Astrophys. J., 938, 84 (2022/October-2)
Radio Analysis of SN2004C Reveals an Unusual CSM Density Profile as a Harbinger of Core Collapse.
DEMARCHI L., MARGUTTI R., DITTMAN J., BRUNTHALER A., MILISAVLJEVIC D., BIETENHOLZ M.F., STAUFFER C., BRETHAUER D., COPPEJANS D., AUCHETTL K., ALEXANDER K.D., KILPATRICK C.D., BRIGHT J.S., KELLEY L.Z., STROH M.C. and JACOBSON-GALAN W.V.
Abstract (from CDS):
We present extensive multifrequency Karl G. Jansky Very Large Array (VLA) and Very Long Baseline Array (VLBA) observations of the radio-bright supernova (SN) IIb SN 2004C that span ∼40-2793 days post-explosion. We interpret the temporal evolution of the radio spectral energy distribution in the context of synchrotron self-absorbed emission from the explosion's forward shock as it expands in the circumstellar medium (CSM) previously sculpted by the mass-loss history of the stellar progenitor. VLBA observations and modeling of the VLA data point to a blastwave with average velocity ∼0.06 c that carries an energy of ≈1049 erg. Our modeling further reveals a flat CSM density profile ρCSM ∝ R–0.03±0.22 up to a break radius Rbr ≈ (1.96 ± 0.10) × 1016 cm, with a steep density gradient following ρCSM ∝ R–2.3±0.5 at larger radii. We infer that the flat part of the density profile corresponds to a CSM shell with mass ∼0.021 M☉, and that the progenitor's effective mass-loss rate varied with time over the range (50-500) × 10–5M☉ yr–1 for an adopted wind velocity vw = 1000 km s–1 and shock microphysical parameters ϵe = 0.1, ϵB = 0.01. These results add to the mounting observational evidence for departures from the traditional single-wind mass-loss scenarios in evolved, massive stars in the centuries leading up to core collapse. Potentially viable scenarios include mass loss powered by gravity waves and/or interaction with a binary companion.
© 2022. The Author(s). Published by the American Astronomical Society.
Core-collapse supernovae - Stellar mass loss - Circumstellar shells - Circumstellar matter - Supernovae - Radio astronomy
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