock traveling in the CSM. In addition, the steep power law of the optically thin regime points towards synchrotron cooling of the radiating electrons. Analyzing these spectra in the context of the SN-CSM interaction model gives a shock velocity of 14,000 $\mathrm{km}{\mathrm{s}}^{-1}$, and an electron number density of $2.6\times 10^5\mathrm{c}{\mathrm{m}}^{-3}$ at a distance of $2.6\times 10^{16}$ cm. This translates to a high mass-loss rate from the progenitor massive star of $6.7\times 10^{-4}{\mathrm{M}}_{\odot }\mathrm{y}{\mathrm{r}}^{-1}$ for an assumed wind of 100 $\mathrm{km}{\mathrm{s}}^{-1}$ (assuming constant mass-loss rate in steady winds). The late-time radio spectra, 392 and 557 days after optical discovery, are showing broad spectral peaks. We show that this can be explained by introducing a non-homogeneous CSM structure.

14 pages, 7 figures, 2 tables, submitted to Astronomy & Astrophysics

References in corpus (10)

• Pre-Supernova Evolution of Massive Single and Binary Stars
• The Zwicky Transient Facility: Science Objectives
• The Zwicky Transient Facility: Surveys and Scheduler
• A Wolf-Rayet-like progenitor of supernova SN 2013cu from spectral observations of a wind
• Circumstellar Emission from Type Ib and Ic Supernovae
• Long Term Radio Monitoring of SN 1993J
• The Radio Luminosity-Risetime Function of Core-Collapse Supernovae
• The peculiar mass-loss history of SN 2014C as revealed through AMI radio observations
• Type Ib supernova Master OT J120451.50+265946.6: radio emitting shock with inhomogeneities crossing through a dense shell
• Type IIP supernova SN 2016X in radio frequencies

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