Discovery of a New WZ Sagittae Type Cataclysmic Variable in the Kepler/K2 Data

TL;DR

This paper reports the discovery of a new WZ Sagittae type dwarf nova in Kepler/K2 data, providing detailed analysis of its outburst behavior, superhump periods, and rebrightening phase, highlighting its uniqueness and contributing to understanding of such systems.

Contribution

First detection of a WZ Sagittae type system during an outburst in Kepler/K2 data, with detailed light curve analysis and comparison to SU UMa stars.

Findings

Identified a new WZ Sge-type dwarf nova with characteristic superhumps.

Observed an unusual rebrightening phase indicating a type-A outburst.

Demonstrated a common linear rise in superoutbursts of SU UMa stars.

Abstract

We identify a new, bright transient in the Kepler/K2 Campaign 11 field. Its light curve rises over seven magnitudes in a day and then declines three magnitudes over a month before quickly fading another two magnitudes. The transient was still detectable at the end of the campaign. The light curve is consistent with a WZ~Sge type dwarf nova outburst. Early superhumps with a period of 82 minutes are seen in the first 10 days and suggest that this is the orbital period of the binary which is typical for the WZ~Sge class. Strong superhump oscillations develop ten days after peak brightness with periods ranging between 83 and 84 minutes. At 25 days after the peak brightness a bump in the light curve appears to signal a subtle rebrightening phase implying that this was an unusual type-A outburst. This is the only WZ~Sge type system observed by Kepler/K2 during an outburst. The early rise of this outburst is well-fit with a broken power law. In first 10 hours the system brightened linearly and then transitioned to a steep rise with a power law index of 4.8. Looking at archival Kepler/K2 data and new TESS observations, a linear rise in the first several hours at the initiation of a superoutburst appears to be common in SU~UMa stars.