The time-dependent rebrightenings in classical novae outbursts: a late-time episodic fuel burning?

TL;DR

This paper analyzes the timing and pattern of rebrightenings in classical novae, revealing they occur as isolated flares with increasing intervals, likely caused by envelope hydrogen burning instabilities, and correlating with nova speed class.

Contribution

It identifies a geometric series pattern in rebrightening intervals and links these to hydrogen burning instabilities, providing new insights into nova outburst behaviors.

Findings

Rebrightenings are isolated flare-like events on smooth light curves.

Intervals between rebrightenings increase as a geometric series.

Slower novae show faster increases in rebrightening intervals.

Abstract

A significant fraction of novae exhibit a series of rebrightenings on the decline branch of their light curves. We use visual observations to study this phase in several well-observed novae. We find that these rebrightenings are isolated flare-like events on otherwise smooth light curves and we show that in most novae in our sample the time intervals between consecutive flares gradually increase as a geometric series; rebrightenings are equally spaced in logarithmic time. We also find a correlation between the rate of increase in the time between rebrightenings with the speed class of the nova in the sense that slower novae tend to increase the time intervals faster. We attribute these rebrightenings to instabilities in the envelope hydrogen burning and we mention other cases of such timing pattern in astronomy and natural sciences in general.