The unusual 2006 dwarf nova outburst of GK Perseii

TL;DR

The 2006 outburst of GK Perseii showed unusual optical and UV behavior with a triple-peaked profile and lower brightness, while X-ray flux remained consistent, revealing complex accretion disc dynamics.

Contribution

This study provides the first broad-band multi-wavelength analysis of GK Perseii's 2006 outburst, highlighting the complex interplay between optical, UV, and X-ray emissions.

Findings

Optical/UV outburst had a triple-peaked morphology with lower peak brightness.

Hard X-ray flux remained consistent with previous outbursts.

Optical/UV profile explained by heating and cooling waves in the accretion disc.

Abstract

The 2006 outburst of GK Perseii differed significantly at optical and ultraviolet wavelengths from typical outbursts of this object. We present multi-wavelength (X-ray, UV and optical) Swift and AAVSO data, giving unprecedented broad-band coverage of the outburst, allowing us to follow the evolution of the longer-than-normal 2006 outburst across these wavelengths. In the optical and UV we see a triple-peaked morphology with maximum brightness ~1.5 magnitudes lower than in previous years. In contrast, the peak hard X-ray flux is the same as in previous outbursts. We resolve this dichotomy by demonstrating that the hard X-ray flux only accounts for a small fraction of the total energy liberated during accretion, and interpret the optical/UV outburst profile as arising from a series of heating and cooling waves traversing the disc, caused by its variable density profile.