The "super-active" accretion phase of T CrB has ended

TL;DR

The paper documents the end of a super-active accretion phase in T CrB, marked by increased emission lines and brightness, which has now subsided, indicating the accretion disk has emptied and a new eruption may be imminent.

Contribution

It provides detailed observational evidence of the transition from a super-active accretion phase to quiescence in T CrB, highlighting the end of the 2014-2016 SAP.

Findings

Emission lines and brightness peaked in 2016 and have since returned to pre-SAP levels.

The accretion disk has likely emptied, ending the super-active phase.

The system is poised for a new nova eruption.

Abstract

The symbiotic recurrent nova T CrB erupted for the second and last recorded time in 1946. Following the outburst, the accretion rate onto its WD has remained rather low with only occasional and minor flaring episodes, until in late 2014 it entered a "super-active" phase (SAP) that peaked in April 2016: the flux radiated by Balmer lines increased by two orders of magnitude, accompanied by the appearance of strong HeI, HeII, and many other emission lines. Following the sharp maximum, the intensity of the emission lines has been steadily decreasing, reaching back the pre-SAP levels by mid-2023. The end of SAP is also confirmed by the drop of $B$-band brightness to pre-SAP conditions and the simultaneous re-appearance of a large-amplitude flickering. This suggest that the accretion disk has emptied from the extra material that has driven the "super active" state and has completed its transfer onto the WD, setting the stage for a new and probably imminent nova eruption.