Possible Detection of Very Soft X-Rays from SS Cygni

Rappaport, S.; Cash, Webster; Doxsey, R.; McClintock, J. E.; Moore, G. K. G.

doi:10.1086/181378

Cited by 48 publications

(18 citation statements)

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“…Soft X-rays have been detected during outbursts of SS Cyg (e.g., Rappaport et al 1974;Mason et al 1978;Córdova et al 1980b;Jones & Watson 1992;Ponman et al 1995), U Gem (e.g., ), VW Hyi (van der Woerd et al 1986Mauche et al 1991;van Teeseling et al 1993;Wheatley et al 1996b), SW UMa (Szkody et al 1988), and Z Cam (Wheatley et al 1996a). Other high-Ṁ CVs generally do not show the soft component (e.g., Silber et al 1994;van Teeseling et al 1995).…”

Section: Outbursting Dwarf Novae and Other High-ṁ Cvsmentioning

confidence: 99%

X-rays from cataclysmic variables

Kuulkers

Norton

Schwope

et al. 2006

Compact Stellar X-Ray Sources

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IntroductionCataclysmic Variables * (CVs) are a distinct class of interacting binaries, transferring mass from a donor star to a degenerate accretor, a white dwarf (WD). In all observational determinations, and as is required by theory for stable mass transfer, the donor star is of lower mass than the accretor.The majority of CVs have orbital periods, P orb , between 75 min and 8 h (see Ritter & Kolb 2003) and consist of Roche Lobe-filling main sequence donors and WDs. These are WD analogues of the low-mass X-ray binaries (LMXBs; see Chapter 1). In the period range 8 h-3 d the donors must have larger radii than dwarfs in order to fill their Roche Lobes and are therefore evolved subgiants. A few CVs are found with P orb ∼200 d, which require giant donors for them to be Lobe-filling. The absence of evolved CVs with periods ∼3 to ∼200 d is connected with the dynamical instability that results from an initial donor that had a mass larger than about 67% of that of the WD; such binaries will have experienced rapid mass transfer and shortened their periods during a common envelope phase. Beyond P orb ∼200 d, mass-transferring systems also exist. These constitute the symbiotic binaries (SBs) and are in general not Roche Lobe-filling, but instead consist of a WD orbiting in the wind of a supergiant, and are thus analogues of the high-mass X-ray binaries (see Chapter 1).At the short end of the period range a different kind of CV exists, i.e., in which the mass losing donors are themselves WDs; they are entirely deficient in hydrogen. These helium-transferring CVs are known, after the type star, as AM CVn stars and are observed to have P orb from 60 min down to at least as short as 10 min. They have evolved by passage through two common envelope phases, which leaves the cores of both of the component stars exposed.The CVs are divided into subtypes. These were originally based entirely on the behaviour seen in long-term optical light curves, but to this are now added more subtle parameters such as the presence of polarisation. In essence, a CV's gross behaviour is determined by the rate of mass transfer from the donor,Ṁ donor , and * See Hack & La Dous (1993) and Warner (1995) for comprehensive overviews.

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Section: Outbursting Dwarf Novae and Other High-ṁ Cvsmentioning

confidence: 99%

X-rays from cataclysmic variables

Kuulkers

Norton

Schwope

et al. 2006

Compact Stellar X-Ray Sources

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“…SS Cygni was first detected in X-rays by Rappaport et al (1974). The main site of X-ray emission in DNs is believed to be the boundary layer between the white dwarf and the accretion disk.…”

Section: Introductionmentioning

confidence: 99%

On the Correlated X‐Ray and Optical Evolution of SS Cygni

McGowan

Priedhorsky

Trudolyubov

2004

ApJ

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We have analyzed the variability and spectral evolution of the prototype dwarf nova system SS Cygni using RXTE data and AAVSO observations. A series of pointed RXTE/PCA observations allow us to trace the evolution of the X-ray spectrum of SS Cygni in unprecedented detail, while 6 years of optical AAVSO and RXTE/ASM light curves show long-term patterns. Employing a technique in which we stack the X-ray flux over multiple outbursts, phased according to the optical light curve, we investigate the outburst morphology. We find that the 3-12 keV X-ray flux is suppressed during optical outbursts, a behavior seen previously but only in a handful of cycles. The several outbursts of SS Cygni observed with the more sensitive RXTE/PCA also show a depression of the X-rays during optical outburst. We quantify the time lags between the optical and X-ray outbursts and the timescales of the X-ray recovery from outburst. The optical light curve of SS Cygni exhibits brief anomalous outbursts. During these events the hard X-rays and optical flux increase together. The long-term data suggest that the X-rays decline between outbursts. Our results are in general agreement with modified disk instability models, which invoke a two-component accretion flow consisting of a cool optically thick accretion disk truncated at an inner radius, and a quasi-spherical hot corona-like flow extending to the surface of the white dwarf. We discuss our results in the framework of one such model, involving the evaporation of the inner part of the optically thick accretion disk, proposed by Meyer & Meyer-Hofmeister.

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“…SS Cyg was the first dwarf nova to be detected at X-ray wavelengths (Rappaport et al 1974). In quiescence, SS Cyg is a bright soft X-ray source; hard X-ray emission is generally suppressed, in basic agreement with the standard model (Jones k Watson 1992), though not necessarily absent (Nousek et al 1994).…”

Section: Ss Cygnimentioning

confidence: 66%

The EUVE Observations of Dwarf Novae

Long

1996

International Astronomical Union Colloquium

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In the standard theory of dwarf novae in outburst, the boundary layer region between the inner edge of the accretion disk and the white dwarf surface radiates primarily in the extreme ultraviolet. Using EUVE, observers have been able to obtain spectra with sufficient spectral resolution to characterize accurately the emission from several dwarf novae in outburst, including U Getninorum and SS Cygni. I present an overview of the observations and early analyses of the dwarf nova observations. The spectra obtained of dwarf novae are complex compared to the EUV spectra of magnetic cataclysmic variables and single white dwarfs. Detailed spectral modeling of an expanding atmosphere will most like be required to fully understand the spectra. Nevertheless, we already know there were significant differences in the effective temperatures and other properties of the EUV emissions. If we assume the EUV emission arises primarily from the boundary layer and parameterize the EUV spectrum in terms of a blackbody, then for U Gem the derived boundary luminosity is comparable to the disk luminosity, consistent with the standard theory, and the minimum size of the emitting region is about that of the white dwarf surface. The count rates from U Gem were modulated strongly with the orbital period; differences in the shape of the spectrum in eclipse and out of eclipse suggest that while the bulk of the emission arose from the vicinity of the white dwarf, there was an extended source of emission as well. For SS Cyg, however, the derived boundary layer luminosity was a small fraction of the disk luminosity. In U Gem, the effective temperature dropped during the decline from outburst. In contrast, in SS Cyg, the effective temperature remained constant as the count rate rose by a factor of 100 and the effective size increased. Thus while the observations of U Gem seem broadly consistent with the standard theory for the boundary layer emission from dwarf novae, SS Cyg appears to present fundamental challenges to that theory.

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Possible Detection of Very Soft X-Rays from SS Cygni

Cited by 48 publications

References 0 publications

X-rays from cataclysmic variables

X-rays from cataclysmic variables

On the Correlated X‐Ray and Optical Evolution of SS Cygni

The EUVE Observations of Dwarf Novae

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