X-ray spectral variations of U Gem from quiescence to outburst

Güver, T.; Uluyazi, C.; Özkan, M. T.; Göǧüş, E.

doi:10.1111/j.1365-2966.2006.10896.x

Cited by 12 publications

(13 citation statements)

References 27 publications

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“…Known exceptions to this general rule are GWLib, which is so X-ray faint in quiescent that this may not be surprising (Byckling et al 2009), and UGem, whose outburst X-ray spectrum is too complex to allow a straightforward measurement of the temperature change (Güver et al 2006). The picture of Patterson & Raymond (1985b), in which an optically thin region exists in the outskirts of an optically thick boundary would not provide a prediction for the luminosity.…”

Section: The Residual Hard X-raysmentioning

confidence: 99%

X-Ray Emissions from Accreting White Dwarfs: A Review

Mukai

2017

PASP

249

212

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Interacting binaries in which a white dwarf accretes material from a companion-cataclysmic variables (CVs) in which the mass donor is a Roche-lobe filling star on or near the main sequence, and symbiotic stars in which the mass donor is a late type giant-are relatively commonplace. They display a wide range of behaviors in the optical, X-rays, and other wavelengths, which still often baffle observers and theorists alike. Here I review the existing body of research on X-ray emissions from these objects for the benefits of both experts and newcomers to the field. I provide introductions to the past and current X-ray observatories, the types of known X-ray emissions from these objects, and the data analysis techniques relevant to this field. I then summarize of our knowledge regarding the X-ray emissions from magnetic CVs, non-magnetic CVs and symbiotic stars, and novae in eruption. I also discuss space density and the X-ray luminosity functions of these binaries and their contribution to the integrated X-ray emission from the Galaxy. I then discuss open questions and future prospects.

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Section: The Residual Hard X-raysmentioning

confidence: 99%

X-Ray Emissions from Accreting White Dwarfs: A Review

Mukai

2017

PASP

249

212

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“…As for WW Cet, we arrive at the same set of answers as for VW Hyi based on the RXTE campaign. As for U Gem, the X-rays are in fact enhanced during outburst (Mattei et al 2000), and the outburst spectral shape is complex enough to preclude a simple answer to the "softening" question (Güver et al 2006). GW Lib is another dwarf nova with a higher X-ray flux during outburst (Byckling et al 2009), which was also harder.…”

Section: Comparisons With Past Campaignsmentioning

confidence: 99%

The Fall and the Rise of X-Rays from Dwarf Novae in Outburst:RXTEObservations of VW Hydri and WW Ceti

Fertig

Mukai

Nelson

et al. 2011

Publications of the Astronomical Society of the Pacific

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In a dwarf nova, the accretion disk around the white dwarf is a source of ultraviolet, optical, and infrared photons, but is never hot enough to emit X-rays. Observed X-rays instead originate from the boundary layer between the disk and the white dwarf. As the disk switches between quiescence and outburst states, the 2-10 keV X-ray flux is usually seen to be anti-correlated with the optical brightness. Here we present RXTE monitoring observations of two dwarf novae, VW Hyi and WW Cet, confirming the optical/X-ray anti-correlation in these two systems. However, we do not detect any episodes of increased hard X-ray flux on the rise (out of two possible chances for WW Cet) or the decline (two for WW Cet and one for VW Hyi) from outburst, attributes that are clearly established in SS Cyg. The addition of these data to the existing literature establishes the fact that the behavior of SS Cyg is the exception, rather than the archetype as is often assumed. We speculate on the origin of the diversity of behaviors exhibited by dwarf novae, focusing on the role played by the white dwarf mass.

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“…In general, the X-ray spectra of nonmagnetic CVs are well modeled with the multitemperature isobaric cooling flow type plasma emission models as in MKCFLOW or CEVMKL (Mukai et al 2003;Baskill et al 2005;Pandel et al 2005;Guver et al 2006;Okada et al 2008;Balman et al 2011;Balman 2014). The X-ray spectra of nonmagnetic CVs show several different emission lines, revealing the existence of hot, optically thin plasma in these systems (see also Balman 2012).…”

Section: Spectral Analysismentioning

confidence: 99%

SWIFTX-RAY TELESCOPE OBSERVATIONS OF THE NOVA-LIKE CATACLYSMIC VARIABLES MV Lyr, BZ Cam, AND V592 Cas

Balman

Godon

Sion

2014

ApJ

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We present a total of ∼45 ks (3 × 15 ks) of Swift X-Ray Telescope (XRT) observations for three nonmagnetic nova-like (NL) cataclysmic variables (CVs; MV Lyr, BZ Cam, V592 Cas) in order to study characteristics of boundary layers (BLs) in CVs. The nonmagnetic NLs are found mostly in a state of high mass accretion rate ( 1 × 10 −9 M yr −1 ), and some show occasional low states. Using the XRT data, we find optically thin multipletemperature cooling flow type emission spectra with X-ray temperatures (kT max ) of 21-50 keV. These hard X-rayemitting BLs diverge from simple isobaric cooling flows, indicating X-ray temperatures that are of virial values in the disk. In addition, we detect power-law emission components from MV Lyr and BZ Cam and plausibly from V592 Cas, which may be a result of the Compton scattering of the optically thin emission from the fast wind outflows in these systems and/or Compton upscattering of the soft disk photons. The X-ray luminosities of the (multitemperature) thermal plasma emission in the 0.1-50.0 keV range are (0.9-5.0) × 10 32 erg s −1 . The ratio of the X-ray and disk luminosities (calculated from the UV-optical wavelengths) yields an efficiency (L x /L disk ) ∼ 0.01-0.001. Given this non-radiative ratio for the X-ray-emitting BLs with no significant optically thick blackbody emission in the soft X-rays (consistent with ROSAT observations), together with the high/virial X-ray temperatures, we suggest that high-state NL systems may have optically thin BLs merged with ADAF-like flows and/or X-ray coronae. In addition, we note that the axisymmetric bipolar and/or rotation-dominated fast-wind outflows detected in these three NLs (particularly BZ Cam and V592 Cas) or some other NL may also be explained in the context of ADAF-like BL regions.

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X-ray spectral variations of U Gem from quiescence to outburst

Cited by 12 publications

References 27 publications

X-Ray Emissions from Accreting White Dwarfs: A Review

X-Ray Emissions from Accreting White Dwarfs: A Review

The Fall and the Rise of X-Rays from Dwarf Novae in Outburst:RXTEObservations of VW Hydri and WW Ceti

SWIFTX-RAY TELESCOPE OBSERVATIONS OF THE NOVA-LIKE CATACLYSMIC VARIABLES MV Lyr, BZ Cam, AND V592 Cas

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