Open AccessThe X‐ray and extreme‐ultraviolet flux evolution of SS Cygni throughout outburst
Author(s) -
Wheatley Peter J.,
Mauche Christopher W.,
Mattei Janet A.
Publication year - 2003
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1046/j.1365-8711.2003.06936.x
Subject(s) - physics , astrophysics , white dwarf , extreme ultraviolet , flux (metallurgy) , dwarf nova , ultraviolet , accretion (finance) , astronomy , stars , optics , laser , materials science , metallurgy
We present the most complete multiwavelength coverage of any dwarf nova outburst: simultaneous optical, Extreme Ultraviolet Explorer and Rossi X‐ray Timing Explorer observations of SS Cygni throughout a narrow asymmetric outburst. Our data show that the high‐energy outburst begins in the X‐ray waveband 0.9–1.4 d after the beginning of the optical rise and 0.6 d before the extreme‐ultraviolet rise. The X‐ray flux drops suddenly, immediately before the extreme‐ultraviolet flux rise, supporting the view that both components arise in the boundary layer between the accretion disc and white dwarf surface. The early rise of the X‐ray flux shows that the propagation time of the outburst heating wave may have been previously overestimated. The transitions between X‐ray and extreme‐ultraviolet dominated emission are accompanied by intense variability in the X‐ray flux, with time‐scales of minutes. As detailed by Mauche & Robinson, dwarf nova oscillations are detected throughout the extreme‐ultraviolet outburst, but we find they are absent from the X‐ray light curve. X‐ray and extreme‐ultraviolet luminosities imply accretion rates of 3 × 10 15 g s −1 in quiescence, 1 × 10 16 g s −1 when the boundary layer becomes optically thick, and ∼10 18 g s −1 at the peak of the outburst. The quiescent accretion rate is two and a half orders of magnitude higher than predicted by the standard disc instability model, and we suggest this may be because the inner accretion disc in SS Cyg is in a permanent outburst state.