The activity of the post-nova V1363 Cyg on long timescales

TL;DR

This study analyzes long-term optical data of the post-nova V1363 Cyg, revealing its accretion disk's thermal-viscous instability, variable outburst behavior, and a persistent 435-day cycle likely linked to the companion's mass outflow modulation.

Contribution

It provides the first detailed long-term analysis of V1363 Cyg's activity, highlighting its disk instability behavior and the potential for an unusually long orbital period.

Findings

Accretion disk exhibits thermal-viscous instability over decades.

Brightness variations include episodes of strong brightening from a cool disk.

A persistent 435-day cycle suggests modulation of mass outflow from the companion.

Abstract

V1363 Cyg is a cataclysmic variable (CV) and a post-nova. Our analysis of its long-term optical activity used the archival data from the AAVSO database and literature. We showed that the accretion disk of V1363 Cyg is exposed to the thermal-viscous instability (TVI) for at least part of the time. The time fraction spent in the high state or the outbursts dramatically changed on the timescale of decades. Highly variable brightness of V1363 Cyg displayed several episodes of a strong brightening (bumps in the light curve) from a cool disk in the TVI zone. In the interpretation, their vastly discrepant decay rates show that only some of these bumps can be attributed to the dwarf nova outbursts without strong irradiation of the disk by the hot white dwarf. The Bailey relation of the decay rate, if ascribed to a DN outburst of V1363 Cyg, speaks in favor of its orbital period $P_{\rm orb}$ very long for a CV, about 20-40 hr. A dominant cycle length of about 435 d was present in the brightness changes all the time, even when the disk was well inside the TVI zone. We interpret it as modulation of the companion's mass outflow by differential rotation of the active region(s).