Swift observations of GW Lib: a unique insight into a rare outburst

TL;DR

This paper presents multiwavelength observations of the rare 2007 outburst of GW Lib, revealing unusual X-ray behavior and long quiescent periods, providing new insights into the accretion processes of WZ Sge type dwarf novae.

Contribution

It offers the first detailed multiwavelength data of GW Lib's outburst, highlighting its unique X-ray properties and long interoutburst timescale, advancing understanding of dwarf nova accretion dynamics.

Findings

X-ray flux increased by three orders of magnitude at optical maximum

Detection of a supersoft X-ray component likely from an optically-thick boundary layer

Post-outburst X-ray flux remains elevated a year after the outburst

Abstract

The second known outburst of the WZ Sge type dwarf nova GW Lib was observed in April 2007. We have obtained unique multiwavelength data of this outburst which lasted ~ 26 days. AAVSO observers recorded the outburst in the optical, which was also monitored by WASP, with a peak V magnitude of ~ 8. The outburst was followed in the UV and X-ray wavelengths by the Swift UVOT and XRT telescopes. The X-ray flux at optical maximum was found to be three orders of magnitude above the pre-outburst quiescent level, whereas X-rays are normally suppressed during dwarf nova outbursts. A distinct supersoft X-ray component was also detected at optical maximum, which probably arises from an optically-thick boundary layer. Follow-up Swift observations taken one and two years after the outburst show that the post-outburst quiescent X-ray flux remains an order of magnitude higher than the pre-outburst flux. The long interoutburst timescale of GW Lib with no observed normal outbursts support the idea that the inner disc in GW Lib is evacuated or the disc viscosity is very low.