Multi-wavelength study of the pre-eruption dip in the recurrent nova T Coronae Borealis preceding imminent nova eruption

TL;DR

This multi-wavelength study of T Coronae Borealis reveals pre-eruption dips characterized by anti-correlated UV/X-ray fluxes and increasing brightness amplitudes at shorter wavelengths, indicating accretion rate changes that may signal an imminent nova eruption.

Contribution

It provides the first detailed multi-wavelength analysis of pre-eruption dips in T CrB, linking flux variability to accretion dynamics and eruption prediction.

Findings

UV and X-ray fluxes are anti-correlated during the dip phases.

A second, lower-amplitude dip was observed after the primary dip.

Flux variations support an accretion-variation scenario as a precursor to eruption.

Abstract

We present a multi-wavelength study of the symbiotic recurrent nova (RN) T Coronae Borealis (T CrB) using Swift Burst Alert Telescope (BAT) / X-Ray Telescope (XRT) / UltraViolet Optical Telescope (UVOT) and American Association of Variable Stars Observers (AAVSO) observations from 2005 to 2025. Our analysis spans quiescent, high, and pre-eruption dip states. We find that brightening amplitudes increase toward shorter wavelengths in both optical and UV bands, while the UV and X-ray fluxes are generally anti-correlated throughout all phases. During the 2023-2024 pre-eruption dip, soft and hard X-rays increased as optical and ultraviolet (UV) brightness declined, consistent with a transition from an optically thick to thin boundary layer driven by a reduction in the accretion rate. We also report, for the first time, a second, lower-amplitude dip occurring between September 2024 and February 2025 following the primary 2023-2024 pre-eruption dip. The observed variability supports an accretion-variation scenario as a unifying explanation for both the high and dip states, and may signal an imminent nova eruption.