Active phases and flickering of a symbiotic recurrent nova T CrB

TL;DR

This study investigates the active phases and flickering phenomena in the symbiotic recurrent nova T CrB, revealing that flickering originates from the boundary layer and is linked to variable mass transfer, with active phases occurring roughly every 1000 and 5000 days.

Contribution

It provides new insights into the origin of flickering in T CrB, linking it to the boundary layer and demonstrating its presence in X-ray and optical data, along with characterizing the active phases.

Findings

Flickering is most prominent at harder X-ray energies.

Active phases follow ~1000d and ~5000d periods.

Flickering correlates with flux, originating in the boundary layer.

Abstract

T CrB is a symbiotic recurrent nova known to exhibit active phases, characterised by apparent increases in the hot component temperature and the appearance of flickering, i.e. changes in the observed flux on the time-scale of minutes. Historical UV observations have ruled out orbital variability as an explanation for flickering and instead suggest flickering is caused by variable mass transfer. We have analysed optical and X-ray observations to investigate the nature of the flickering as well as the active phases in T CrB. The spectroscopic and photometric observations confirm that the active phases follow two periods of ~1000d and ~5000d. Flickering in the X-rays is detected and follows an amplitude-flux relationship similar to that observed in the optical. The flickering is most prominent at harder X-ray energies, suggesting that it originates in the boundary layer between the accretion disc and the white dwarf. The X-ray radiation from the boundary layer is then reprocessed by a thick accretion disc or a nebula into UV radiation. A more detailed understanding of flickering would benefit from long-term simultaneous X-ray and optical monitoring of the phenomena in symbiotic recurrent novae and related systems such as Z And type symbiotic stars.