GW Librae: Still Hot Eight Years Post-Outburst

TL;DR

Eight years after its outburst, GW Librae's white dwarf remains significantly hotter than quiescent levels, with persistent pulsations indicating it may be nearing its pre-outburst state.

Contribution

This study provides the longest measured cooling timescale for a dwarf nova and documents the persistence of pulsations years after outburst.

Findings

White dwarf remains ~3000 K hotter than quiescent temperature.

Persistent pulsation periods similar to pre-outburst observed.

Long-term cooling timescale established for dwarf nova GW Librae.

Abstract

We report continued Hubble Space Telescope (HST) ultraviolet spectra and ground-based optical photometry and spectroscopy of GW Librae eight years after its largest known dwarf nova outburst in 2007. This represents the longest cooling timescale measured for any dwarf nova. The spectra reveal that the white dwarf still remains about 3000 K hotter than its quiescent value. Both ultraviolet and optical light curves show a short period of 364-373 s, similar to one of the non-radial pulsation periods present for years prior to the outburst, and with a similar large UV/optical amplitude ratio. A large modulation at a period of 2 h (also similar to that observed prior to outburst) is present in the optical data preceding and during the HST observations, but the satellite observation intervals did not cover the peaks of the optical modulation so it is not possible to determine its corresponding UV amplitude. The similarity of the short and long periods to quiescent values implies the pulsating, fast spinning white dwarf in GW Lib may finally be nearing its quiescent configuration.