The pre-eruption state of T CrB as observed with ALMA in 2024

Abstract

T CrB is a nearby symbiotic binary and a recurrent nova with a period of ca. 80 years. The next eruption is expected to take place in 2025 or 2026. We present our pre-eruption observations made in ALMA frequency Bands 1, 3, 4, 6, 7, and 8 in August to November 2024 and constrain the properties of the environment into which the imminent next nova will erupt. We find that in the second half of 2024, the quiescent T CrB was a faint mm source with a spectral energy distribution well described by a powerlaw with index $\alpha =$0.56$\pm$0.11 and a flux density of ca. 0.1 mJy at 44 GHz and 0.4 mJy at 400 GHz. There is no significant line emission. This is in agreement with expectations for free-free emission from the partially ionized wind of the red giant donor star and, in extrapolation to 35 GHz, a factor 5 fainter than the emission observed in 2016/17 during the latest high state. Comparing the spectra from that high-state between 13.5 GHz and 35 GHz with our spectrum from 2024, our spectrum is softer. The spectral index is on average lower by 0.34$\pm$0.11 . Our per-band and aggregate bandwidth images of T CrB show an unresolved point source with no evidence for extended structure. A simple model of a free-free emitting, fully-ionized stellar wind seems to describe well the 2016/17 high state of T CrB but not our 2024 ALMA measurements with their low flux and high turnover frequency suggesting that in 2024, the wind was far from fully ionized. (See the unabridged version of the abstract in the paper.)

9 pages, accepted by A&A

References in corpus (16)

• Estimating distances from parallaxes. V: Geometric and photogeometric distances to 1.47 billion stars in Gaia Early Data Release 3
• CASA, the Common Astronomy Software Applications for Radio Astronomy
• X-Ray Emitting Blast Wave from the Recurrent Nova RS Ophiuchi
• An asymmetric shock wave in the 2006 outburst of the recurrent nova RS Ophiuchi
• 3D simulations of RS Oph: from accretion to nova blast
• Accurate determination of the free-free Gaunt factor; I - non-relativistic Gaunt factors
• An Expanding Shell and Synchrotron Jet in RS Ophiuchi
• The ALMA Interferometric Pipeline Heuristics
• Proton acceleration in thermonuclear nova explosions revealed by gamma rays
• Three-dimensional modeling of the asymmetric blast wave from the 2006 outburst of RS Ophiuchi: Early X-ray emission
• The B & V Light Curves for Recurrent Nova T CrB From 1842--2022, the Unique Pre- and Post-Eruption High-States, the Complex Period Changes, and the Upcoming Eruption in 2025.5$\pm$1.3
• Radio interferometric imaging of RS Oph bipolar ejecta for the 2021 nova outburst
• Resolving the mass transfer in the symbiotic recurrent nova T Coronae Borealis
• T CrB: Radio Observations During the 2016--2017 "Super-Active" State
• Multiwavelength spectroscopic study of shock driven phenomena in explosive outbursts in symbiotic-like recurrent novae with emphasis on RS Ophiuchi
• Low-frequency radio observations of recurrent nova RS Ophiuchi with MeerKAT and LOFAR

Cited by in corpus (1)

• High-energy Neutrino Predictions for T Coronae Borealis: Probing Particle Acceleration in Novae