Non-thermal radio emission in Sakurai's Object

Abstract

The very late thermal pulse (VLTP) affects the evolution of $\sim$20\% of 1--8\,${\mathrm{M}}_{\odot }$ stars, repeating the last phases of the red giant within a few years and leading to the formation of a new, but hydrogen-poor nebula within the old planetary nebula (PN). The strong dust formation in the latter obscures the optical and near-infrared radiation of the star. We aimed to determine the reheating timescale of the central star in Sakurai's object, which is an important constraint for the poorly understood VLTP evolution. We observed the radio continuum emission of Sakurai's object for almost 20 years from 2004 to 2023. Continuous, multi-frequency observations proved to be essential to distinguish between phases dominated by photoionization and shock ionization. The flux density fluctuates by more than a factor 40 within months to years. The spectral index remained negative between 2006 and 2017 and is close to zero since 2019. The emission region is barely resolved since 2021. Non-thermal radio emission observed from 2004 to 2017 traces shocks induced by wind interactions due to discrete mass-loss events. Thermal emission dominates during the period 2019--2023 and may indicate photoionization of the nebula by the central star.

6 pages, 3 figures, 2 tables, Astronomy & Astrophysics, accepted after minor revision

References in corpus (20)

• CASA, the Common Astronomy Software Applications for Radio Astronomy
• The Evolution of Isotope Ratios in the Milky Way Galaxy
• A search for ionized jets towards massive young stellar objects
• The evolutionary time scale of Sakurai's object: A test of convection theory?
• New evolutionary calculations for the Born Again scenario
• The Evolution of NGC 7027 at Radio Frequencies: A New Determination of the Distance and Core Mass
• The onset of photoionization in Sakurai's Object (V4334 Sgr)
• Freshly ionized matter around the final Helium shell flash object V4334 Sgr (Sakurai's object)
• Radio observations of the planetary nebula around the OH/IR Star OH354.88-0.54 (V1018 Sco)
• Time-variable non-thermal emission in the planetary nebula IRAS 15103-5754
• Electron Cooling in a Young Radio Supernova: SN 2012aw
• The inside-out planetary nebula around a born-again star
• Carbon dust in the evolved born-again planetary nebulae A30 and A78
• Radio variability and non-thermal components in stars evolving toward planetary nebulae
• The infrared view of dust and molecules around V4334 Sgr (Sakurai's Object): a 20-year retrospective
• Radio observations of planetary nebulae: no evidence for strong radial density gradients
• A Multi-Epoch Study of Radio Continuum Emission from MassiveProtostars
• WR 72: a born-again planetary nebula with hydrogen-poor knots
• The sub-millimetre evolution of V4334 Sgr (Sakurai's Object)
• V4334 Sgr (Sakurai's Object): still churning out the dust

Cited by in corpus (4)

• A primer on the formation and evolution of hydrogen deficient Central Stars of Planetary Nebulæ and Related Objects
• ASKAP-EMU radio continuum detection of planetary nebula NGC 5189: the "Infinity" nebula
• Long and short term variability of the possible nascent planetary nebula IRAS 22568+6141: A late thermal pulse?
• Magnetic fields in planetary nebulae detected through non-thermal radio continuum emission