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.
Highlights
Dwarf novae (DNe) are non-magnetic cataclysmic variables (CVs) with accretion discs and a white dwarf primary and a main-sequence secondary star
SU UMa type DNe show superoutbursts which can last for several weeks and are characterized by superhumps, periodic brightenings whose recurrence times are slightly longer than the orbital period
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
Summary
Dwarf novae (DNe) are non-magnetic cataclysmic variables (CVs) with accretion discs and a white dwarf primary and a main-sequence secondary star. This outburst, which was recorded by the AAVSO observers, Wide Angle Search for Planets (WASP)-South and by Swift, lasted for 26 days. Typical characteristics of WZ Sge type stars are short orbital periods, low mass-transfer rates and extremely long recurrence times which can last for decades. The American Association of Variable Star Observers (AAVSO) recorded the outburst in the optical, which was monitored by Wide Angle Search for Planets, with a peak. May 10 onwards were taken at a roll angle which placed a nearby source (TYC6766-1570-1) on a line between our source and in the same direction as the dispersion direction These spectra were severely contaminated and we exclude them from our analysis.
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